Input-driven components of spike-frequency adaptation can be unmasked in vivo
Tim Gollisch & Andreas V. M. Herz
Journal of Neuroscience 25: 7435-7444 (2004)
Abstract
Spike-frequency adaptation affects the response characteristics of
many sensory neurons, and different biophysical processes
contribute to this phenomenon. Many cellular mechanisms underlying
adaptation are triggered by the spike output of the neuron in a
feedback manner (e.g., specific potassium currents that are
primarily activated by the spiking activity). In contrast, other
components of adaptation may be caused by, in a feedforward way,
the sensory or synaptic input, which the neuron receives. Examples
include viscoelasticity of mechanoreceptors, transducer adaptation
in hair cells, and short-term synaptic depression. For a
functional characterization of spike-frequency adaptation, it is
essential to understand the dependence of adaptation on the input
and output of the neuron. Here, we demonstrate how an input-driven
component of adaptation can be uncovered in vivo from recordings
of spike trains in an insect auditory receptor neuron, even if the
total adaptation is dominated by output-driven components. Our
method is based on the identification of different inputs that
yield the same output and sudden switches between these inputs. In
particular, we determined for different sound frequencies those
intensities that are required to yield a predefined steady-state
firing rate of the neuron. We then found that switching between
these sound frequencies causes transient deviations of the firing
rate. These firing-rate deflections are evidence of input-driven
adaptation and can be used to quantify how this adaptation
component affects the neural activity. Based on previous knowledge
of the processes in auditory transduction, we conclude that for
the investigated auditory receptor neurons, this adaptation
phenomenon is of mechanical origin.
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