FoundationalConceptsNeuroscience

Does each hemisphere experience a separate awareness of “what it is
like to be?”
The neural conditions sufficient for manifestation of conscious
awareness (subjective experience) are often referred to as neural
correlates of consciousness (NCC). Such correlates have not been char-
acterized. Thus, it is not straightforward to ask and obtain an answer
to a question of the form: does the nonspeaking right hemisphere of a
split-brain patient exhibit consciousness awareness? Or, more gener-
ally, is a patient in a coma or vegetative state consciously aware? What
about when asleep, or while sedated by general anesthesia?
Among speculations on the nature of the NCC, manifestations of
connectivity are generally held as prime contenders. One proposal for
a neural correlate of consciousness has been high-frequency (gamma-
range) synchronous electrical oscillation over widespread regions
of the cerebral cortex, linking or binding together neural activity in
many different cortical regions. Another hypothesis for NCC is that
electrodynamic interconnection in the brain must be of a kind of com-
plexity that maximizes the way information interacts—a kind of max-
imally “integrated” information.
The human cerebral cortex—if it were to be unfolded, smoothing
out all the gyri and sulci—is approximately 2.5 square feet, or 2,300
square centimeters, about the size of a circular pizza 21 inches in
diameter. The average thickness of the gray matter of our cerebral cor-
tex is around 3 millimeters. Multiplying this by the cortical area yields
a volume of 690,000 cubic millimeters. The approximate number of
neurons and glial cells in the human cerebral cortex is currently esti-
mated to be twenty billion and forty billion, respectively. This means
that each cubic millimeter of cerebral cortex in the human brain has
approximately thirty thousand neurons and sixty thousand glial cells
(Fig. 18.5). This densely packed region of neurons and glia, together