The human brain's hemispheres, while appearing similar, possess specialized functions (cortical lateralization), with the left typically handling language and logic, and the right managing spatial and holistic processing, though both hemispheres work together for most tasks.
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although the left and right side to the
human cortex look almost identical the
hemispheres have specialized functions
you might have heard that the left brain
is analytical and logical while the
right is more intuitive and creative the
idea that people are either left-brained
or right-brained is very popular but it
turns out thankfully that we use our
whole brain we just recruit to the left
and right hemispheres for different
tasks a phenomenon known as cortical
lateralization let's explore this in
this woman is facing us so her left is
on our right and vice versa the primary
motor cortex which controls voluntary
movement is located roughly here
we know from work of German physiologist
Edward insig in the 1860s that this part
of the brain has a contralateral
connection to the body parts it controls
which means that it is connected to the
opposite side hit seek first noticed
this while caring for wounded soldiers
he found that touching the surface of a
specific strip of cortex caused movement
on the opposite side of the body the
various primary sensory areas also have
this contralateral organization such
that incoming sensory information from
the body is sent to the cortex on the
opposite side the primary somatosensory
cortex is located just behind the motor
strip which is responsible for the
perception of touch sensations it
receives its information from sensory
neurons whose axons cross over so that
the right side of the body talked to the
left somatosensory strip and the left
side of the body tops to the right the
connections of these primary sensory
motor areas of the cortex are also
symmetrical and that the left and right
sides of the body have equal
representation in their respective hemispheres
let's consider the organization of
information from the visual system to
the cortex
unlike the somatosensory system which
sends signals separately from each side
of the body the visual system is a
little different because the left and
right eyes capture images from both the
left and right side to visual space as
shown in this figure
for example the outside part of the
right eye and the inside part of the
left eye detect stimuli in the left
visual field shown in red the pathway
from the inside part of the left eye
crosses over at the optic chiasm and the
signals then get sent to the right
hemisphere the pathway from the outside
part of the right eye stays on the same
side so ultimately the signals from the
left visual world all end up in the
right hemisphere if you follow the green
lines you can see that this is the same
arrangement for the right visual field
as well in other words information from
left and right visual space is sent to
the primary visual cortex from the
opposite side in a way that conserves
unlike the primary sensory motor areas
the association cortex is asymmetrical
because it's functions differ between
the left and right hemispheres the left
hemisphere appears to have a stronger
role in processing language and logical
based thought while the right is
involved in more holistic spatial type
tasks most people about 95% of
right-handers and 85% of left-handers
show this bias although a small
proportion of people have the opposite arrangement
