Cerebellar Long Term Depression May Normalize Excitation of Purkinje Cells:
a Hypothesis.
Erik De Schutter
Born Bunge Foundation, University of Antwerp, B2610 Antwerp, Belgium
To appear in: Trends in Neurosciences
ABSTRACT
Long term depression (LTD) of parallel fiber (PF) synapses on
Purkinje cells is usually interpreted in the context of a specific
theory of motor learning by the cerebellum proposed by Marr, Albus
and Ito. Several arguments suggest that this theory may be false.
This paper presents a new hypothesis about the role of cerebellar LTD.
It is proposed that under physiological conditions LTD is autoinduced
by PF inputs. This proposal is based on the capacity of PF inputs
to generate calcium influx into the dendrite. LTD and other forms of
Purkinje cell synaptic plasticity are part of a local negative
feedback loop which prevents overstimulation of Purkinje cells by PF
inputs. The theory explains why it is difficult to induce LTD when
normal inhibition is present and why inhibitory inputs are potentiated
by the same conditions that can induce LTD of PF synapses.