Mechanism of thalamo -cortical projection and intracerebral association

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The mechanism of thalamo-cortical projection and intracerebral association system in the somatosensory pathways was studied in normal volunteers and cats. Cortical and subcortical somatosensory evoked potentials (SEPs) were recorded from the scalp, skull, dura mater, supra-and intra-cortex to evaluate the function of somatosensory pathways and primary sensory cortex (SI) in normal volunteers and cats. Topography of cortical SEPs over the scalp in normal controls during sleep stage revealed that cortical components (N20, P20, P22, P23 and N24) showed morphological changes and delayed peak latencies during sleep stage II and III/IV, and returned to the initial morphologies and peak latencies during REM sleep. These findings suggest that NREM sleep affects the origins of cortical SEPs which could be related to the synaptic function in the sensory cortex.Cortical and intracortical SEPs were recorded from the scalp, skull, dura mater, supra- and intra-cortex in cats. Morphologies and peak latencies of SEPs were essentially different between supra- and intra-cortical SEPs and scalp SEPs. Furthermore, cortical SEPs recorded from the medial, central and lateral SI areas with 3 to 5 mm intervals over the cortex were quite different morphologies and latencies in each electrode. These findings suggest that somatosensory pathways from the thalamus project not only to the SI areas but to frontal and parietal cortices.It is impossible to record cortical SEPs from both secondary sensory cortices (SII areas) in the cats.Neurotransmitters from the SI, motor and parietal cortices of the cats were analysed before, during and after the electrical stimulation of the radial nerve. The electrical stimulation of the radial nerve increased the acetylcholine release in the contralateral primary sensory area (SI) and motor area. Cholinergic transmission may be involved in the mechanism of cortical SEP generation.