Hemispheric Differences

connections called commissures. In the early 1940’s, American surgeonWilliam

van Wagenen, in order to stop the spread of epileptic seizures from

crossing from one hemisphere to the other, performed the first procedure

of cutting the 200 million fibers of the corpus callosum. The results were

mixed, however, and it was not until the 1960’s that two other American surgeons,

Joe Bogen and P. J. Vogel, decided to try the operation again, this

time also including some cutting of commissure fibers. The results reduced

or stopped the seizures in most patients. However, extensive testing by

American psychobiologist Roger Sperry and his colleagues demonstrated

unique behavioral changes in the patients, called split-brain syndrome. Research

with split-brain syndrome and less invasive imaging techniques of the

brain, such as computed tomography (CT) and positron-emission tomography

(PET) scans, has demonstrated many anatomical and functional differences

between the left and right hemispheres.

The degree of differences between the two cerebral hemispheres varies

greatly, depending on a number of factors. Males develop the greatest

lateralization•differences between the hemispheres•and develop the differences

soonest. Those with a dominant right hand have greater lateralization

than left- or mixed-handers. Therefore, when there is talk of “left

brain versus right brain,” it is important to keep in mind that a greater degree

of difference exists in right-handed males. A minority of people, usu

ally left-handers, show little differences between the left and right hemispheres.

ally left-handers, show little differences between the left and right hemispheres.

The right hemisphere (RH) tends to be larger and heavier than the left

hemisphere (LH), with the greatest difference in the frontal lobe. Conversely,

several other neurological areas have been found to be larger in the

LH: the occipital lobe, the planum temporale, Wernicke’s area, and the

Sylvian fissure. An interesting gender difference in hemispheric operation

is that the LH amygdala is more active in females, whereas the RH amygdala

is more active in males.

The left-brain/right-brain functional dichotomy has been the subject of

much popular literature. While there are many differences in operation between

the two hemispheres, many of these differences are subtle, and in

many regards both hemispheres are involved in the psychological function

in question, only to different degrees.

The most striking difference between the two hemispheres is that the RH

is responsible for sensory and motor functions of the left side of the body,

and the LH controls those same functions for the body’s right side. This

contralateral control is found, to a lesser degree, for hearing and, due to the

optic chiasm, not at all for vision.

In the domain of sound and communication, the LH plays a greater role

in speech production, language comprehension, phonetic and semantic

analysis, visual word recognition, grammar, verbal learning, lyric recitation,

musical performance, and rhythm keeping. A greater RH contribution is

found in interpreting nonlanguage sounds, reading Braille, using emotional

tone in language, understanding humor and sarcasm, expressing and

interpreting nonverbal communication (facial and bodily expressions), and

perceiving music. Categorical decisions, the understanding of metaphors,

and the figurative aspects of language involve both hemispheres.

Regarding other domains, the RH plays a greater role in mathematical

operations, but the LH is essential for remembering numerical facts and the

reading and writing of numbers. Visually, the RH contributes more to mental

rotation, facial perception, figured/ground distinctions, map reading,

and pattern perception. Detail perception draws more on LH resources.

The RH is linked more with negative emotions such as fear, anger, pain, and

sadness, while positive affect is associated more with the LH. Exceptions are

that schizophrenia, anxiety, and panic attacks have been found to be related

more to increases in LH activity.

ally left-handers, show little differences between the left and right hemispheres.

The right hemisphere (RH) tends to be larger and heavier than the left

hemisphere (LH), with the greatest difference in the frontal lobe. Conversely,

several other neurological areas have been found to be larger in the

LH: the occipital lobe, the planum temporale, Wernicke’s area, and the

Sylvian fissure. An interesting gender difference in hemispheric operation

is that the LH amygdala is more active in females, whereas the RH amygdala

is more active in males.

The left-brain/right-brain functional dichotomy has been the subject of

much popular literature. While there are many differences in operation between

the two hemispheres, many of these differences are subtle, and in

many regards both hemispheres are involved in the psychological function

in question, only to different degrees.

The most striking difference between the two hemispheres is that the RH

is responsible for sensory and motor functions of the left side of the body,

and the LH controls those same functions for the body’s right side. This

contralateral control is found, to a lesser degree, for hearing and, due to the

optic chiasm, not at all for vision.

In the domain of sound and communication, the LH plays a greater role

in speech production, language comprehension, phonetic and semantic

analysis, visual word recognition, grammar, verbal learning, lyric recitation,

musical performance, and rhythm keeping. A greater RH contribution is

found in interpreting nonlanguage sounds, reading Braille, using emotional

tone in language, understanding humor and sarcasm, expressing and

interpreting nonverbal communication (facial and bodily expressions), and

perceiving music. Categorical decisions, the understanding of metaphors,

and the figurative aspects of language involve both hemispheres.

Regarding other domains, the RH plays a greater role in mathematical

operations, but the LH is essential for remembering numerical facts and the

reading and writing of numbers. Visually, the RH contributes more to mental

rotation, facial perception, figured/ground distinctions, map reading,

and pattern perception. Detail perception draws more on LH resources.

The RH is linked more with negative emotions such as fear, anger, pain, and

sadness, while positive affect is associated more with the LH. Exceptions are

that schizophrenia, anxiety, and panic attacks have been found to be related

more to increases in LH activity.

The right hemisphere (RH) tends to be larger and heavier than the left

hemisphere (LH), with the greatest difference in the frontal lobe. Conversely,

several other neurological areas have been found to be larger in the

LH: the occipital lobe, the planum temporale, Wernicke’s area, and the

Sylvian fissure. An interesting gender difference in hemispheric operation

is that the LH amygdala is more active in females, whereas the RH amygdala

is more active in males.

The left-brain/right-brain functional dichotomy has been the subject of

much popular literature. While there are many differences in operation between

the two hemispheres, many of these differences are subtle, and in

many regards both hemispheres are involved in the psychological function

in question, only to different degrees.

The most striking difference between the two hemispheres is that the RH

is responsible for sensory and motor functions of the left side of the body,

and the LH controls those same functions for the body’s right side. This

contralateral control is found, to a lesser degree, for hearing and, due to the

optic chiasm, not at all for vision.

In the domain of sound and communication, the LH plays a greater role

in speech production, language comprehension, phonetic and semantic

analysis, visual word recognition, grammar, verbal learning, lyric recitation,

musical performance, and rhythm keeping. A greater RH contribution is

found in interpreting nonlanguage sounds, reading Braille, using emotional

tone in language, understanding humor and sarcasm, expressing and

interpreting nonverbal communication (facial and bodily expressions), and

perceiving music. Categorical decisions, the understanding of metaphors,

and the figurative aspects of language involve both hemispheres.

Regarding other domains, the RH plays a greater role in mathematical

operations, but the LH is essential for remembering numerical facts and the

reading and writing of numbers. Visually, the RH contributes more to mental

rotation, facial perception, figured/ground distinctions, map reading,

and pattern perception. Detail perception draws more on LH resources.

The RH is linked more with negative emotions such as fear, anger, pain, and

sadness, while positive affect is associated more with the LH. Exceptions are

that schizophrenia, anxiety, and panic attacks have been found to be related

more to increases in LH activity.