Left perirhinal cortex codes for semantic similarity between written words defined from cued word association

Area of Science:

• Neuroscience
• Cognitive Science
• Psycholinguistics

Background:

• Knowledge of concrete entities involves visual and nonvisual attributes distributed across the neocortex.
• The perirhinal cortex is implicated in memory and knowledge retrieval, but its specific role in processing written word semantics is less understood.

Purpose of the Study:

• To investigate the role of the left perirhinal cortex in retrieving explicit knowledge from written words.
• To determine if this retrieval extends across visual and nonvisual properties, and animate and inanimate entities.
• To compare the left perirhinal cortex's function with surrounding brain regions and with picture-based input.

Main Methods:

• Event-related functional magnetic resonance imaging (fMRI) was used with 18 participants.
• Participants verified properties of concrete entities presented as written words.
• Semantic similarity between stimuli was modeled using word associations.

Main Results:

• The left perirhinal cortex showed a semantic similarity effect for written words, irrespective of property type or entity animacy.
• A similar effect was observed in the left parahippocampal gyrus, but not the hippocampus or right perirhinal cortex.
• Visual and nonvisual property verification engaged distinct cortical networks, with association strength correlating differently with activity in visual and frontal regions.

Conclusions:

• Input modality (written word vs. picture) significantly influences semantic similarity effects in the left perirhinal cortex.
• The left perirhinal cortex functions as a crucial connector hub, linking written word input to distributed semantic representations.
• This region's semantic processing is more dependent on the input format than on the specific knowledge content or semantic control demands.