Cellular processing of temporal information in medial vestibular nucleus neurons.
Quantitative descriptions of the cellular transformations from behaviorally relevant inputs into temporal patterns of firing are crucial for understanding information processing in systems of neurons and for incorporating biological properties of neurons into models of the neural control of behavior. To understand how neurons that mediate vestibulo-ocular behavior transform their inputs into temporal patterns of firing, we examined responses of medial vestibular nucleus (MVN) neurons to current injected intracellularly. MVN neurons recorded from avian brain slices fired spontaneously. Sinusoidal modulation of input current produced precisely sinusoidal modulation of firing rate. The transformation between input current and firing rate was remarkably linear: firing rate scaled linearly as a function of current amplitude, and the responses to steps of input current were predicted accurately from the linear superposition of responses to sinusoidal modulation of input current. Over the physiological range of head movement frequencies, from 0.1 to 10 Hz, peak-to-peak modulation of firing rate was relatively constant or increased slightly in most neurons. In contrast, when hyperpolarizing current was used to keep neurons below threshold for action potentials, the frequency response of the membrane potential behaved like a low-pass filter. These results imply that the membrane conductances that are active when MVN neurons fire compensate for the low-pass characteristics of the membrane to allow faithful transmission of high frequency head movement signals.
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