Pattern of cortical and thalamic connexions of the somatic sensory cortex

THE constituent cells of any architectonic subdivision in the somatic sensory and visual regions of the cerebral cortex respond to peripheral stimuli of a different nature from those which excite cells in other subdivisions. These individual differences have been thought to be principally dependent on afferent thalamic connexions or on cortical association connexions with other subareas1,2, but other factors may also be important, particularly because the various subareas also differ in their callosal connexions3,4, and because cortico-fugal influences may modify the activity of thalamic neurones5. As a consequence, in any interpretation of these functional differences it is advisable to take all the extrinsic connexions into account. The patterns of thalamic and cortical connexions of the somatic sensory cortex have been examined in the cat and monkey using experimental neurohistological techniques. The distribution of degenerating fibres, following lesions in the thalamus and in the somatic sensory and other cortical areas, has been studied by the Nauta method6 and with the electron microscope.