The corpus
callosum is a large, C-shaped nerve fiber bundle found beneath the cerebral cortex.It stretches across the midline of the brain, connecting the left and
right cerebral hemispheres. It makes up the largest collection of white matter tissue found in the brain.
To understand the role of the corpus callosum, it is first important to remember that the brain is divided into two cerebral hemispheres (right and left). The hemispheres are made distinct from one another by a long groove called the medial longitudinal fissure. On a large scale, the two hemispheres are nearly identical, but on a microscopic and functional level there are some differences.
When
information like sensory data is sent to the brain it is typically received
first in one hemisphere. For example, when you type on your keyboard,
information about the feel of the keys is sent up from your right hand to the primary somatosensory cortex on the left side of your brain. That
information, however, must then be shared with the right side of your brain as
well. That’s where the corpus callosum comes into play. It is a large bundle of
fibers that connects the left and right hemispheres, and it carries information
received in one hemisphere over to the other.
In the second half of the twentieth
century, Roger Sperry, Michael Gazzaniga, and others studied patients whose
corpus callosum had been severed in a procedure called a corpus callosotomy. The procedure is normally undertaken as a last-resort treatment of epilepsy, as it can stop seizures from spreading from one hemisphere of the
brain to another. The patients became known as split-brain patients.
Surprisingly, a corpus callosotomy can
be completed without severe side effects; the side effects that do appear are
often language related. Sperry and Gazzaniga explored language deficits in
callosotomy patients in detail. In the process, they learned some interesting
things about how language centers are distributed across the cerebral
hemispheres and how the corpus callosum facilitates communication between the
two sides of the brain.
Sperry and Gazzaniga presented
split-brain patients with visual stimuli, but only to one eye at a time. For
example, they would present an image of a flower to the right eye, but cover
the left eye. They found that split-brain patients, when presented with a
visual image to only their left eye, could not name the object shown in the
image.
Sperry and colleagues hypothesized that
this occurred because visual information for the majority of the visual field
travels to the opposite side of the brain to be processed. If the object is
shown to the left eye, most of the information travels to the right side of the
brain. Normally, this information would then be shared with the opposite
hemisphere by way of the corpus callosum. The researchers suggested that
split-brain individuals could not name the object if it was shown only to the
left eye because the visual information was not reaching the left side of the
brain, which is where our important language centers are located.
Much of what you’ve heard about one
cerebral hemisphere being dominant in the management of a particular skill or
capacity is probably exaggerated. For example, someone who is creative doesn’t
likely have an overall bias toward thinking with the right side of her brain.
Instead, most skills are spread fairly evenly throughout both hemispheres.
Language, however, appears to be an exception. In most people, speech is
generated in the left hemisphere, and thus the left hemisphere is considered to
be the dominant hemisphere for language.
Thus, according to Sperry and Gazzaniga,
because language centers are located in the left side of the brain, when an
image is presented to the left eye of a split-brain patient, the patient’s
language areas are not privy to the visual information. The information travels
to the right hemisphere but does not cross back over to the left due to the
severed corpus callosum. So, the ability to place a name to the object is
limited.
These experiments helped to demonstrate
the importance of the left hemisphere in language processing as well as the
importance of the corpus callosum in bridging the two cerebral hemispheres.
However, they also demonstrated the versatility and resiliency of the brain, as
in most split-brain patients other tracts like the anterior commissure still carry enough information between the cerebral hemispheres to
allow overall functionality to be somewhat normal.
Source: https://neuroscientificallychallenged.com/posts/know-your-brain-corpus-callosum
Images via SlideShare
Source: Corpus Callosum – Scents of Science (myfusimotors.com)
No comments:
Post a Comment