Cortical responses to paired stimuli applied peripherally and at sites along the somato‐sensory pathway

Abstract

SUMMARY1. Experiments have been performed on animals anaesthetized with various anaesthetics to determine the responsiveness of the cortex to the second of a pair of identical stimuli applied at three sites along the sensory pathway, i.e. to the periphery, the medial lemniscus and to thalamocortical fibres.2. It has been found that in deeply anaesthetized animals the mass response recorded from the cerebral cortex to the second of a pair of peripheral or lemniscal stimuli became reduced in size if the interval between the stimuli was 30-500 msec. If the interval was less than 30 msec for peripheral stimuli or between 10 and 30 msec for lemniscal stimuli responses were not obtained to the second stimulus. This was found to be a basic pattern which could be modified in animals less deeply anaesthetized. In these animals, periods of relatively increased responsiveness were seen after peripheral stimulation.3. The post-synaptic responses recorded from the ventrobasal thalamus showed the same behaviour to the second of a pair of peripheral stimuli as did the cortex both as regards size and latency of the responses.4. The post-synaptic responses recorded from the cuneate nucleus rarely showed any reduction in size unless the separation between the stimuli was 10 msec or less; even at intervals as low as 3 msec there was no increase in the latency of the response.5. When a pair of stimuli were applied to thalamocortical fibres, a different pattern of cortical responsiveness was found. At the time the cortical response to stimulation at pre-thalamic sites was reduced or abolished, the response to stimulation at post-thalamic sites was unaltered or increased in size.

The functional status and columnar organization of single cells responding to cutaneous stimulation in neonatal rat somatosensory cortex S1.

“…With regard to 7 day old S I topographical arrangement, the relative positions of somatotopically organized columns compares favourably with the projection found in the adult (Woolsey & Le Messurier, 1948;Angel, 1967;Carter, Holmes & Houchin, 1969;Welker, 1971). Furthermore the relative amount of cortex devoted to handling information from particular areas of skin appears to be similar at the two ages.…”

Temporal and spatial integration in the rat SI vibrissa cortex

“…Several subsequent studies have shown that one effect of this is a diminution in the responsiveness of cortical cells following a punctate cutaneous stimulus, displacement of a single facial vibrissa, and/or electrical shock to a peripheral nerve (2,12,18,43). This decreased responsiveness is seen as a reduction in the number of unit discharges elicited by the second of two equally intense stimuli and is most pronounced during the lo-20 ms after the first stimulus.…”

Impaired intracortical inhibition in the primary somatosensory cortex in focal hand dystonia

“…Inhibition of the somatosensory system follows excitation, which can be shown in physiological studies with somatosensory‐evoked potential (SEP) technique using a peripheral paired‐pulse paradigm. In both normal animals and humans, a conditioning (preceding) stimulus induces suppression of SEP amplitudes evoked by a following test stimulus 7–9. This inhibitory action is believed to be important in preserving the temporal separation of serially administered stimuli and in enhancing the contrast among them.…”