Response properties of spinal neurons projecting to midbrain or midbrain-thalamus in the monkey

Response and receptive field properties were determined for 24 spinal neurons backfired from midbrain or midbrain-thalamus in the anesthetized monkey. Recording sites were located in laminae I (11 cells), IV (6), V (6) and VI (1) in the lumbosacral spinal cord. The mean axonal conduction velocity of cells projecting to midbrain was significantly less than that of cells projecting to midbrain-thalamus. Cells backfired only from midbrain had complex excitatory receptive fields whereas those projecting to midbrain-thalamus had excitatory receptive fields confined to a single limb. Cells in both populations had complex inhibitory receptive fields.