The Last Supper

original digitized image

original digitized image

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How Leonardo da Vinci

pictured the Last Supper

article link

The Last Supper (1494-1498) by Leonardo da Vinci
in the refectory of Santa Maria delle Grazie in Milan

During the bitter-cold first week in February, I went to snow-bound Milan to write stories about an annual world-class food-and-wine event called “IdentitàGolose” and Milan University’s Library and Archive of Egyptology. With great good luck (because the obligatory reservations made online via www.milan-museum.com often have a two-month backlog), I was able to squeeze in a same-day visit, which lasts barely 15 minutes, to see Leonardo da Vinci’s masterpiece, The Last Supper, one of his 17 paintings and the only one not on canvas. I’d seen it only once before, almost 50 years ago. Just a month before Easter, I thought I’d share with ITV readers the unique way polymath Leonardo (1452-1519), a sculptor, architect, musician, draftsman, scientist, mathematician, engineer, anatomist, geologist, and cartographer, as well as painter, pictured this prelude to Our Savior’s sacrifice by telling this spellbinding mural’s story.

A self-portrait of Da Vinci depicted as the Apostle Jude Thaddeus

THE PAINTING

In 1482, Leonardo da Vinci, then 30, left Tuscany to be the court painter for Duke Ludovico Sforza (1451-1508) and his wife Duchess Beatrice d’Este (1475-1497) in Milan. A decade or so later, his patron commissioned Leonardo to paint The Last Supper as the centerpiece of his planned mausoleum in the monastery of the recently-completed Dominican Church of Santa Maria delle Grazie, which was later remodeled by Bramante, also the architect of St. Peter’s Basilica. Leonardo began work, which was supposed to take a year, in 1494, but did not complete the painting until 1498. According to Wikipedia’s article about Leonardo, “the novelist Matteo Bandello observed Leonardo at work and wrote that some days he would paint from dawn to dusk without stopping to eat and then not paint for three or four days at a time. This was beyond the comprehension of the prior of the convent, who hounded him until Leonardo

asked Ludovico to intervene. Vasari describes how Leonardo, troubled over his ability to depict the faces of Christ and Judas (Iscariot), told the Duke that he might be obliged to use the prior as his ‘model’ for Judas.”

It is generally believed that the white-bearded Apostle on the right of the painting, Jude Thaddeus, is the artist’s self-portrait.

Leonardo also probably cryptically “signed” this work; the knot at the end of the tablecloth’s right-hand edge represents the Latin word for knot, vincium.

An earlier version of the scene: The Last Supper by Ghirlandaio (1482). Located in Florence

LEONARDO’S CONCEPTION

The Last Supper theme was a traditional one for refectories, although this room wasn’t a refectory at the time Leonardo painted his masterpiece on the north wall. His work of art represents the Last Supper as told in the Gospel of John 13:21, when Jesus announces that one of his twelve Apostles would betray him before sunrise, but does not reveal which one. We know that Leonardo studied earlier paintings by Ghirlandaio and Andrea del Castagno with traditional iconography that focuses instead on the moment of the traitor’s identification, when Judas, who is represented in an isolated position with respect to the other Apostles, receives a piece of bread from Jesus and dips it in his dish. Leonardo, however, preferred the moment prior to this, dominated by doubt. His is the first version of this theme with the Apostles displaying the human emotions of doubt, shock, fear, and anger through the expressions on their faces, the movements of their hands, and their body language, which contrast with Jesus’ calmness. It should also be mentioned that the daylight and unbroken bread confirm that it is too early for Judas to have been identified as the traitor.

Giacomo Raffaelli’s life-size mosaic copy of Leonardo’s
Last Supper (1809-14), now in Vienna’s Minoritenkirche

TECHNIQUE

A wall panel in the entrance to the refectory explains: “Leonardo creates a sense of continuity between the actual space of the refectory and the painted space through an exceptional use of perspective, which has Christ’s right temple as its vanishing point; all the lines of perspective in the composition guide the viewer’s eye towards Jesus’ face, the narrative center of the work.” Leonardo’s early ideas, both notes and preparatory drawings, for this painting are illustrated in a sheet of figure studies, no. 12542r, conserved in the Royal Library at Windsor Castle.

Another first is that Leonardo’s Judas is not seated as is customary with his back to the viewer and, unlike the other well-lit Apostles, is in a shadow. He is also holding a purse. Although he would not yet have received the 30 silver coins, he was the treasurer for the Apostles. Until The Notebooks of Leonardo da Vinci were discovered during the 19th century, only Judas, Peter, John and Jesus could be positively identified.

The painting contains several references to the number 3 or the Blessed Trinity. The Apostles are seated in groups of three: to the left of Jesus (from the viewer’s point of view): Bartholomew, James the Lesser, and Andrew; Peter, Judas Iscariot, and John; to the right of Jesus: Thomas, James the Greater, and Philip; Matthew, Jude Thaddeus, and Simon the Zealot; there are three windows behind Jesus; and the shape of Jesus’ figure resembles a triangle.

MEDIUM

Also unique to The Last Supper is the medium Leonardo, always the inventor, used. According to Wikipedia, “he painted it on a dry wall rather than on wet plaster, so it is not a true fresco. Since a fresco cannot be modified as the artist works, Leonardo instead chose to seal the stone wall with a layer of pitch, gesso, and mastic, then paint onto the sealing layer with tempera.” Because of the method he used so that he, a known procrastinator with a marked tendency to leave projects unfinished, could make changes, his masterpiece began to deteriorate after a few years. The only evidence we have of what the original painting looked like is a 16th-century oil canvas by an unknown artist, in approximately original size, now housed in the Premonstratensian monastery, founded in 1128, at Tongerlo in Westerlo near Antwerp in Belgium. The copy reveals many details that are no longer visible in the original fresco, in particular the food, the room’s décor, and the landscape. Between 1809 and 1814 the Roman mosaic artist Giacomo Raffaelli made another life-size copy, commissioned by Napoleon and now in the Viennese Minoritenkirche.

The Last Supper by Dalí

DETERIORATION

In 1517, Don Antonio de Beatis was the first to testify that Leonardo’s painting “is already beginning to be damaged.” Some 50 years later, in 1566, Leonardo’s biographer Giorgio Vasari wrote in his Lives: “Of the original by Leonardo (…) one can now perceive only a glaring stain.” A century later, the Dominican Fathers enlarged the door at the center of the wall that connected the refectory to the kitchen, which, although later bricked up, is still visible. It eliminated the part that depicted Christ’s feet, which, through early copies, were supposedly in a position symbolizing his forthcoming crucifixion. Further damage was done in 1768 when a curtain was hung over the painting to protect it; instead it trapped moisture on the surface, and whenever pulled back, scratched the flaking paint. In 1722, an English traveler testified that the rough wall was visible in various parts of the “fresco.” In 1799, when Napoleon’s troops turned the refectory into a stable and barn, the painting suffered still further vandalism. The soldiers passed their free time throwing stones at the painting and climbed ladders to scratch out the Apostles’ eyes. In 1812, the monastery of Santa Maria delle Grazie was used as a headquarters by the fire brigade and subsequently as a military barracks. In 1934, the refectory became a state museum, while the church and the cloisters were returned to the Dominicans. During the Second World War, on the night of August 15, 1943, a bomb struck the cloisters, causing the collapse of the refectory’s vault and its east wall. The Last Supper was saved from bomb splinters thanks to sandbags put in place at the start of the war. After a long period of “open air,” the collapsed parts of the refectory were rebuilt in 1947.

The Last Supper by Andy Warhol

RESTORATION

The Last Supper by Andy Warhol

A first restoration was attempted in 1726 by Michelangelo Bellotti, who filled in missing sections with oil paint and then varnished the whole mural; many others followed over the next two centuries. By the end of the 1970s the painting’s appearance had so badly deteriorated that, from 1978 to 1999, Pinin Brambilla Barcilon guided a major restoration project, which, in a sealed, climate-controlled ambience, undertook to stabilize the painting permanently and reverse the damage caused by dirt, pollution and the misguided 18th- and 19th- century restoration attempts. On May 28th, 1999, the painting was put back on display.

In 1980, UNESCO made the Santa Maria delle Grazie complex and The Last Supper a World Heritage site.

SPECULATIONS

Perhaps because of its deteriorated state, Leonardo’s Last Supper has been the target of much speculation by historians and writers, usually centered around purported hidden messages within the painting.

Several examples follow:

1) The Templar Revelation (1997) by Lynn Pickett and Clive Prince and The Da Vinci Code (2003) by Dan Brown both identify the person seated at Jesus’s right hand not as John the Apostle, but as a woman, and none other than Mary Magdalene, who supposedly bore Christ’s child after his death. It is true that the beardless John looks quite effeminate, but he was much younger than the other Apostles except for Phillip and maybe Matthew, both of whom are beardless here, too, while the others all have beards. Moreover, the Bible never mentions Mary Magdalene as present at the Last Supper, and if John is Mary, then where is John?

2) According to an article by Matthew Moore published on July 30, 2007 in The Telegraph, Slavisa Pesci, “an information technologist and amateur scholar,” superimposed Leonardo’s version of The Last Supper on its mirror image (with both images of Jesus lined up) and claimed that the resultant picture has a Templar Knight on the far left, a woman dressed in orange and holding a swaddled baby in her arms to the left of Jesus, and the Holy Grail in the form of a chalice in front of Jesus. With the naked eye no chalice is visible, although Jesus’ left hand is pointing to the Eucharist and his right to a glass of wine.

3) Giovanni Maria Pala, an Italian musician, has indicated that the positions of the hands and loaves of bread can be interpreted as notes on a musical staff, and, if read from right to left (because Leonardo was left-handed), form a musical composition.

4) Reported by British Vatican correspondent Richard Owen in an article entitled, “Da Vinci ‘predicted the world would end in 4066’ says Vatican researcher” in the London Times on March 15, 2010, is the most far-fetched of all theories. Sabrina Sforza Galitzia claimed to have deciphered the “mathematical and astrological” puzzle in Leonardo’s The Last Supper. She said that Leonardo foresaw the end of the world in a “universal flood” which would begin on March 21, 4006, and end on November 1 the same year. Leonardo believed that this would mark “a new start for humanity.”

The Last Supper by Escobar

Leonardo’s Last Supper is open all day Tuesday to Sunday from 8:15 AM to 7 PM with a maximum group of 25 people admitted every 15 minutes. Closed Mondays and on January 1st, May 1st, and Christmas Day. My same-day ticket, reserved by my hotel, cost 8 euros.

Epilogue

If you can’t make it to Milan, in Room VIII of the Pinocateca in the Vatican Museums there’s a Flemish tapestry of the Last Supper designed by Raphael, and in Raphael’s loggia on the second floor of the Apostolic Palace, one of the frescoes executed by Raphael’s workshop from 1517-19 is of the Last Supper. One of the frescoes on the northern wall of the Sistine Chapel, devoted to scenes from the life of Jesus and painted by Cosimo Rosselli (1431-1507) in 1481-2, also depicts the Last Supper.

There are several modern renditions of the Last Supper in the US. In 1955, Salvador Dalí painted The Sacrament of the Last Supper, one of the most popular paintings in the National Gallery of Art in Washington, DC. Sculptor Marisol Escobar was inspired by Leonardo’s Last Supper. Her work is in New York’s Metropolitan Museum of Art. And in 1986, Andy Warhol was commissioned to produce a series of paintings based on The Last Supper. They were first exhibited in a bank across the street from Santa Maria delle Grazie. This was Warhol’s last series of paintings before his death. On loan from the Andy Warhol Museum in his hometown of Pittsburgh, one of Warhol’s many paintings of The Last Supper (the Museum, at 117 Sandusky Street, owns three others) will take part in the traveling exhibition of 300 works “Andy Warhol: 15 Minutes Eternal” to commemorate the 25th anniversary of the artist’s death. The exhibition opened at the ArtScience Museum, Marina Bay Sands, in Singapore on March 17 and will travel to five other Asian cities: Hong Kong, Shanghai, Beijing, and Tokyo, over the next 27 months.

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POEMS

The Last Supper, by Lydia Sigourney

The Last Supper, by Jack Stewart

The Last Supper, by Rainer Maria Rilke

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10 Secrets of The Last Supper

by Leonardo da Vinci

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The Last Supper by Leonardo da Vinci

In 1495, Leonardo da Vinci began what would become one of history's most influential works of art - The Last Supper

The Last Supper is Leonardo's visual interpretation of an event chronicled in all four of the Gospels (books in the Christian New Testament). The evening before Christ was betrayed by one of his disciples, he gathered them together to eat, tell them he knew what was coming and wash their feet (a gesture symbolizing that all were equal under the eyes of the Lord). As they ate and drank together, Christ gave the disciples explicit instructions on how to eat and drink in the future, in remembrance of him. It was the first celebration of the Eucharist, a ritual still performed.

Specifically, The Last Supper depicts the next few seconds in this story after Christ dropped the bombshell that one disciple would betray him before sunrise, and all twelve have reacted to the news with different degrees of horror, anger, and shock.

Leonardo hadn't worked on such a large painting and had no experience in the standard mural medium of fresco. The painting was made using experimental pigments directly on the dry plaster wall and unlike frescos, where the pigments are mixed with the wet plaster, it has not stood the test of time well. Even before it was finished there were problems with the paint flaking from the wall and Leonardo had to repair it. Over the years it has crumbled, been vandalized bombed and restored. Today we are probably looking at very little of the original.

Much of the recent interest in the painting has centered on the details hidden within the painting, but in directing attention to these 'hidden' details, most people miss the incredible sense of perspective the work displays. The sharp angling of the walls within the picture, which leads back to the seemingly distant back wall of the room and the windows that show the hills and sky beyond. The type of day shown through these windows adds to the feeling of serenity that rests in the center of the piece, around the figure of Christ.

The Layout of The Last Supper

The Last Supper Perspective

Leonardo balanced the perspective construction of the Last Supper so that its vanishing point is immediately behind Christ's right temple, pointing to the physical location of the center, or sensus communis, of his brain. By pulling a string in radial directions from this point, he marked the table ends, floor lines, and orthogonal edges of the six ceiling coffer columns. From the right and/or left edge of the horizon line, he drew diagonal lines up to the coffer corners, locating points for the horizontal lines of the 12 coffer rows.

Leonardo was well known for his love of symmetry. In his Last Supper, the layout is largely horizontal. The large table is seen in the foreground of the image with all of the figures behind it. The painting is largely symmetrical with the same number of figures on either side of Jesus. The above diagram shows how the perspective the Last Super was worked out with a series of marks at key points highlighting the architectural aspects of the composition and positioning of the figures.

10 Facts You Might not

Know about the Masterpiece

1. Who's who in "The Last Supper"

Who's who in the Last Supper

2. The secret of "The Last Supper"

The Last Supper is a very popular religious scene painted by many celebrated artists. Unlike artists before and after him, Leonardo da Vinci chose not to put halos on Jusus Christ. Many art historians believe that Leonardo da Vinci believe in nature, not in God. To Leonardo, nature is God, so he treated every character in the fresco as common people.

3. "Last Supper" is a failed experiment.

Unlike traditional frescoes, which Renaissance masters painted on wet plaster walls, Leonardo experimented with tempura paint on a dry, sealed plaster wall in the Santa Maria delle Grazie monastery in Milan, Italy. The experiment proved unsuccessful, however, because the paint did not adhere properly and began to flake away only a few decades after the work was finished.

4. The spilled salt is symbolic.

Speculations about symbolism in the artwork are plentiful. For example, many scholars have discussed the meaning of the spilled salt container near Judas's elbow. Spilled salt could symbolize bad luck, loss, religion, or Jesus as salt of the earth.

5. Eel or herring?

Scholars have also remarked on da Vinci's choice of food. They dispute whether the fish on the table is herring or eel since each carries its own symbolic meaning. In Italian, the word for eel is "aringa." The similar word, "arringa," means to indoctrinate. In northern Italian dialect, the word for herring is "renga," which also describes someone who denies religion. This would fit with Jesus' biblical prediction that his apostle Peter would deny knowing him.

6. Da Vinci used a hammer and nail to help him to achieve the one-point perspective.

What makes the masterpiece so striking is the perspective from which it's painted, which seems to invite the viewer to step right into the dramatic scene. To achieve this illusion, da Vinci hammered a nail into the wall, then tied string to it to make marks that helped guide his hand in creating the painting's angles.

7. The existing mural is not 100% da Vinci's work.

At the end of the 20th century, restorer Panin Brambilla Barcilon and his crew relied on microscopic photographs, core samples, infrared reflectoscopy and sonar to remove the added layers of paint and restore the original as accurately as possible. Critics maintain that only a fraction of the painting that exists today is the work of Leonardo da Vinci.

8. Three early copies of the original exist.

Three of da Vinci's students, including Giampietrino, made copies of his painting early in the 16th century. Giampietrino did a full-scale copy that is now in London's Royal Academy of Arts. This oil painting on canvas was the primary resource for the latest restoration of the work. The second copy by Andrea Solari is in the Leonardo da Vinci Museum in Belgium while the third copy by Cesare da Sesto is in the Church of Saint Ambrogio in Switzerland.

The Last Supper Copy - by Giampietrino

9. The painting is also a musical score.

According to Italian musician Giovanni Maria Pala, da Vinci incorporated musical notes in "The Last Supper." In 2007, Pala created a 40-second melody from the notes that were allegedly hidden in the scene.

10. The painting has been a victim of neglect and abuse.

In 1652, monastery residents cut a new door in the wall of the deteriorating painting, which removed a chunk of the artwork showing the feet of Jesus. Late in the 18th century, Napoleon Bonaparte's soldiers turned the area into a stable and further damaged the wall with projectiles. During World War II, the Nazis bombed the monastery, reducing surrounding walls to rubble.

Part 3 - CHATBOT and I discuss "Neuroscience and Consciousness"

Part 3 - CHATBOT and I discuss

"Neuroscience and Consciousness"

by ChatGPT 3.5 & R.E. Slater

July 29, 2024

PLEASE GIVE ME AN EXAMPLE SHOWING THE RELATIONSHIP BETWEEN NEUROSCIENCE AND THE SCIENCE OF CONSCIOUSNESS

ChatGPT

Certainly! Here's a text-based flow diagram that illustrates the relationship between neuroscience and the science of consciousness:

Flow Diagram: Relationship between Neuroscience and the Science of Consciousness

1. Neuroscience

   • Focus: Study of the nervous system, including the brain, spinal cord, and networks of neurons.
   • Key Areas:
     • Neuroanatomy: Structure of the nervous system.
     • Neurophysiology: Function of the nervous system.
     • Neurochemistry: Chemical processes in the nervous system.
     • Neuroplasticity: Ability of the brain to reorganize itself.

2. Science of Consciousness

• Focus: Understanding the nature, origins, and mechanisms of conscious experience.
• Key Areas:
• Phenomenology: Study of subjective experiences.
• Philosophy of Mind: Theoretical understanding of consciousness.
• Cognitive Science: Interdisciplinary study involving psychology, neuroscience, and artificial intelligence.
• Quantum Consciousness: Hypothetical connection between quantum mechanics and consciousness.

1. Intersection of Neuroscience and Consciousness

   • Neural Correlates of Consciousness (NCCs):
     • Identifying brain regions and networks associated with conscious experience.
     • Example: The role of the prefrontal cortex and parietal lobes in conscious awareness.
   • Mechanisms of Awareness:
     • How neural activity translates to conscious experience.
     • Example: Theories like Integrated Information Theory (IIT) and Global Workspace Theory (GWT).

2. Key Relationships and Interactions

   • Brain Activity and Conscious States:
     • Relationship between neural activity (e.g., EEG patterns) and states of consciousness (e.g., wakefulness, sleep, altered states).
   • Disorders of Consciousness:
     • Insights from conditions like coma, vegetative states, and locked-in syndrome.
     • Understanding how specific brain injuries affect consciousness.
   • Neuroimaging Techniques:
     • Use of fMRI, PET scans, and EEG to study brain activity related to conscious experiences.
   • Cognitive Functions:
     • Connection between higher cognitive functions (e.g., memory, attention) and conscious awareness.

3. Research and Implications

   • Clinical Applications:
     • Understanding consciousness can improve treatments for mental health conditions and brain injuries.
   • Artificial Intelligence:
     • Insights into consciousness can inform the development of AI and machine learning systems that mimic human cognition.
   • Philosophical Implications:
     • Ongoing debates about the nature of consciousness, the mind-body problem, and the possibility of non-human consciousness.

Diagram Summary

• Neuroscience focuses on the biological basis of brain function.
• Science of Consciousness seeks to understand the nature of conscious experience.
• The intersection involves identifying neural correlates, studying mechanisms of awareness, and exploring the implications for understanding the mind and brain.

By understanding these relationships, researchers aim to uncover how subjective experiences arise from physical processes in the brain, potentially bridging the gap between the physical and experiential worlds.

Feel free to ask if you'd like more detailed information on any specific point!

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Neural correlates of consciousness

From Wikipedia, the free encyclopedia

The neuronal correlates of consciousness (NCC) constitute the smallest set of neural events and structures sufficient for a given conscious percept or explicit memory. This case involves synchronized action potentials in neocortical pyramidal neurons.^[1]

The neural correlates of consciousness (NCC) are the minimal set of neuronal events and mechanisms sufficient for the occurrence of the mental states to which they are related.^[2] Neuroscientists use empirical approaches to discover neural correlates of subjective phenomena; that is, neural changes which necessarily and regularly correlate with a specific experience.^[3][4] The set should be minimal because, under the materialist assumption that the brain is sufficient to give rise to any given conscious experience, the question is which of its components are necessary to produce it.

Neurobiological approach to consciousness

A science of consciousness must explain the exact relationship between subjective mental states and brain states, the nature of the relationship between the conscious mind and the electrochemical interactions in the body (mind–body problem). Progress in neuropsychology and neurophilosophy has come from focusing on the body rather than the mind. In this context the neuronal correlates of consciousness may be viewed as its causes, and consciousness may be thought of as a state-dependent property of an undefined complex, adaptive, and highly interconnected biological system.^[5]

Discovering and characterizing neural correlates does not offer a causal theory of consciousness that can explain how particular systems experience anything, the so-called hard problem of consciousness,^[6] but understanding the NCC may be a step toward a causal theory. Most neurobiologists propose that the variables giving rise to consciousness are to be found at the neuronal level, governed by classical physics. There are theories proposed of quantum consciousness based on quantum mechanics.^[7]

There is an apparent redundancy and parallelism in neural networks so, while activity in one group of neurons may correlate with a percept in one case, a different population may mediate a related percept if the former population is lost or inactivated. It may be that every phenomenal, subjective state has a neural correlate. Where the NCC can be induced artificially, the subject will experience the associated percept, while perturbing or inactivating the region of correlation for a specific percept will affect the percept or cause it to disappear, giving a cause-effect relationship from the neural region to the nature of the percept.

Proposals that have been advanced over the years include: what characterizes the NCC? What are the commonalities between the NCC for seeing and for hearing? Will the NCC involve all the pyramidal neurons in the cortex at any given point in time? Or only a subset of long-range projection cells in the frontal lobes that project to the sensory cortices in the back? Neurons that fire in a rhythmic manner? Neurons that fire in a synchronous manner?^[8]

The growing ability of neuroscientists to manipulate neurons using methods from molecular biology in combination with optical tools (e.g., Adamantidis et al. 2007) depends on the simultaneous development of appropriate behavioral assays and model organisms amenable to large-scale genomic analysis and manipulation. It is the combination of fine-grained neuronal analysis in animals with increasingly more sensitive psychophysical and brain imaging techniques in humans, complemented by the development of a robust theoretical predictive framework, that will hopefully lead to a rational understanding of consciousness, one of the central mysteries of life.

Level of arousal and content of consciousness

There are two common but distinct dimensions of the term consciousness,^[9] one involving arousal and states of consciousness and the other involving content of consciousness and conscious states. To be conscious of anything the brain must be in a relatively high state of arousal (sometimes called vigilance), whether in wakefulness or REM sleep, vividly experienced in dreams although usually not remembered. Brain arousal level fluctuates in a circadian rhythm but may be influenced by lack of sleep, drugs and alcohol, physical exertion, etc. Arousal can be measured behaviorally by the signal amplitude that triggers some criterion reaction (for instance, the sound level necessary to evoke an eye movement or a head turn toward the sound source). Clinicians use scoring systems such as the Glasgow Coma Scale to assess the level of arousal in patients.

High arousal states are associated with conscious states that have specific content, seeing, hearing, remembering, planning or fantasizing about something. Different levels or states of consciousness are associated with different kinds of conscious experiences. The "awake" state is quite different from the "dreaming" state (for instance, the latter has little or no self-reflection) and from the state of deep sleep. In all three cases the basic physiology of the brain is affected, as it also is in altered states of consciousness, for instance after taking drugs or during meditation when conscious perception and insight may be enhanced compared to the normal waking state.

Clinicians talk about impaired states of consciousness as in "the comatose state", "the persistent vegetative state" (PVS), and "the minimally conscious state" (MCS). Here, "state" refers to different "amounts" of external/physical consciousness, from a total absence in coma, persistent vegetative state and general anesthesia, to a fluctuating and limited form of conscious sensation in a minimally conscious state such as sleep walking or during a complex partial epileptic seizure.^[10] The repertoire of conscious states or experiences accessible to a patient in a minimally conscious state is comparatively limited. In brain death there is no arousal, but it is unknown whether the subjectivity of experience has been interrupted, rather than its observable link with the organism. Functional neuroimaging have shown that parts of the cortex are still active in vegetative patients that are presumed to be unconscious;^[11] however, these areas appear to be functionally disconnected from associative cortical areas whose activity is needed for awareness.

The potential richness of conscious experience appears to increase from deep sleep to drowsiness to full wakefulness, as might be quantified using notions from complexity theory that incorporate both the dimensionality as well as the granularity of conscious experience to give an integrated-information-theoretical account of consciousness.^[12] As behavioral arousal increases so does the range and complexity of possible behavior. Yet in REM sleep there is a characteristic atonia, low motor arousal and the person is difficult to wake up, but there is still high metabolic and electric brain activity and vivid perception.

Many nuclei with distinct chemical signatures in the thalamus, midbrain and pons must function for a subject to be in a sufficient state of brain arousal to experience anything at all. These nuclei therefore belong to the enabling factors for consciousness. Conversely, it is likely that the specific content of any particular conscious sensation is mediated by particular neurons in the cortex and their associated satellite structures, including the amygdala, thalamus, claustrum and the basal ganglia.

Neuronal basis of perception

The possibility of precisely manipulating visual percepts in time and space has made vision a preferred modality in the quest for the NCC. Psychologists have perfected a number of techniques – masking, binocular rivalry, continuous flash suppression, motion induced blindness, change blindness, inattentional blindness – in which the seemingly simple and unambiguous relationship between a physical stimulus in the world and its associated percept in the privacy of the subject's mind is disrupted.^[13] In particular a stimulus can be perceptually suppressed for seconds or even minutes at a time: the image is projected into one of the observer's eyes but is invisible, not seen. In this manner the neural mechanisms that respond to the subjective percept rather than the physical stimulus can be isolated, permitting visual consciousness to be tracked in the brain. In a perceptual illusion, the physical stimulus remains fixed while the percept fluctuates. The best known example is the Necker cube whose 12 lines can be perceived in one of two different ways in depth.

The Necker Cube: The left line drawing can be perceived in one of two distinct depth configurations shown on the right. Without any other cue, the visual system flips back and forth between these two interpretations.^[14]

A perceptual illusion that can be precisely controlled is binocular rivalry. Here, a small image, e.g., a horizontal grating, is presented to the left eye, and another image, e.g., a vertical grating, is shown to the corresponding location in the right eye. In spite of the constant visual stimulus, observers consciously see the horizontal grating alternate every few seconds with the vertical one. The brain does not allow for the simultaneous perception of both images.

Logothetis and colleagues^[15] recorded a variety of visual cortical areas in awake macaque monkeys performing a binocular rivalry task. Macaque monkeys can be trained to report whether they see the left or the right image. The distribution of the switching times and the way in which changing the contrast in one eye affects these leaves little doubt that monkeys and humans experience the same basic phenomenon. In the primary visual cortex (V1) only a small fraction of cells weakly modulated their response as a function of the percept of the monkey while most cells responded to one or the other retinal stimulus with little regard to what the animal perceived at the time. But in a high-level cortical area such as the inferior temporal cortex along the ventral stream almost all neurons responded only to the perceptually dominant stimulus, so that a "face" cell only fired when the animal indicated that it saw the face and not the pattern presented to the other eye. This implies that NCC involve neurons active in the inferior temporal cortex: it is likely that specific reciprocal actions of neurons in the inferior temporal and parts of the prefrontal cortex are necessary.

A number of fMRI experiments that have exploited binocular rivalry and related illusions to identify the hemodynamic activity underlying visual consciousness in humans demonstrate quite conclusively that activity in the upper stages of the ventral pathway (e.g., the fusiform face area and the parahippocampal place area) as well as in early regions, including V1 and the lateral geniculate nucleus (LGN), follow the percept and not the retinal stimulus.^[16] Further, a number of fMRI^[17][18] and DTI experiments^[19] suggest V1 is necessary but not sufficient for visual consciousness.^[20]

In a related perceptual phenomenon, flash suppression, the percept associated with an image projected into one eye is suppressed by flashing another image into the other eye while the original image remains. Its methodological advantage over binocular rivalry is that the timing of the perceptual transition is determined by an external trigger rather than by an internal event. The majority of cells in the inferior temporal cortex and the superior temporal sulcus of monkeys trained to report their percept during flash suppression follow the animal's percept: when the cell's preferred stimulus is perceived, the cell responds. If the picture is still present on the retina but is perceptually suppressed, the cell falls silent, even though primary visual cortex neurons fire.^[21][22] Single-neuron recordings in the medial temporal lobe of epilepsy patients during flash suppression likewise demonstrate abolishment of response when the preferred stimulus is present but perceptually masked.^[23]

Global disorders of consciousness

Given the absence of any accepted criterion of the minimal neuronal correlates necessary for consciousness, the distinction between a persistently vegetative patient who shows regular sleep-wave transitions and may be able to move or smile, and a minimally conscious patient who can communicate (on occasion) in a meaningful manner (for instance, by differential eye movements) and who shows some signs of consciousness, is often difficult. In global anesthesia the patient should not experience psychological trauma but the level of arousal should be compatible with clinical exigencies.

Midline structures in the brainstem and thalamus necessary to regulate the level of brain arousal. Small, bilateral lesions in many of these nuclei cause a global loss of consciousness.^[24]

Blood-oxygen-level-dependent fMRI have demonstrated normal patterns of brain activity in a patient in a vegetative state following a severe traumatic brain injury when asked to imagine playing tennis or visiting rooms in his/her house.^[25] Differential brain imaging of patients with such global disturbances of consciousness (including akinetic mutism) reveal that dysfunction in a widespread cortical network including medial and lateral prefrontal and parietal associative areas is associated with a global loss of awareness.^[26] Impaired consciousness in epileptic seizures of the temporal lobe was likewise accompanied by a decrease in cerebral blood flow in frontal and parietal association cortex and an increase in midline structures such as the mediodorsal thalamus.^[27]

Relatively local bilateral injuries to midline (paramedian) subcortical structures can also cause a complete loss of awareness.^[28] These structures therefore enable and control brain arousal (as determined by metabolic or electrical activity) and are necessary neural correlates. One such example is the heterogeneous collection of more than two dozen nuclei on each side of the upper brainstem (pons, midbrain and in the posterior hypothalamus), collectively referred to as the reticular activating system (RAS). Their axons project widely throughout the brain. These nuclei – three-dimensional collections of neurons with their own cyto-architecture and neurochemical identity – release distinct neuromodulators such as acetylcholine, noradrenaline/norepinephrine, serotonin, histamine and orexin/hypocretin to control the excitability of the thalamus and forebrain, mediating alternation between wakefulness and sleep as well as general level of behavioral and brain arousal. After such trauma, however, eventually the excitability of the thalamus and forebrain can recover and consciousness can return.^[29] Another enabling factor for consciousness are the five or more intralaminar nuclei (ILN) of the thalamus. These receive input from many brainstem nuclei and project strongly, directly to the basal ganglia and, in a more distributed manner, into layer I of much of the neocortex. Comparatively small (1 cm³ or less) bilateral lesions in the thalamic ILN completely knock out all awareness.^[30]

Forward versus feedback projections

Many actions in response to sensory inputs are rapid, transient, stereotyped, and unconscious.^[31] They could be thought of as cortical reflexes and are characterized by rapid and somewhat stereotyped responses that can take the form of rather complex automated behavior as seen, e.g., in complex partial epileptic seizures. These automated responses, sometimes called zombie behaviors,^[32] could be contrasted by a slower, all-purpose conscious mode that deals more slowly with broader, less stereotyped aspects of the sensory inputs (or a reflection of these, as in imagery) and takes time to decide on appropriate thoughts and responses. Without such a consciousness mode, a vast number of different zombie modes would be required to react to unusual events.

A feature that distinguishes humans from most animals is that we are not born with an extensive repertoire of behavioral programs that would enable us to survive on our own ("physiological prematurity"). To compensate for this, we have an unmatched ability to learn, i.e., to consciously acquire such programs by imitation or exploration. Once consciously acquired and sufficiently exercised, these programs can become automated to the extent that their execution happens beyond the realms of our awareness. Take, as an example, the incredible fine motor skills exerted in playing a Beethoven piano sonata or the sensorimotor coordination required to ride a motorcycle along a curvy mountain road. Such complex behaviors are possible only because a sufficient number of the subprograms involved can be executed with minimal or even suspended conscious control. In fact, the conscious system may actually interfere somewhat with these automated programs.^[33]

From an evolutionary standpoint it clearly makes sense to have both automated behavioral programs that can be executed rapidly in a stereotyped and automated manner, and a slightly slower system that allows time for thinking and planning more complex behavior. This latter aspect may be one of the principal functions of consciousness. Other philosophers, however, have suggested that consciousness would not be necessary for any functional advantage in evolutionary processes.^[34][35] No one has given a causal explanation, they argue, of why it would not be possible for a functionally equivalent non-conscious organism (i.e., a philosophical zombie) to achieve the very same survival advantages as a conscious organism. If evolutionary processes are blind to the difference between function F being performed by conscious organism O and non-conscious organism O*, it is unclear what adaptive advantage consciousness could provide.^[36] As a result, an exaptive explanation of consciousness has gained favor with some theorists that posit consciousness did not evolve as an adaptation but was an exaptation arising as a consequence of other developments such as increases in brain size or cortical rearrangement.^[37] Consciousness in this sense has been compared to the blind spot in the retina where it is not an adaption of the retina, but instead just a by-product of the way the retinal axons were wired.^[38] Several scholars including Pinker, Chomsky, Edelman, and Luria have indicated the importance of the emergence of human language as an important regulative mechanism of learning and memory in the context of the development of higher-order consciousness.

It seems possible that visual zombie modes in the cortex mainly use the dorsal stream in the parietal region.^[31] However, parietal activity can affect consciousness by producing attentional effects on the ventral stream, at least under some circumstances. The conscious mode for vision depends largely on the early visual areas (beyond V1) and especially on the ventral stream.

Seemingly complex visual processing (such as detecting animals in natural, cluttered scenes) can be accomplished by the human cortex within 130–150 ms,^[39][40] far too brief for eye movements and conscious perception to occur. Furthermore, reflexes such as the oculovestibular reflex take place at even more rapid time-scales. It is quite plausible that such behaviors are mediated by a purely feed-forward moving wave of spiking activity that passes from the retina through V1, into V4, IT and prefrontal cortex, until it affects motorneurons in the spinal cord that control the finger press (as in a typical laboratory experiment). The hypothesis that the basic processing of information is feedforward is supported most directly by the short times (approx. 100 ms) required for a selective response to appear in IT cells.

Conversely, conscious perception is believed to require more sustained, reverberatory neural activity, most likely via global feedback from frontal regions of neocortex back to sensory cortical areas^[20] that builds up over time until it exceeds a critical threshold. At this point, the sustained neural activity rapidly propagates to parietal, prefrontal and anterior cingulate cortical regions, thalamus, claustrum and related structures that support short-term memory, multi-modality integration, planning, speech, and other processes intimately related to consciousness. Competition prevents more than one or a very small number of percepts to be simultaneously and actively represented. This is the core hypothesis of the global workspace theory of consciousness.^[41][42]

In brief, while rapid but transient neural activity in the thalamo-cortical system can mediate complex behavior without conscious sensation, it is surmised that consciousness requires sustained but well-organized neural activity dependent on long-range cortico-cortical feedback.

History

The neurobiologist Christfried Jakob (1866–1956) argued that the only conditions which must have neural correlates are direct sensations and reactions; these are called "intonations".^{[citation needed]}

Neurophysiological studies in animals provided some insights on the neural correlates of conscious behavior. Vernon Mountcastle, in the early 1960s, set up to study this set of problems, which he termed "the Mind/Brain problem", by studying the neural basis of perception in the somatic sensory system. His labs at Johns Hopkins were among the first, along with Edward V.Evarts at NIH, to record neural activity from behaving monkeys. Struck with the elegance of SS Stevens approach of magnitude estimation, Mountcastle's group discovered three different modalities of somatic sensation shared one cognitive attribute: in all cases the firing rate of peripheral neurons was linearly related to the strength of the percept elicited. More recently, Ken H. Britten, William T. Newsome, and C. Daniel Salzman have shown that in area MT of monkeys, neurons respond with variability that suggests they are the basis of decision making about direction of motion. They first showed that neuronal rates are predictive of decisions using signal detection theory, and then that stimulation of these neurons could predictably bias the decision. Such studies were followed by Ranulfo Romo in the somatic sensory system, to confirm, using a different percept and brain area, that a small number of neurons in one brain area underlie perceptual decisions.

Other lab groups have followed Mountcastle's seminal work relating cognitive variables to neuronal activity with more complex cognitive tasks. Although monkeys cannot talk about their perceptions, behavioral tasks have been created in which animals made nonverbal reports, for example by producing hand movements. Many of these studies employ perceptual illusions as a way to dissociate sensations (i.e., the sensory information that the brain receives) from perceptions (i.e., how the consciousness interprets them). Neuronal patterns that represent perceptions rather than merely sensory input are interpreted as reflecting the neuronal correlate of consciousness.

Using such design, Nikos Logothetis and colleagues discovered perception-reflecting neurons in the temporal lobe. They created an experimental situation in which conflicting images were presented to different eyes (i.e., binocular rivalry). Under such conditions, human subjects report bistable percepts: they perceive alternatively one or the other image. Logothetis and colleagues trained the monkeys to report with their arm movements which image they perceived. Temporal lobe neurons in Logothetis experiments often reflected what the monkeys' perceived. Neurons with such properties were less frequently observed in the primary visual cortex that corresponds to relatively early stages of visual processing. Another set of experiments using binocular rivalry in humans showed that certain layers of the cortex can be excluded as candidates of the neural correlate of consciousness. Logothetis and colleagues switched the images between eyes during the percept of one of the images. Surprisingly the percept stayed stable. This means that the conscious percept stayed stable and at the same time the primary input to layer 4, which is the input layer, in the visual cortex changed. Therefore, layer 4 can not be a part of the neural correlate of consciousness. Mikhail Lebedev and their colleagues observed a similar phenomenon in monkey prefrontal cortex. In their experiments monkeys reported the perceived direction of visual stimulus movement (which could be an illusion) by making eye movements. Some prefrontal cortex neurons represented actual and some represented perceived displacements of the stimulus. Observation of perception related neurons in prefrontal cortex is consistent with the theory of Christof Koch and Francis Crick who postulated that neural correlate of consciousness resides in prefrontal cortex. Proponents of distributed neuronal processing may likely dispute the view that consciousness has a precise localization in the brain.

Francis Crick wrote a popular book, "The Astonishing Hypothesis", whose thesis is that the neural correlate for consciousness lies in our nerve cells and their associated molecules. Crick and his collaborator Christof Koch^[43] have sought to avoid philosophical debates that are associated with the study of consciousness, by emphasizing the search for "correlation" and not "causation".^{[needs update]}

There is much room for disagreement about the nature of this correlate (e.g., does it require synchronous spikes of neurons in different regions of the brain? Is the co-activation of frontal or parietal areas necessary?). The philosopher David Chalmers maintains that a neural correlate of consciousness, unlike other correlates such as for memory, will fail to offer a satisfactory explanation of the phenomenon; he calls this the hard problem of consciousness.^[44][45]

See also

• Animal consciousness
• Artificial consciousness
• Binding problem
• Bridge locus
• Cognitive map
• Conceptual space
• Global workspace theory
• Hard problem of consciousness
• Higher-order theories of consciousness
• Image schema
• Information-theoretic death
• Integrated information theory
• LIDA (cognitive architecture)
• Models of neural computation
• Multiple drafts model
• Münchhausen trilemma
• Neural coding
• Neural decoding
• Neural substrate
• Philosophy of mind
• Quantum cognition
• Quantum mind

Notes

1. ^ Koch 2004, Figure 1.1 The Neuronal Correlates of Consciousness p. 16.
2. ^ Koch 2004, p. 304.
3. ^ See here Archived 2013-03-13 at the Wayback Machine for a glossary of related terms.
4. ^ Chalmers, David J. (June 1998), "What is a neural correlate of consciousness?", in Metzinger, Thomas (ed.), Neural Correlates of Consciousness:Empirical and Conceptual Questions, MIT Press (published September 2000), ISBN 978-0-262-13370-8
5. ^ Squire 2008, p. 1223.
6. ^ Kandel 2007, p. 382.
7. ^ Schwartz, Jeffrey M.; Stapp, Henry P.; Beauregard, Mario. "Quantum physics in neuroscience and psychology: A neurophysiological model of mind/brain interaction" (PDF).
8. ^ See Chalmers 1998, available online.
9. ^ Zeman 2001
10. ^ Schiff 2004
11. ^ Laureys, Trends Cogn Sci, 2005, 9:556–559
12. ^ Tononi et al. 2016
13. ^ Kim and Blake 2004
14. ^ Koch 2004, Figure 16.1 The Bistable Necker Cube, p. 270.
15. ^ Logothetis 1998
16. ^ Rees and Frith 2007
17. ^ Haynes and Rees 2005
18. ^ Lee et al. 2007
19. ^ Shimono and Niki 2013
20. ^ Jump up to:^a b Crick and Koch 1995
21. ^ Leopold and Logothetis 1996
22. ^ Sheinberg and Logothetis 1997
23. ^ Kreiman et al. 2002
24. ^ Koch 2004, Figure 5.1 The Cholinergic Enabling System p. 92. See Chapter 5, available on line.
25. ^ Owen et al. 2006
26. ^ Laureys 2005
27. ^ Blumenfeld et al. 2004
28. ^ Koch 2004, p. 92
29. ^ Villablanca 2004
30. ^ Bogen 1995
31. ^ Jump up to:^a b Milner and Goodale 1995
32. ^ Koch and Crick 2001
33. ^ Beilock et al. 2002
34. ^ Flanagan, Owen; Polger, Tom W. (1995). "Zombies and the function of consciousness". Journal of Consciousness Studies. 2: 313–321.
35. ^ Rosenthal, David (2008). "Consciousness and its function". Neuropsychologia. 46 (3): 829–840. doi:10.1016/j.neuropsychologia.2007.11.012. PMID 18164042. S2CID 7791431.
36. ^ Harnad, Stevan (2002). "Turing indistinguishability and the Blind Watchmaker". In Fetzer, James H. (ed.). Consciousness Evolving. John Benjamins. Retrieved 2011-10-26.
37. ^ Feinberg, T.E.; Mallatt, J. (2013). "The evolutionary and genetic origins of consciousness in the Cambrian Period over 500 million years ago". Front Psychol. 4: 667. doi:10.3389/fpsyg.2013.00667. PMC 3790330. PMID 24109460.
38. ^ Robinson, Zack; Maley, Corey J.; Piccinini, Gualtiero (2015). "Is Consciousness a Spandrel?". Journal of the American Philosophical Association. 1 (2): 365–383. doi:10.1017/apa.2014.10. S2CID 170892645.
39. ^ Thorpe et al. 1996
40. ^ VanRullen and Koch 2003
41. ^ Baars 1988
42. ^ Dehaene et al. 2003
43. ^ Koch, Christof (2004). The quest for consciousness: a neurobiological approach. Englewood, US-CO: Roberts & Company Publishers. ISBN 978-0-9747077-0-9.
44. ^ See Cooney's foreword to the reprint of Chalmers' paper: Brian Cooney, ed. (1999). "Chapter 27: Facing up to the problem of consciousness". The place of mind. Cengage Learning. pp. 382 ff. ISBN 978-0534528256.
45. ^ Chalmers, David (1995). "Facing up to the problem of consciousness". Journal of Consciousness Studies. 2 (3): 200–219. Archived from the original on 2005-03-08. Retrieved 2019-01-18. See also this link

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Further reading

• Atkinson, A., et al. "Consciousness: Mapping the theoretical landscape"
• Chalmers, D (1995). The Conscious Mind: In Search of a Fundamental Theory. Philosophy of Mind. Oxford: Oxford University Press. ISBN 9780195117899.
• Crick, Francis (1994). The astonishing hypothesis: the scientific search for the soul. Macmillan Reference USA. ISBN 978-0-684-19431-8.
• Dawkins, MS (1993). Through our eyes only? The Search for Animal Consciousness. Oxford: Oxford University Press. ISBN 9780198503200.
• Edelman, GM; Tononi, G (2000). Consciousness: How Matter becomes Imagination. New York: Basic Books. ISBN 9780465013777.
• Goodale, MA; Milner, AD (2004). Sight Unseen: An Exploration of Conscious and Unconscious Vision. Oxford: Oxford University Press. ISBN 978-0-19-856807-0.
• Koch C. and Hepp K. (2006) Quantum mechanics and higher brain functions: Lessons from quantum computation and neurobiology. Nature 440: 611–2. (Freely available from http://www.theswartzfoundation.org/papers/caltech/koch-hepp-07-final.pdf (2007))
• Logothetis, N. K.; Guggenberger, Heinz; Peled, Sharon; Pauls, Jon (1999). "Functional imaging of the monkey brain". Nature Neuroscience. 2 (6): 555–562. doi:10.1038/9210. PMID 10448221. S2CID 21627829.
• Schall, J. "On Building a Bridge Between Brain and Behavior." Annual Reviews in Psychology. Vol 55. Feb 2004. pp 23–50.
• Vaas, Ruediger (1999): "Why Neural Correlates Of Consciousness Are Fine, But Not Enough". Anthropology & Philosophy Vol. 3, pp. 121–141. https://web.archive.org/web/20120205025719/http://www.swif.uniba.it/lei/mind/texts/t0000009.htm

External links

Wikibooks has a book on the topic of: Consciousness studies

• Newsome Lab Publications.