Coding of vibration by neurones 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 characteristics of neurones in a first relay, the dorsal column nuclei (nuclei gracilis et cuneatus and the nucleus cuneatus externus), were studied electrophysiologically by recording responses from individual neurones to mechanical stimulation of skin and deep tissue.Of 140 units 84 were cutaneous neurones. The remainder were tap- and deep-neurones. Tap-neurones were activated by sharp brief taps. Activity in deep-neurones was comparable to joint and tendon receptors but not to muscle spindles. Thirty-four cutaneous neurones were vibration sensitive neurones, 36 were slowly adapting neurones and 14 neurones were rapidly adapting and fast habituating cells. Vibration sensitive neurones were most sensitive to 200 to 500 Hz. Frequencies above 100 Hz elicited phase coupled responses.Within the nn. gracilis et cuneatus 61 were cutaneous neurones, 13 were deep-neurones and 7 were tap-cells. Within n. cuneatus externus 17 were cutaneous units, 21 were deep-neurones and 11 were tap-neurones. No vibration sensitive neurones were found within n. cuneatus externus. This means that coding for vibration is represented in the nn. gracilis et cuneatus.Abbreviations CE n. cuneatus externus - DCN dorsal column nuclei - GC n. gracilis et cuneatus - HC Herbst corpuscle - PH phasic and habituating - Imps./s Impulses per second - INTH interval histogram - PSTH peristimulus time histogram - PHASE Phase histogram - RF receptive field - SA slowly adapting - Vec. vector strength