15 Feb
1996
15 Feb
'96
6:58 p.m.
Below is the abstract of a forthcoming target article on:
THE DETECTION AND GENERATION OF SEQUENCES AS A KEY TO
CEREBELLAR FUNCTION. EXPERIMENTS AND THEORY
by V. Braitenberg, D. Heck and F. Sultan
This article has been accepted for publication in Behavioral and Brain
Sciences (BBS), an international, interdisciplinary journal providing
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____________________________________________________________________
THE DETECTION AND GENERATION OF SEQUENCES AS A KEY TO
CEREBELLAR FUNCTION. EXPERIMENTS AND THEORY
Valentino Braitenberg, Detlef Heck and
Fahad Sultan
Max-Planck-Institute for biological cybernetics
Spemannstr. 38
72076 Tuebingen
Germany
KEYWORDS: Cerebellum; motor control; allometric relation;
parallel fibers; synchronicity; spatio-temporal activity;
sequence addressable memory; cerebro-cerebellar interaction.
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.
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