Neuroscience 2004 Abstract
| Presentation Number: | 986.21 |
|---|---|
| Abstract Title: | Mean field model of an orientation hypercolumn with conductance-based synapses. |
| Authors: |
Hertz, J. A.*1
; Aabo, T.2
; Ahmadi, M.1
; Lerchner, A.1,3
1Nordita, Copenhagen, Denmark 2Denmark, Blegdamsvej 17, 2100, 3Niels Bohr Inst., Blegdamsvej 17, 2100, |
| Primary Theme and Topics |
Sensory Systems - Vision -- Visual cortex: Functional organization and circuitry |
| Session: |
986. Visual Cortex: Orientation, Shapes, and Models Poster |
| Presentation Time: | Wednesday, October 27, 2004 1:00 PM-2:00 PM |
| Location: | San Diego Convention Center - Hall A-H, Board # DD19 |
| Keywords: | NOISE, VISUAL CORTEX, BURST, ORIENTATION |
It has been established that cortical visual neurons in vivo are in a state of high conductance due to large synaptic input. Nevertheless, little modeling of network dynamics has taken this finding into account. Here we try to begin to fill this gap by extending the mean field theory for a visual cortical hypercolumn presented at SFN 2003 (article at www.arxiv.org/abs/q-bio.NC/0403037) to include conductance-based synapses. Like that work, the theory can describe both population-average properties and neuron-to-neuron variation in responses and correlations. We find contrast-invariant tuning of the average responses, with fluctuations of a size compatible with experiments in the responses of individual neurons. The tuning of the firing irregularity, quantified by the Fano factor F, shows interesting orientation tuning properties, which depend on the synaptic conductance strengths, the post-firing reset level and the synaptic time constant. For experimentally reasonable choices of these model parameters, we find superpoissonian firing (F>1), with F maximal at the optimal orientation. This result is consistent with earlier experimental findings that the spike count variance was well-fit by a power-law function of the mean spike count with an exponent greater than 1. It can be understood in terms of the description of neuronal dynamics of Shelley et al in terms of the fluctuating `instantaneous reversal potential' (IRP): When the IRP remains above threshold for some time, the membrane potential can reach threshold and be reset several times, producing a burst of spikes. The average IRP and its fluctuations are both tuned, with lower values away from optimal orientation. Thus, excursions of the IRP above threshold are both rarer, leading to lower rates, and shorter, leading to shorter bursts and therefore smaller F at orientations away from optimal.
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2004 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2004. Online.
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