Attentional modulation of firing rate and synchrony in a model cortical network |
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Authors: | Calin Buia Paul Tiesinga |
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Institution: | (1) Computational Neurophysics Laboratory, Department of Physics & Astronomy, University of North Carolina at Chapel Hill, Campus Box 3255, Chapel Hill, North Carolina, 27599 |
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Abstract: | The response of a neuron in the visual cortex to stimuli of different contrast placed in its receptive field is commonly characterized
using the contrast response curve. When attention is directed into the receptive field of a V4 neuron, its contrast response
curve is shifted to lower contrast values (Reynolds et al., 2000). The neuron will thus be able to respond to weaker stimuli
than it responded to without attention. Attention also increases the coherence between neurons responding to the same stimulus
(Fries et al., 2001). We studied how the firing rate and synchrony of a densely interconnected cortical network varied with
contrast and how they were modulated by attention. The changes in contrast and attention were modeled as changes in driving
current to the network neurons.
We found that an increased driving current to the excitatory neurons increased the overall firing rate of the network, whereas
variation of the driving current to inhibitory neurons modulated the synchrony of the network. We explain the synchrony modulation
in terms of a locking phenomenon during which the ratio of excitatory to inhibitory firing rates is approximately constant
for a range of driving current values.
We explored the hypothesis that contrast is represented primarily as a drive to the excitatory neurons, whereas attention
corresponds to a reduction in driving current to the inhibitory neurons. Using this hypothesis, the model reproduces the following
experimental observations: (1) the firing rate of the excitatory neurons increases with contrast; (2) for high contrast stimuli,
the firing rate saturates and the network synchronizes; (3) attention shifts the contrast response curve to lower contrast
values; (4) attention leads to stronger synchronization that starts at a lower value of the contrast compared with the attend-away
condition. In addition, it predicts that attention increases the delay between the inhibitory and excitatory synchronous volleys
produced by the network, allowing the stimulus to recruit more downstream neurons.
Action Editor: David Golomb |
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Keywords: | Synchronization Synchrony modulation Delay modulation Attention |
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