The Journal of Neuroscience, December 1, 2002, 22(23):10242-10250
Detectability of Excitatory versus Inhibitory Drive in an
Integrate-and-Fire-or-Burst Thalamocortical Relay Neuron Model
Gregory D.
Smith1 and
S. Murray
Sherman2
1 Department of Applied Science, College of William and
Mary, Williamsburg, Virginia 23187, and 2 Department of
Neurobiology, State University of New York, Stony Brook, New York
11794-5230
Although inhibitory inputs are often viewed as equal but opposite
to excitatory inputs, excitatory inputs may alter the firing of
postsynaptic cells more effectively than inhibitory inputs. This is
because spike cancellation produced by an inhibitory input requires coincidence in time, whereas an excitatory input can add
spikes with less temporal constraint. To test for such potential differences, especially in the context of the function of
thalamocortical (TC) relay nuclei, we used a stochastic
"integrate-and-fire-or-burst" TC neuron model to quantify the
detectability of excitatory and inhibitory drive in the presence and
absence of the low-threshold Ca2+ current,
IT, and the
hyperpolarization-activated cation conductance, Isag. We find that excitatory inputs are
generally superior drivers compared with inhibitory inputs in part
because spontaneous activity of a postsynaptic neuron is not required
in the case of excitatory drive. Interestingly, the presence of the
low-threshold Ca2+ current,
IT in a postsynaptic neuron allows
the robust detection of inhibitory drive over a certain range of
spontaneous and driven activity, a range that can be extended by the
presence of the hyperpolarization-activated cation conductance,
Isag. These simulations suggest a possible
reinterpretation of the role of inhibitory inputs, such as those to the thalamus.
Key words:
thalamus; inhibition; excitation; basal ganglia; neuron
model; driver; modulator
Copyright © 2002 Society for Neuroscience 0270-6474/02/222310242-09$05.00/0