ABSTRACT
The primary somatosensory cortex is composed of cytoarchitectonic areas 3a, 3b, 1 and 2. Within each of these areas there is a complete topographic representation of the body, but neurons within each of them respond to different submodalities of somatic inputs. The somatic sensory system has provided an admirable model for studies of plasticity in the mature brain. The degree to which the nervous system shows plasticity has been one of the seminal questions that has driven man’s curiosity about the brain. The diffuse extrathalamic cortical regulatory systems involve the cortical projections of the ventral tegmental system, the raphe nuclei, locus coeruleus and the pontine and basal forebrain systems. The precise function of these systems is controversial, but the noradrenergic locus coeruleus (LC) seems to be gaining favor as a system that controls vigilance, or attention. Activation of the LC releases noradrenalin at sites throughout all of the cerebral cortex and most of the rest of the brain.
