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Subthreshold facilitation and suppression in primary visual cortex revealed by intrinsic signal imaging
1Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139, USA. ljtoth@mit.edu
Summary
Neurons in the primary visual cortex (area 17) exhibit surround modulation, where stimuli outside the main receptive field influence neural responses. This interaction, dependent on contrast, is crucial for higher-level visual processing like perceptual pop-out.
Area of Science:
- Neuroscience
- Visual Neuroscience
- Cortical Processing
Background:
- Neurons in the primary visual cortex (area 17) respond to oriented stimuli within their receptive fields.
- Stimuli outside the receptive field can also modulate neuronal responses, indicating spatial interactions.
Purpose of the Study:
- To investigate the spatial interaction between suprathreshold center and subthreshold surround in area 17.
- To understand how contrast affects these surround interactions and their role in visual perception.
Main Methods:
- Optical imaging of intrinsic signals in area 17 to visualize cortical activity.
- Mapping receptive fields of single neurons.
- Presenting stimuli with and without the aggregate suprathreshold receptive field.
Main Results:
- Stimulus borders generated activity in iso-orientation domains, consistent with long-range horizontal connections.
- Intrinsic signals revealed significant subthreshold surround contributions.
- Surround interactions were contrast-dependent, facilitating responses at low center contrast and suppressing at high center contrast.
Conclusions:
- Spatial interactions in area 17, modulated by contrast, play a key role in visual processing.
- These interactions are fundamental to phenomena like perceptual pop-out and filling-in.