Nuclei in which functionally identified spinothalamic tract neurons terminate

Abstract

The approximate level of termination of the axons of individual, functionally characterized spinothalamic tract neurons within the monkey thalamus was mapped by antidromic activation using a monopolar electrode which was moved in a systematic grid of tracks through the thalamus. The course of individual axons could be followed through several thalamic levels, and in a few cases branches to both the VPL nucleus and to the intralaminar nuclei were demonstrated. Most of the axons studied, however, projected just to the VPL_c or VPL_o nuclei. The spinothalamic tract cells that projected to the VPL_c nucleus included representatives of all known functional categories: low threshold, wide dynamic range, high threshold and “deep”. It is speculated that these different classes of spinothalamic projections could make contributions to such sensory modalities as touch, proprioception and pain.