FoundationalConceptsNeuroscience

cortex make connections to neurons in V1, damage to V1 produces a
substantial disruption to the flow of visual information in the brain.
Corresponding to whatever region of the spatial map in V1 that has
been impacted by the lesion, there will be blindness to the corre-
sponding region of visual space.
If the lesion is small, the scotoma may not even be noticeable to the
patient, unless careful testing is conducted. If the lesion is sufficiently
large, then the patient will experience an absence of information from
part of visual space. A large lesion might completely damage all of V1
in one hemisphere of the cortex, resulting in complete loss of vision
for an entire half of the visual field, the half of visual space contralat-
eral to the side of the brain in which the lesion is located. The clinical
term to describe this is hemianopsia, meaning loss of vision in one half
of visual space.
A lesion in V4 produces a disruption of color vision. Depending
upon the extent of the lesion, larger or smaller regions of visual space
may be affected. The color disruption may vary from washed out or
faded color perception to a complete loss of color awareness. This is a
cortical achromatopsia, because the cause is related to a cortical lesion
rather than to a retinal condition as in retinal achromatopsia. A lesion
in V5 produces an akinetopsia, or motion blindness, in which the per-
son is unaware of movement in some region or regions of visual space.
It is as if the world appears as a series of snapshots—a very disabling
condition, especially if one needs to navigate around in places where
there are moving vehicles.
There is a region in the inferior (lower) and medial (middle) tempo-
ral lobe that has been found, in both monkeys and humans, to contain
cells that respond selectively to images of faces. Sustaining a lesion
in this area may bring on a clinical condition called prosopagnosia
(Greek prosopon = face), in which the person has great difficulty or