Baker, Simon Charles; (1995) The control of transmission in spino-olivo-cerebellar pathways. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Climbing fibre responses from the thorax were recorded from the a, b and c2 zones. Evidence for a rostro-caudal somatotopic organisation of the a and c2 zones is discussed, with rostral axial structures represented in more caudal lobules of the anterior lobe and in the more rostral folia of the c2 zone in the paramedian lobule of the posterior lobe. In the paralysed decerebrate preparation, transmission in spino olivo-cerebellar paths (SOCPs) to the ipsilateral b zone from the thorax was consistently inhibited during the inspiratory phase of the central respiratory cycle and more weakly inhibited during the late expiratory phase. The phasic inhibition corresponds to the phases of active respiratory movement. The excitability of the ipsilateral b zone SOCP from the thorax was also modulated by phasic afferent activity generated by passive inflation and deflation of the thorax during artificial ventilation. The polysynaptic segmental intercostal to intercostal reflex in both inspiratory and expiratory nerves was phasically modulated during the respiratory cycle with prominent inhibition during inspiration. A model of the segmental neural network is proposed that could also modulate activity in the segmental relays of ascending pathways. The phasic respiratory modulation of excitability of these pathways is reflected in the excitability of the inferior olive. Both spontaneous complex spike discharge and the amplitude of the olivary reflex are reduced during the inspiratory phase in the thoracic microzone of the ipsilateral b zone in the paralysed decerebrate preparation. Phasic modulation of simple spike discharge was observed in some Purkinje cells in the b zone during the respiratory cycle, but was not systematically investigated. The amplitude of the initial spike and secondary spikes of the climbing fibre response and plateau potentials were not significantly influenced by the phase of the respiratory cycle. The results are discussed in relation to the hypothesis that the olivary discharge represents a motor error signal. A distinction is made between afferent activity signalling deviation of actual from intended movement that can be used for feedback correction within an ongoing movement and a perturbation or deviation that requires correction by an additional movement or a change in motor strategy. The climbing fibre response is identified with the latter motor performance error.

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