Download Cerebellar cortical neurons exhibit bimodality in freely moving animals

Cerebellum
CEREBELLAR CORTICAL NEURONS EXHIBIT BIMODALITY IN FREELY
MOVING ANIMALS
Iddo Lev1, Gilad Jacobson2,3, Yosef Yarom2,3, Dana Cohen1
1
The Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat-Gan 52900, Israel.
2
Department of Neurobiology, Life Science Institute and 3The Interdisciplinary Center for Neural
Computation, Edmond Safra Campus, Jerusalem 91904, Israel.
The information content transferred by neurons is encoded in their time dependent firing
patterns. Some neurons exhibit bimodal firing patterns in which neurons alternate between
periods of high firing rates (up state) to periods of quiescence (down state). Intracellular
recordings from Purkinje cells in cerebellar slices showed that the bimodal firing pattern
reflects a bistable membrane potential. Recently it has been shown that the membrane
potential of Purkinje cells in intact, anesthetized brain is also bistable. This finding was
challenged by a report claiming that Purkinje cells in awake animals are continuously in
their up state and quiescent periods of Purkinje cells could not be detected in awake
animals.
We reexamined this issue by implanting microwire arrays into the cerebellar cortex and
recording activity of cerebellar cortical neurons while animals walked freely in their home
cages. An array of 32 isonel coated tungsten microwires (35 microns in diameter) was
implanted into the posterior part of the cerebellar vermis. After about 10 days of recovery,
we observed high levels of spontaneous activity. The majority of the clearly sorted single
units, displayed epochs of high firing rates followed by prolonged quiescent periods. For
the identification of Purkinje cells we compared these recordings with recordings under
isoflorane anesthesia of the same animals. Although, the transition from anesthetized to
awake state was accompanied by an increase in firing rate the bimodal pattern was clearly
observed.
These results show beyond a doubt that cerebellar cortical neurons recorded chronically in
freely moving animals, exhibit bimodal firing patterns.