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Updated: Jul 4, 2026
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Methods to Explore the Influence of Top-down Visual Processes on Motor Behavior
Published on: April 16, 2014
The perceptual and functional consequences of parietal top-down modulation on the visual cortex
Juha Silvanto1, Neil Muggleton, Nilli Lavie
1Institute of Cognitive Neuroscience and Department of Experimental Psychology, University College London, Alexandra House, 17 Queen Square, London, UK. jsilvant@bidmc.harvard.edu
Cerebral Cortex (New York, N.Y. : 1991)
|June 3, 2008
Summary
The posterior parietal cortex (PPC) influences visual cortex activity, increasing excitability when stimulated unilaterally. Bilateral stimulation abolished this effect, revealing interhemispheric competition in visual modulation.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Visual Neuroscience
Background:
- The posterior parietal cortex (PPC) is hypothesized to mediate top-down control over visual processing in occipital areas.
- Understanding the PPC's role in visual modulation is crucial for comprehending visual attention and perception.
Purpose of the Study:
- To investigate the functional role of the PPC in modulating visual cortex activity.
- To examine the influence of unilateral versus bilateral PPC stimulation on visual cortical excitability.
Main Methods:
- Utilized transcranial magnetic stimulation (TMS) to induce activity in the PPC (angular gyrus).
- Measured visual cortical excitability using the phosphene threshold in visual areas V1/V2.
- Compared effects of unilateral and bilateral PPC TMS application.
Main Results:
- Unilateral TMS over the PPC reduced the stimulation intensity needed to elicit phosphenes, indicating increased visual cortical excitability.
- Bilateral TMS over the PPC abolished the observed increase in visual cortical excitability.
- Demonstrated top-down modulation from the PPC to the visual cortex.
Conclusions:
- The PPC exerts top-down control over visual cortex activity.
- These top-down effects are modulated by interhemispheric interactions between the cerebral hemispheres.
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