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THE DETECTION AND GENERATION OF SEQUENCES AS A KEY TO CEREBELLAR FUNCTION. EXPERIMENTS AND THEORY

Braitenberg, Valentino , Heck , Detlef and Sultan, Fahad (1997) THE DETECTION AND GENERATION OF SEQUENCES AS A KEY TO CEREBELLAR FUNCTION. EXPERIMENTS AND THEORY.

Short Abstract:

Starting from macroscopic and microscopic facts of cerebellar histology, we propose a new functional interpretation which may elucidate the role of the cerebellum in movement control. Briefly, the idea is that the cerebellum is a large collection of individual lines (Eccles' "beams") which respond specifically to certain sequences of events in the input and in turn produce sequences of signals in the output. We believe that the sequence in - sequence out mode operation is as typical for the cerebellar cortex as the transformation of sets into sets of active neurons is typical for the cerebral cortex, and that both the histological differences between the two and their reciprocal functional interactions become understandable in the light of this dichotomy. The response of Purkinje cells to sequences of stimuli in the mossy fiber system was shown experimentally by Heck on surviving slices of rat and guinea pig cerebellum. Sequential activation of a row of eleven stimulating electrodes in the granular layer, imitating a "movement" of the stimuli along the folium, produces a powerful volley in the parallel fibers which strongly excites Purkinje cells, as evidenced by intracellular recording. The volley, or "tidal wave" has maximal amplitude when the stimulus moves towards the recording site at the speed of conduction in parallel fibers, and much smaller amplitudes for lower or higher "velocities". The succession of stimuli has no effect when they "move" in the opposite direction. Synchronous activation of the stimulus electrodes also had hardly any effect. We believe that the sequences of mossy fiber activation which normally produce this effect in the intact cerebellum are a combination of motor planning, relayed to the cerebellum by the cerebral cortex, and information about ongoing movement, reaching the cerebellum from the spinal cord. The output elicited by the specific sequence to which a "beam" is tuned may well be a succession of well timed inhibitory volleys "sculpting" the motor sequences so as to adapt them to the complicated requirements of the physics of a multi-jointed system.

Long Abstract:

Starting from macroscopic and microscopic facts of cerebellar histology, we propose a new functional interpretation which may elucidate the role of the cerebellum in movement control. Briefly, the idea is that the cerebellum is a large collection of individual lines (Eccles' "beams") which respond specifically to certain sequences of events in the input and in turn produce sequences of signals in the output. We believe that the sequence in - sequence out mode operation is as typical for the cerebellar cortex as the transformation of sets into sets of active neurons is typical for the cerebral cortex, and that both the histological differences between the two and their reciprocal functional interactions become understandable in the light of this dichotomy. The response of Purkinje cells to sequences of stimuli in the mossy fiber system was shown experimentally by Heck on surviving slices of rat and guinea pig cerebellum. Sequential activation of a row of eleven stimulating electrodes in the granular layer, imitating a "movement" of the stimuli along the folium, produces a powerful volley in the parallel fibers which strongly excites Purkinje cells, as evidenced by intracellular recording. The volley, or "tidal wave" has maximal amplitude when the stimulus moves towards the recording site at the speed of conduction in parallel fibers, and much smaller amplitudes for lower or higher "velocities". The succession of stimuli has no effect when they "move" in the opposite direction. Synchronous activation of the stimulus electrodes also had hardly any effect. We believe that the sequences of mossy fiber activation which normally produce this effect in the intact cerebellum are a combination of motor planning, relayed to the cerebellum by the cerebral cortex, and information about ongoing movement, reaching the cerebellum from the spinal cord. The output elicited by the specific sequence to which a "beam" is tuned may well be a succession of well timed inhibitory volleys "sculpting" the motor sequences so as to adapt them to the complicated requirements of the physics of a multi-jointed system.

Keywords:	Cerebellum; motor control; allometric relation; parallel fibers; synchronicity; spatio-temporal activity; sequence addressable memory; cerebro-cerebellar interaction
Subjects:	Neuroscience: Behavioral Neuroscience Biology: Behavioral Biology Psychology: Cognitive Psychology Neuroscience: Computational Neuroscience Psychology: Learning and Memory Neuroscience: Neuroanatomy Neuroscience: Neural Modelling Neuroscience: Motor Function Neuroscience: Neuropsychology Psychology: Psychobiology
ID code:	bbs00000436
Deposited by:	Valentino Braitenberg on 01 May 2001