RHS. The opposite asymmetry is observed in individuals such as violent offenders whose LHS is more distinct and pronounced than the RHS. The highest degree of symmetry between the hemispheres has been studied in veteran gang members. These individuals display an amazing propensity to act in extremely risky ways, yet inhibit themselves in the face of provocation to survive.
In gaining a fuller understanding of the interaction and function of cerebral hemispheres one must trace neural networks. The basis of the correlation of LHS with action and emotion is its connectivity with specialized parts throughout both hemispheres that play a role in those behaviors. Most notably LHS has been shown to have integral connections to insula and amygdala. Similarly, the association of RHS with inaction and calculation is tied to its extensive networks connecting to the anterior cingulate, orbitofrontal and prefrontal cortices. These specialized areas are implicated in the calculative and inhibitory processes of inaction and those related to delayed gratification. In studies looking at individuals with damaged LHS invariably the temporal lobe, insula and amygdala also sustained connectivity damage. Limiting the connectivity of such areas seriously limits the effectiveness by which they operate. This means that although logistically the LHS is not the ‘emotional’ hemisphere its connectivity with emotion related areas is crucial to their functioning. This same process implicates the RHS as the ‘calculative’ hemisphere, though logistically it is not.
The role of hemispheric rivalry has become a major talking point for those studying the generation of consciousness within the brain. Some believe the brain’s state of conflict is integrally linked to intelligence and genuine free will.
Failures of lateralization
Lateralization as a concept fails because the brain consistently updates, consolidates, shifts information between the hemispheres. In patients with damage to the LHS, functions traditionally associated with LHS were found predominantly in the RHS, most notably semantic choice. These results hold for those with RHS damage who show a similar amount of functionality in specific motor skills via new neural connections developed in the LHS after RHS damage. Amazingly these shifts continue to maximize brain potential even after extensive damage. In studies where patients incur LHS damage and functionality is shifted to RHS, damage of the same magnitude to the RHS causes RHS functionality to become split once more. This effect has been shown on a neuronal level as the stimulation of specific neurons in the RHS causes similar responses in both hemispheres as neuron clusters on each side enlarge to compensate for the initial stimulation. This points to a sort of equilibrium observed by the hemispheres.
The shift of info and neuron functionality between hemispheres should not be surprising, however, as it has been observed in individuals who have lost a sense. In these individuals, neurons, even those that are specialized, are semi-repurposed to compensate for the loss. For example: those who become blind after years of vision are able to repurpose specialized sections of their brain to have increased visualization and nonspecialization to aid in the efficiency of their other senses.
History of research on lateralization
One of the first indications of brain function lateralization resulted from the research of French physician Pierre Paul Broca, in 1861. His research involved the male patient nicknamed "Tan", who suffered a speech deficit (aphasia); "tan" was one of the few words he could articulate, hence his nickname. In Tan's autopsy, Broca determined he had a syphilitic lesion in the left cerebral hemisphere. This left frontal lobe brain area (Broca's area) is an important speech production region. The motor aspects of speech production deficits caused by damage to Broca’s area are known as expressive aphasia. In clinical assessment of this aphasia, it is noted that the patient cannot clearly articulate the language being employed.
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