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Here we present evidence that the cerebellar cortex in vivo specifically responds to sequential input to the granular layer, the main input site of the
cerebellar cortex. Ordered sequences of electrical stimuli were delivered through an array of stimulating electrodes in such a way, that an apparent movement
of the stimulus was produced. The parallel fiber population responses to sequential stimuli ‘moving‘ at 7 different velocities (0.1-0.7m/s) and in two different
directions (towards and away from the recording site) were measured extracellularly in the molecular layer. Population responses were maximal when the
stimulus moved towards the recording site at a velocity close to the conduction velocity of parallel fibers. Responses were significantly reduced when the
stimulus velocity was higher or lower. We conclude that the characteristic geometrical arrangement of parallel fibers enables the cerebellum to specifically
detect precise spatio- temporal activity patterns in the messy fiber system. These findings confirm earlier observations made in vitro and shed new light on the
functional interpretation of cerebellar anatomy. Together with recent findings suggesting that precise spatio-temporal activity patterns play a key role in
information processing in the neocortex, the results reported here are particularly important concerning the information exchange between the strongly
interconnected cerebellum and neocortex. (C) 2001 Elsevier Science B.V. All rights reserved.
