Lateralization of brain function

As a lateralization of the brain is called the neuroanatomical and functional diversity of tasks and specialization of the cerebral hemispheres. The brain of most higher organisms is constructed morphologically bilaterally. Although this symmetry is indicative of a much similar construction, we know for a long time from a variety of observations and experiments, that the roles and functions of the brain have undergone a spatial specialization. Some functions or sub-functions of the brain are preferably carried out in one of the two halves of the brain. The distribution of processes on the right and left halves is called lateralization.

The cerebrum consists of two strongly furrowed hemispheres ( hemispheres ) by a deep cut - separated - the brain longitudinal furrow ( longitudinal fissure ). The connection between the two hemispheres is produced by a thick nerve cord, the so-called beam ( corpus callosum ).

Anatomical asymmetries

As anatomical asymmetries of the hemispheres macroscopically or microscopically detectable differences of corresponding structures of the two halves of the brain are called. Macroscopic differences in the volumes of circumscribed brain areas as well as to the length, depth and shape of brain furrows can be determined. Microscopic examination shows that among themselves there are differences in the incidence of individual cell types and their networking.

The most important asymmetries affect the sylvian sulcus, the planum temporale, the Heschl gyrus, the central sulcus and the occipital and frontal width. Means that even in 70% of cases demonstrate that the Sylvian sulcus is more extensive in the left hemisphere. This is especially true for right-handers. In addition, shows up for the left hemisphere a greater specific weight, a greater insular cortex, a greater proportion of gray matter, a larger inferior temporal lobe and nucleus lateralis posterior of the thalamus. Eventually, the left frontal lobe is narrower.

Functional asymmetries

Methods

Early studies on the functional specialization of the hemispheres are based in large part on neurological and neuropsychological studies on the effects of brain injury ( lesions) on cognitive abilities. By comparing two patients with lesions in different hemispheres of the double dissociation can be concluded that the functional lateralization on the basis of the principle.

Since the 1960s, the connection between the hemispheres was surgically removed in split-brain patients, which enabled an experimental study of the workings of the brain hemispheres. Hemispheres can also be reversibly blocked using the Wada test.

Due to the ethical problems through human testing surgical interventions were frequently the result of a simultaneous, partially successful, treatment of epileptics. Due to technical progress imaging techniques such as magnetic resonance imaging have received an increasing importance over the last decades.

Lateralization of cognitive abilities

The best-known example of the functional asymmetry of the dominance of the left hemisphere in language production, which can be detected in approximately 95% of right-handers and 70% of left-handers. Studies of split-brain patients have shown that a processed only in the right hemisphere stimulus does not allow linguistic- expressive utterances. Furthermore, the left brain is considered in the word recognition and mathematical operations as dominant. A dominance of the right hemisphere can be detected among other things the spatial perception and face recognition.

Right - Shift Theory

After the developed Annett Right shift theory language dominance of the left hemisphere was due to a single gene. This influence would not only be associated with an inhibition of the corresponding development in the right hemisphere of the brain, but as a side effect would also tend to disadvantage the motor skills of the left hand and thus explain the link between handedness and hemispheric specialization. After Annett an extremely pronounced hemispheric dominance also implies disadvantages in cognitive or motor performance. The right- shift theory is controversial in the present research, so could not find a link between severe hemispheric dominance, and cognitive impairment about Crow and employees.