Sensory representation of the wing in the spinal dorsal horn of the pigeon.

Somatotopic organization and response characteristics were examined in 234 dorsal horn neurons in the cervical enlargement of the spinal cord of anesthetized pigeons. Neurons located in the nucleus proprius (laminae III-V) were activated by light mechanical stimulation (movement of feathers) of cutaneous receptors. Both slowly adapting and rapidly adapting responses were observed, the latter being more numerous. Although most neurons responded to vibratory stimuli, an input from Pacinian-like receptors (Herbst corpuscles in birds) has still to be demonstrated. There was no evidence of an input from high-threshold receptors (nociceptors). Latencies to electrical stimulation of the receptive field suggest a contribution of large myelinated afferent fibers only. Neurons in the avian Clarke's column (within lamina V of the cervical enlargement) were activated by proprioreceptor stimulation. Receptive fields were usually small but larger on proximal parts of the wing (forearm and arm) than on distal parts (hand with fingers). There was a distinct topographic organization of receptive fields. Rostral parts of the wing (prepatagium, alula) were represented rostrally (C12, C13) and caudal parts (secondaries) caudally (C14). Furthermore, distal and ventral parts of the wing were represented medially and proximal and dorsal parts laterally. Despite its very specialized function (bird flight) the somatotopic representation of the wing in the spinal dorsal horn is very similar to that of the forelimb of mammalian species.