Changes in "top-down" connectivity underlie repetition suppression in the ventral visual pathway

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Visual Perception

Background:

• Repetition suppression (RS) is a decrease in neural activity when a stimulus is repeated.
• Functional magnetic resonance imaging (fMRI) studies often observe RS across various object categories.
• Two main hypotheses explain RS: local neural fatigue or top-down modulation between brain regions.

Purpose of the Study:

• To investigate the mechanisms underlying RS in the human visual cortex, specifically within the body-sensitive network.
• To differentiate between local (within-region) and top-down (between-region) explanations of RS.
• To determine if RS mechanisms differ for identical stimuli versus stimuli with changing size or view.

Main Methods:

• Used fMRI to study RS in the extrastriate body area (EBA) and fusiform body area (FBA).
• Presented identical body images and images with varying body size or view.
• Employed dynamic causal modeling (DCM) to analyze effective connectivity between brain regions.

Main Results:

• Both EBA and FBA exhibited RS to identical body images, irrespective of size or view changes.
• Dynamic causal modeling revealed that top-down (FBA-to-EBA) connectivity changes are crucial for RS.
• Repetition of identical images additionally involved forward connectivity changes (EBA-to-FBA).

Conclusions:

• RS is primarily driven by top-down modulation within neural networks.
• The role of feedforward connectivity in RS depends on whether the repeated stimulus is identical or varies.
• Findings challenge existing interpretations of neural representations derived from fMRI RS paradigms.