Recovery functions of somatosensory evoked responses in man

Recovery functions of various components of the cerebral response evoked by a brief shock to median nerve showed that only component 5 was affected by a conditioning click, indicating that this component is only partially “non-specific” to a given modality of sensory stimulation.

Abstract

In human subjects the cerebral response evoked by a brief shock to median nerve is a complex potential lasting approximately 500 msec. Recovery functions of various components of the response were obtained in five subjects. A special-purpose analog computer extracted average evoked responses from the ongoing activity and separated conditioning and test responses which would normally overlap at brief interstimulus intervals. Comparison of these results with previous results in animal and man leads to the following analysis of somatosensory evoked response components: 1. Component 1, a brief diphasic potential appearing 20 msec after the stimulus, exhibits considerable recovery as early as 50 msec and is essentially recovered in 200 msec. Its recovery and other criteria indicate that it is a thalamo-cortical radiation response. 2. The behavior of component 2 during recovery suggests that it may be, or may contain, the classical primary positive response. 3. Response components designated 3 and 4 require at least 1 sec for complete recovery. Although the present results are inconclusive, a tentative hypothesis would relate 3 to the "association" response and 4 to the "secondary" response previously described in cat and monkey. 4. Component 5, a long-latency diphasic potential, requires several seconds for complete recovery. This and other characteristics of the response clearly relate it to the "non-specific" response or "V potential" previously described in man. 5. Click-shock recovery functions showed that only component 5 was affected by a conditioning click. The degree of subnormality was roughly half that for a conditioning shock, indicating that this component is only partially "non-specific" to a given modality of sensory stimulation.