The Frontal Cortex

Comatose?

In the latest New Yorker, the always fascinating and fair Jerome Groopman* has an article on the recent Science paper documenting neural activity in vegetative patients:

For four months, Kate Bainbridge had not spoken or responded to her family or her doctors, although her eyes were often open and roving. (A person in a coma appears to be asleep and is unaware of even painful stimulation; a person in a vegetative state has periods of wakefulness but shows no awareness of her environment and does not make purposeful movements.) Owen placed Bainbridge in a PET scanner, a machine that records changes in metabolism and blood flow in the brain, and, on a screen in front of her, projected photographs of faces belonging to members of her family, as well as digitally distorted images, in which the faces were unrecognizable. Whenever pictures of Bainbridge’s family flashed on the screen, an area of her brain called the fusiform gyrus, which neuroscientists had identified as playing a central role in face recognition, lit up on the scan. “We were stunned,” Owen told me. “The fusiform-gyrus activation in her brain was not simply similar to normal; it was exactly the same as normal volunteers’.”

I think the best way to understand these vegetative patients is through the prism of blindsight. (I discuss blindsight in the Virginia Woolf chapter of my forthcoming book.) Before Lawrence Weiskrantz began his investigations in the early 1970′s, scientists had assumed that lesions in the primary visual areas (the V1) caused irreparable blindness. They were wrong.

Lesions in the V1 only cause conscious blindness, a phenomenon Weiskrantz named “blindsight”. Although these patients think they are blind, they can actually see, at least unconsciously. What they are missing is awareness. While their eyes continue to transmit visual information, and undamaged parts of their brain continue to process this information, blindsight patients are unable to consciously access what their brain knows.

So how can you tell blindsight and blindness apart? Blindsight patients exhibit an astonishing talent. On various visual tasks they perform with an aptitude impossible for the totally blind. For example, they can “guess” with uncanny accuracy whether they were shown a square or a circle, or whether a light has been flashed. While they have no explicit awareness of the light, they can still respond to it, albeit without knowing what they are responding to it. Brain scans confirm their absurd claims, as the areas associated with self-awareness show little or no activity, while the areas associated with vision show relatively normal activity.

This is what makes blindsight patients so poignantly fascinating: their consciousness has been divorced from their sensation. Although their brain continues to “see,” their mind can’t pay attention to these visual inputs. They are unable to subjectively interpret the information entering their cortex. As Virginia Woolf wondered in The Waves: “How to describe the world seen without a self?” “There are no words,” she answered, and she was right. These comatose patients demonstrate that even if our brain is processing sensations, something else is required before those sensations can be sensed. All of our perceptions need a perceiver.

*Did you read his last article on colic? They should dispense that article in sex-ed class. Nothing makes for effective birth control like the prospect of having a baby screaming non-stop for six months.

Comments

  1. #1 Chris
    October 9, 2007

    Really interesting stuff; I’m anxious to read your upcoming book.
    At the Beyond Belief symposium a couple last year, V.S. Ramachandran had a really wondering account of some blindsight patients that he worked with. Here’s the link: http://beyondbelief2006.org/watch/

    I cant remember if it was in session 4 or in session 10, but I recall watching his talk a handful of times because it was so fascinating.