CODING OF VIBRATION BY NEURONS OF THE DORSAL COLUMN NUCLEI IN THE PIGEON

Whereas the function of mechanoreceptors is well known in birds there are no detailed investigations of central processing. Therefore the ch aracteristics of neurones in a first relay, the dorsal column nuclei ( nuclei gracilis et cuneatus and the nucleus cuneatus externus), were s tudied electrophysiologically by recording responses from individual n eurones to mechanical stimulation of skin and deep tissue. Of 140 unit s 84 were cutaneous neurones. The remainder were tap- and deep-neurone s. Tap-neurones were activated by sharp brief taps, Activity in deep,n eurones was comparable to joint and tendon receptors but not to muscle spindles. Thirty-four cutaneous neurones were vibration sensitive neu rones, 36 were slowly adapting neurones and 14 neurones were rapidly a dapting and fast habituating cells. Vibration sensitive neurones were most sensitive to 200 to 500 Hz. Frequencies above 100 Hz elicited pha se coupled responses. Within the nn. gracilis et cuneatus 61 were cuta neous neurones, 13 were deep-neurones and 7 were tap-cells. Within n. cuneatus externus 17 were cutaneous units, 21 were deep-neurones and 1 1 were tap-neurones. No vibration sensitive neurones were found within n. cuneatus externus. This means that coding for vibration is represe nted in the nn. gracilis et cuneatus.