Brain’s Conscious Experiences Unveiled

More than a quarter of all stroke sufferers have an unusual disease in which they lose cognitive awareness of half of what their eyes see.
Following a stroke in the right half of the brain, for example, a person may consume only what is on the right side of the plate because their conscious experiences are absent for the other half. The individual may only see the right half of a photograph and disregard a person on their left side.

Surprisingly, such stroke victims can have emotional reactions to the full snapshot or setting. Their brains appear to be taking it all in, but these folks have conscious of half of the environment.

This perplexing condition, known as unilateral neglect, brings to light a long-standing topic in brain science: What is the distinction between perceiving something and being aware or cognizant that you are perceiving it? You may not have noticed a shoe store while browsing through your Instagram feed, but you began looking for shoe discounts online. Things that you don’t consciously notice are recorded by your brain.

Neuroscientists from the Hebrew University of Jerusalem and the University of California, Berkeley, claim to have discovered the region of the brain where these sustained visual pictures are stored for the few seconds we view them. They published their findings in the journal Cell Reports this month.

“Conscious experience, and in particular, visual experience, is the most fundamental thing that everyone feels from the moment they open their eyes when they wake up in the morning to the moment they go to sleep,” said Hebrew University graduate student Gal Vishne, lead author of the paper. “Our study is about your everyday experience.”

While the findings do not yet explain how we can be unaware of what we perceive, studies like these could have practical applications in the future, perhaps allowing doctors to tell whether a coma patient is still aware of the outside world and potentially able to improve based on brain activity. Understanding conscious experience may also aid doctors in developing remedies for consciousness problems.

“The inspiration for my whole scientific career comes from patients with stroke who suffer from unilateral neglect, where they just ignore half of the world,” said senior author Leon Deouell, a Hebrew University professor of psychology and member of the Edmond and Lily Safra Center for brain research. “That actually triggered my whole interest in the question of conscious awareness. How is it that you can have the information, but still not acknowledge it as something that you’re subjectively experiencing, not act upon it, not move your eyes to it, not grab it? What is required for something not only to be sensed by the brain, but for you to have a subjective experience? Understanding that would eventually help us understand what is missing in the cognitive system and in the brains of patients who have this kind of a syndrome.”

“We are adding a piece to the puzzle of conscious experiences —how things remain in your mind’s eye for you to act on,” added Robert Knight, also a senior author and a UC Berkeley professor of psychology and member of the Helen Wills Neuroscience Institute.

The brain has two types of responses: transitory and persistent

Deouell observed that for the past six decades, electrical investigations of the human brain have nearly entirely focused on the initial burst of activity following perception. However, this increase fades after around 300 or 400 milliseconds, but humans frequently look at and are mindful of things for seconds or longer.

“That leaves a whole lot of time which is not explained in neural terms,” he said.

In order to track cerebral activity linked with epileptic seizures, the neuroscientists received permission to conduct studies on ten persons whose skulls were opened so that electrodes could be put on the brain surface. The electrodes were used to measure brain activity while the researchers showed different images to the patients on a computer screen for varying durations of time, up to 1.5 seconds. To ensure that the patients were paying attention, they were required to touch a button whenever they saw an article of clothing.

Most technologies for recording neural activity in people, such as functional MRI (fMRI) or electroencephalography (EEG), allow researchers to make detailed judgments about where and when brain activity occurs, but not both. The Hebrew University/UC Berkeley team were able to bridge this gap by implanting electrodes into the skull.

The team discovered that, contrary to previous studies that found only a brief burst of activity in the brain when something new was perceived, the visual areas of the brain actually retained information about the percept at a low level of activity for much longer. The sustained pattern of brain activity was comparable to the original pattern and altered when a person looked at a new image.
“This stable representation suggests a neural basis for stable perception over time, despite the changing level of activity,” Deouell said.

Unlike previous research, they discovered that the prefrontal and parietal cortexes at the front of the brain only become active when anything new is perceived, with information fading completely after half a second (500 milliseconds), even for a considerably longer stimulus.

The occipitotemporal portion of the visual cortex in the back of the brain likewise becomes very active for a brief period of time—around 300 milliseconds—before dropping to a sustained but low level, roughly 10% to 20% of the original spike. However, the pattern of activity does not disappear; it continues unmodified for about as long as a person watches an image.

“The frontal cortex is involved in the detection of something new,” Deouell explained. “But you also see an ongoing representation in the higher-level sensory regions.”

The brain’s sequence of events could be interpreted in a variety of ways. According to Knight and Vishne, conscious awareness occurs when the prefrontal cortex accesses continuous activity in the visual cortex. Deouell believes that awareness develops via connections between several parts of the brain, including the prefrontal cortex.

A group calling itself the Cogitate Consortium has corroborated the team’s results. Though the consortium’s findings are still being peer reviewed, they were described during a June event in New York City framed as a debate between two “leading” theories of consciousness. Both the Cell Reports findings and the unpublished findings could be explained by either theory of awareness.

“That adversarial collaboration involves two theories out of something like 22 current theories of consciousness,” Deouell cautioned. “Many theories usually means that we don’t understand.”

Nonetheless, the two research, as well as other current studies as part of the Templeton Foundation’s adversarial collaboration, could lead to a true, testable theory of consciousness.

“Regarding the predictions of the two theories which we were able to test, both are correct. But looking at the broader picture, none of the theories in their current form work, even though we find each to have some grain of truth, at the moment,” Vishne said. “With so much still unknown about the neural basis of consciousness, we believe that more data should be collected before a new phoenix can rise out of the ashes of the previous theories. ”

Future research by Deouell and Knight will look at the electrical activity connected with consciousness in other areas of the brain, such as those dealing with memory and emotions.

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