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Integrative Versus Delay Line Characteristics of Cerebellar Cortex

Published online by Cambridge University Press:  18 September 2015

W.A. MacKay  and
J.T. Murphy
W.A. MacKay
Affiliation:
Department of Physiology, University of Toronto, Toronto, Canada
J.T. Murphy*
Affiliation:
Department of Physiology, University of Toronto, Toronto, Canada
*
Department of Physiology, Medical Sciences Building, University of Toronto, Toronto, Ont. M5S 1A8, Canada
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In order to determine which of two general models (“tapped delay line” or “integrator”) provides a more accurate description of mammalian Purkinje cell (P-cell) activation by natural stimulation, the spatial and temporal characteristics of a population of neurons in cerebellar cortex responsive to small controlled stretches of forelimb muscles were examined in awake, locally anesthetized cats. Stretch of a single wrist muscle excited P-cells over a distance of about 1 mm in the long axis of a folium, a span which is at most half the length of parallel fibers. Both granule cells and molecular layer interneurons were excited over a wider zone than P-cells.

Furthermore, P-cells across a response zone all fired on the average at the same time, as determined by computing peristimulus cross-interval histograms from pairs of simultaneously recorded neurons. Consistent delays could only be demonstrated in the minimal response latencies as measured from peristimulus time histograms. These delays, however, were longer than could be ascribed to parallel fiber conduction velocity.

No evidence, therefore, was found in cat cerebellum to support the “tapped delay line” model, which postulates the successive activation of P-cells as an excitatory volley travels along a parallel fiber beam. Instead, an integrative mode of operation seems to predominate: a relatively wide substratum of activated granule cells simultaneously activates a narrower focus of P-cells centrally situated with respect to the granule cell population. The role of inhibitory interneurons in promoting the “integrator” model is discussed.

Type
Research Article
Information
Canadian Journal of Neurological Sciences , Volume 3 , Issue 2 , May 1976 , pp. 85 - 97
Copyright
Copyright © Canadian Neurological Sciences Federation 1976

References

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