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An emergent model of orientation selectivity in cat visual cortical simple cells
D C Somers1, S B Nelson, M Sur
1Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139, USA.
Summary
Local intracortical excitation, not inhibition, generates orientation selectivity in the visual cortex. This emergent property arises from recurrent feedback circuitry, explaining experimental data and offering a unified model of inhibition roles.
Area of Science:
- Neuroscience
- Computational Neuroscience
- Visual System Research
Background:
- Visual cortical neurons exhibit orientation selectivity, unlike their LGN inputs.
- Existing models of orientation selectivity conflict with experimental findings.
Purpose of the Study:
- To present a computational model of cat primary visual cortex (area 17) layer IV.
- To demonstrate the role of local intracortical excitation in generating orientation selectivity.
Main Methods:
- A 1:4 scale computational model of a visual cortex region was developed.
- The model simulated neuronal responses to visual stimuli, incorporating excitation and inhibition.
Main Results:
- Model cortical cells showed sharp orientation selectivity, driven by recurrent excitation.
- Orientation tuning was independent of stimulus contrast and persisted when ON-type subfields were silenced.
- The model reconciled conflicting data from inhibitory blockade experiments.
Conclusions:
- Local intracortical excitation is the dominant source of orientation-selective input.
- Orientation selectivity is an emergent property of cortical feedback circuitry.
- Intracortical inhibition balances excitation at the columnar level to maintain selectivity.