Abstract
Summary
Rats were used to study the influence of dorsal column stimulation on the activity of those spinal cord cells which transmit peripheral excitations to the somesthetic thalamus via the spinothalamic tract (STT) and the spinocervicothalamic pathway (SCP). Since both of these paths terminate in the thalamic SII, separate transection of one of them left the other as the sole path of afferent excitations for reaching the thalamic recording site. This experimental design eliminated the uncertainty about the anatomical identity of the spinal cord transmission cells studied in experiments reported previously. Single electrical pulses applied to the gracile fasciculus of the dorsal columns inhibited the transmission of afferent activity via the SCP and STT when these pulses preceded the initiation of the afferent activity by 15–200 msec. This inhibition is most likely the basis for analgesia induced in patients by electrical stimulation of their dorsal columns. Since, however, a delayed postexcitatory inhibition has been recently observed to exist at the first synaptic relay of several sensory modalities, it is unlikely that the inhibition which exists at the T-cells of the STT represents a unique mechanism for the coding of pain. It is more reasonable to think that such a coding takes place at the thalamic level.
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