Brachium pontis lesions in cats partly reproduce the cerebellar dysfunction of voluntary reaching movements.

The pontocerebellar pathway in the brachium pontis (BP), is known to convey signals from various cortical and subcortical visual structures to the cerebellum. Recently, a cortico-pontocerebellar pathway involving the BP has been implicated in the control of visually guided movements, on the basis of anatomical and physiological data. To further test this hypothesis, using behavioural methods, we studied the effects of a bilateral interruption of these projections in the BP, on 5 cats fully trained to perform a forepaw movement towards a moving target-light. The postoperative deficit consisted of an impairment in precision, with a strong tendency to over-reach and and increase in reaction time, contrasting with an unimpaired movement time. Although there was some initial recovery, performance soon stabilized with a permanent impairment in accuracy and reaction time. These results are discussed in relation to the various sensory signals processed at the pontine level and forwarded to the cerebellum, and compared with the effects of motor dysfunction of cerebellar origin.