Nuclei in which functionally identified spinothalamic tract neurons terminate.

The approximate level of termination of the axons of individual, functionally characterized spinothalamic tract neurons within the monkey thalmus 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 VPLc or VPLo nuclei. The spinothalamic tract cells that projected to the VPLc nucleus included representative 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.