Lateralization of brain function
The median longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum.
Function lateralization, such as semantics, intonation, accentuation, and prosody, has since been called into question and largely been found to have a neuronal basis in both hemispheres.
Language functions such as grammar, vocabulary and literal meaning are typically lateralized to the left hemisphere, especially in right-handed individuals.
Because of this functional division of the left and right sides of the body and of the space that surrounds it, the processing of information in the sensory cortices is essentially identical.
That is, the processing of visual and auditory stimuli, spatial manipulation, facial perception, and artistic ability are represented bilaterally.
[13][14] Rather than just being a series of places where different brain modules occur, there are running similarities in the kind of function seen in each side, for instance how right-side impairment of drawing ability making patients draw the parts of the subject matter with wholly incoherent relationships, or where the kind of left-side damage seen in language impairment not damaging the patient's ability to catch the significance of intonation in speech.
People with left hemisphere damage may have impaired perception of high resolution, or detailed, aspects of an image.
People with right hemisphere damage may have impaired perception of low resolution, or big picture, aspects of an image.
While the ability to speak fluently with normal melodic intonation is spared, the language produced by a person with Wernicke's aphasia is riddled with semantic errors and may sound nonsensical to the listener.
The concept of "right-brained" or "left-brained" individuals is considered a widespread myth which oversimplifies the true nature of the brain's cerebral hemispheres (for a recent counter position, though, see below).
[26] For example, the implications of the research have no bearing on psychological interventions such as eye movement desensitization and reprocessing (EMDR) and neurolinguistic programming,[27][28] brain-training equipment, or management training.
[32][33] In the 19th century and to a lesser extent the 20th, it was thought that each side of the brain was associated with a specific gender: the left corresponding with masculinity and the right with femininity and each half could function independently.
[35] One of the first indications of brain function lateralization resulted from the research of French physician Pierre Paul Broca, in 1861.
[36] German physician Karl Wernicke continued in the vein of Broca's research by studying language deficits unlike expressive aphasia.
These seminal works on hemispheric specialization were done on patients or postmortem brains, raising questions about the potential impact of pathology on the research findings.
In the 1940s, neurosurgeon Wilder Penfield and his neurologist colleague Herbert Jasper developed a technique of brain mapping to help reduce side effects caused by surgery to treat epilepsy.
They found that stimulation of one hemisphere's motor cortex produces muscle contraction on the opposite side of the body.
Research by Michael Gazzaniga and Roger Wolcott Sperry in the 1960s on split-brain patients led to an even greater understanding of functional laterality.
This led to many interesting behavioral phenomena that allowed Gazzaniga and Sperry to study the contributions of each hemisphere to various cognitive and perceptual processes.
