[Transcommissural afferent projections of the lemniscal and spino-reticulo-thalamic systems].

In cats with section of classic, contralateral somatosensory pathways of the fore-leg at the midbrain level an instrumental defensive reflex "to this leg" can be elaborated. This fact suggests that the intact ipsilateral afferent somatosensory pathways of the brain-stem transmit kinsthetic excitations. The electrophysiological study (acute experiments under nembutal anesthesia) of somatosensory projections of the fore-leg, contralateral to the midbrain section, revealed bilateral evoked responses in the somato-sensory cortical areas with a latency of 18-20 msec. These responses evidence bilateral afferent projections of the ipsilateral part of the spinoreticulo-thalamic system. They constitute the functional basis for the formation of this conditioned instrumental defensive reflex. The lemniscal system as well as the ipsilateral part of spino-reticulo-thalamic system send bilateral afferent projections to the somatosensory structures of the brain.