Dorsal horn cells in spinal and in freely moving rats

Rat spinal-cord dorsal horn was explored with microelectrodes and shown to contain, as in the cat, three horizontal laminae. The cells in the most dorsal lamina had small cutaneous receptive fields; in the middle zone, the cutaneous receptive fields expanded markedly; in the most ventral region, cells were encountered which responded to passive movement of the leg. Some differences between cat and rat were noticed. A method was developed by which recordings could be made from single cells in rat cord while the animal was freely moving. Responses of single cells to a fixed afferent volley were shown to vary with the behavioral state of the animal. Part of the variability could be attributed to impulses descending from the head and not to movement of either the stimulating or recording electrodes or to the interaction of local afferents. An anthropomorphic interpretation of the results would be that the direction of the animal's attention was affecting the response of cord cells receiving cutaneous afferent impulses.