Magzoub, Mohammed Salah Eldin Mohammed Ali; (1996) The representation of respiratory movements in the inferior olive. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

It has been previously proposed that the inferior olive (IO) acts as a 'comparator' signalling to the cerebellum differences (errors) between signals conveying the command for movement from 'higher motor centres' and the activity these signals evoke at spinal 'centres' which also are in reciept of peripheral inputs (Oscarsson, 1973). Validation of this hypothesis has been hindered by the lack of direct access to the command signals. A review of the literature revealed that the respiratory system, as a source of centrally initiated automatic movements, offers a unique opportunity for studying both the command and outcome for a naturally occurring movement. The experiments in the first section of the thesis reinvestigate the interactions between the central respiratory drive and segmental (chest wall) reflexes. Muscle afferent activity was also monitored in intercostal nerve filaments to define proprioceptive inputs to the spinal cord and brainstem during artificial ventilation. Against this background the IO was explored by extracellular recording to seek evidence of central and peripheral-related respiratory activities. Three principal types of respiratory related activities were encountered in the dorsal accessory olive (DAO); 1), respiratory phased, mass activity; 2), respiratory phased, low frequency activity; 3), respiratory pump locked activity. The spatial location of these activities was found to correspond to a narrow, longitudinal strip in the DAO representing the segmental projection of the spino-olivary neurones located in the thoracic spinal cord, as identified anatomically by Matsushita et al. (1992). The source of these activities was investigated by cold block of the cervical spinal cord at C3. Whereas the central respiratory activity was abolished in spinal motoneurones, it persisted in the DAO indicating that the DAO receives a phasic respiratory input of supraspinal origin. Lowering the CO2 while holding the mechanical conditions in the thorax constant, resulted in changes in the olivary discharge, further indicating that the central command is fed to the olive, thus supporting the view that the olivary neurones act as a comparator signalling differences between the command for movement and the outcome.

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