Abstract
The stimulation of a single neuron in the rat somatosensory cortex can elicit a behavioral response. The probability of a behavioral response does not depend appreciably on the duration or intensity of a constant stimulation, whereas the response probability increases significantly upon injection of an irregular current. Biological mechanisms that can potentially suppress a constant input signal are present in the dynamics of both neurons and synapses and seem ideal candidates to explain these experimental findings. Here, we study a large network of integrate-and-fire neurons with several salient features of neuronal populations in the rat barrel cortex. The model includes cellular spike-frequency adaptation, experimentally constrained numbers and types of chemical synapses endowed with short-term plasticity, and gap junctions. Numerical simulations of this model indicate that cellular and synaptic adaptation mechanisms alone may not suffice to account for the experimental results if the local network activity is read out by an integrator. However, a circuit that approximates a differentiator can detect the single-cell stimulation with a reliability that barely depends on the length or intensity of the stimulus, but that increases when an irregular signal is used. This finding is in accordance with the experimental results obtained for the stimulation of a regularly-spiking excitatory cell.
Highlights
A classical method used in neuroscience to understand cortical circuits is to determine how single neurons respond to a controlled sensory stimulus
We show that a basic excitatory-inhibitory circuit can be used to approximate the differentiator, and demonstrate that the response of this so-called differentiator network readout is in several key aspects similar to the behavioral response observed in the experiments in ref. [6]
Taking into account the estimated neuron density in the barrel cortex [7], a sphere with a radius of 200μm contains about N = 2600 neurons, which we take as the network size
Summary
A classical method used in neuroscience to understand cortical circuits is to determine how single neurons respond to a controlled sensory stimulus. In the case that the stimulation affects only a single neuron, the outcome of the unconventional and technically challenging reverse physiology experiments are striking: stimulating a single neuron in the motor cortex can evoke a whisker movement [3], and single-cell stimulation in the barrel cortex—but not in the thalamus—leads to a weak but statistically significant behavioral response [4,5,6]. This contradicts prevailing hypotheses that relevant signals can only be encoded in the activity of large neural populations
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