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Next: GabbianiMetzner, Wessel Up: No Title Previous: DobrunzStevens, and

duLac: Cellular processing of temporal information in the vestibulo-ocular reflex

UCSF

How do the ensemble of ionic conductances in neurons contribute to their ability to encode behaviorally relevant information? Neurons contain a variety of intrinsic membrane channels in addition to those required to generate and repolarize action potentials. Presumably the nature and distribution of these channels in different types of neurons are governed by the behavioral tasks that each neuron subserves. I have been studying ionic mechanims of signal transformations in neurons that participate in the vestibulo-ocular reflex (VOR). The VOR enables clear vision during head movements by producing eye movements that are equal in amplitude and opposite in direction to head movements. This simple behavior is precise and linear over a wide range of head movement frequencies (from about 0.1 to 10 hz) and can be modulated over both short and long timescales. 20

Intracellular recordings from brainstem slices reveal that vestibular neurons have a number of membrane and firing properties that make them well-suited for mediating the VOR. First, vestibular neurons fire regularly and spontaneously, allowing them to encode both increases and decreases in input signals. Second, the transformation between input current and modulations in firing rate (ie spike encoding) is remarkably linear and precise over the behaviorally relevant range of head movement frequencies. Third, at least one type of ion channel (a calcium-activated potassium channel) controls the gain of spike encoding without affecting linearity or dynamics, suggesting that modulation of this channel could underlie short and/or long term modulation of the VOR. These findings raise the following questions:

  1. How do non-linear conductances combine to make a linear spike encoder?
  2. does it make sense to postulate that the nervous system encodes information in modulations of firing rate?
  3. What can we learn about cellular contributions to behaviorally relevant encoding of information by comparing the encoding mechanisms of vestibular neurons with those of other neurons (such as hippocampal or cortical pyramidal cells)?


next up previous
Next: GabbianiMetzner, Wessel Up: No Title Previous: DobrunzStevens, and

Tony Zador
Tue Oct 22 16:34:57 PDT 1996