Sensory Cortex and cerebral plasticity

Sensory surfaces

Various techniques of studies make it possible to establish a true chart of the surfaces of the Cerveau dedicated to the Motricité and the direction. It is noted that same a lesion cerebral Cortex always involves the same sensory loss. The case study private clinics, baptized Neuropsychology, is thus a technique used to establish a geographical map of the sensory surfaces on the level of the cortex. One also uses the cerebral Imagerie which makes it possible to locate the active zones of the brain during a task, as well as the observation of the behavioral answers to electric or magnetic stimulations of the cortex. One can thus distinguish from the visual surfaces (occipital, i.e with the back of the cerebral hemispheres), of the auditive surfaces (temporal, i.e under the temples), of the somatosensorielles surfaces responsible for the to touch and the Proprioception (perception of the position of the body in space), of the vestibular surfaces, responsible for the control of the balance, the surfaces related to the Olfaction…

At the man, the somatosensorielles cortical zones are not proportional to the size of the members. In fact, plus a body zone is sensitive (i.e able to discriminate two contiguous tactile stimuli) more its cortical representation is important. For example, the cortical representation of the Doigt S (left most sensitive at the man) mobilizes much more neurons than those of the Cuisse S or Dos. Of this Somatotopie (representation of the body in the central nervous system) it is possible to draw a sensitive Homonculus: a deformed representation of the body defining a " man sensible". In a similar way, the central part of the field of vision (the Fovea) is surreprésentée in the visual Cortex, and them bands of auditive frequency S most useful (for example, for the sounds used in the Parole between 500 and 4000 Hz) are surreprésentées in the auditive cortex.

cerebral Plasticity

The installation of the neural networks is far from being finished with the Naissance of an individual. It is at the man towards the 18 years age that his completed development is considered. But it should be known that the cerebral Cortex is malleable : according to whether one stimulates or not a Organe, its representation on the level it cortex will be more or less important. It is noticed that at the people having undergone the occlusion of the left eye, the right eye at the end of a certain time will take as much place than the two eyes before this occlusion. In the same way when a direction is voluntarily stimulated, like hearing at the tuners of piano or the touch in a violonist. The disuse of a faculty can on the contrary involve its regression at the cerebral level. In certain cerebral cases of Tumor S with slow development, this cerebral plasticity makes it possible to maintain intact all the functions until a very advanced stage of the disease (one can realize whereas 20% of the cerebral hemispheres are nonfunctional). This plasticity is primarily due to the modifications of connections between neurons (synaptic modifications ) which are carried out throughout the life. However there exists also a Neurogenèse (formation of neurons starting from original cells) in certain not-cortical zones of the brain (as in the hippocampus).

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