[Low-threshold mechanisms and pathways of corticofugal activation]

In chronic experiments of alert cats, moderate electrical stimulation of different points on the lateral cortical surface led to activation of different cerebral areas. Both the high-threshold and the low-threshold points were revealed in the sensorimotor cortex and in the Ep field of auditory area. The latter had as low a threshold of the activation response as the points within the mesencephalic RF and the thalamic CM, VPL and GM. In the morphological aspect, projections from the auditory Ep field to the thalamic intralaminar nuclei and to the brain stem RF, were revealed. Major projections spread from the dorsal part of the Ep field to the lateral tegmentum. The data obtained seem to provide better comprehending of the mechanisms for corticofugal activation. The functional role of the low-threshold loci in the cortex can involve triggering of unspecific apparatus of activation with a graduated volley which controls its excitation in accordance with biological significance of analysed signals.