Left hemisphere

The lateralization of brain function refers to how some neural functions, or cognitive processes tend to be more dominant in one hemisphere than the other. The medial longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. Although the macrostructure of the two hemispheres appears to be almost identical, different composition of neuronal networks allows for specialized function that is different in each hemisphere.

Lateralization of brain structures is based on general trends expressed in healthy patients; however, there are numerous counterexamples to each generalization. Each human’s brain develops differently leading to unique lateralization in individuals. This is different from specialization as lateralization refers only to the function of one structure divided between two hemispheres. Specialization is much easier to observe as a trend since it has a stronger anthropological history. The best example of an established lateralization is that of Broca's and Wernicke's Areas where both are often found exclusively on the left hemisphere. These areas frequently correspond to handedness however, meaning the localization of these areas is regularly found on the hemisphere corresponding to the dominant hand (anatomically on the opposite side). Function lateralization such as semantics, intonation, accentuation, prosody, etc. has since been called into question and largely been found to have a neuronal basis in both hemispheres.

To get a basic understanding of this complex issue it is easiest to first consider the left (LHS) and right (RHS) hemispheres as distinct but interacting entities. These interactions come in the form of both excitatory and inhibitory signals crossing the corpus callosum and other hemispheric bridges. As LHS and RHS each have unique interpretations of situations these signals allow for discussion and an ultimate decision to be made. This interaction is called hemispheric rivalry. This term is apt as both hemispheres are in conflict yet on the same team. In humans the reliance on both hemispheres is the basis of a number of functions including consciousness.

The LHS can be simplified to better understand its role in this rivalry. The LHS is centered around action and is often the driving force behind risky behaviors. This hemisphere heavily relies upon emotional input leading it to make brash and uncalculated decisions. These decisions should not be thought of as ill-conceived, rather illogical and raw.

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