The neural basis for categorization in semantic memory.
We asked young adults to categorize written object descriptions into one of two categories, based on a rule or on overall similarity, while we monitored regional brain activity with functional magnetic resonance imaging (fMRI). We found significantly greater recruitment of left dorsolateral prefrontal cortex for rule-based categorization in direct comparison with similarity-based categorization. Recruitment of right ventral frontal cortex and thalamus was uniquely associated with rule-based categorization as well. These observations lend support to the claim that executive functions such as working memory, inhibitory control, and selective attention contribute to rule-based categorization. Right inferior parietal activation was uniquely associated with similarity-based categorization. This region may play an important role in overall feature configuration that is important for this form of categorization. We found other brain regions recruited for both rule-based and similarity-based categorization: Anterior cingulate cortex may support the implementation of executive functions during situations with competing response alternatives; and left inferior parietal cortex may be related to the integration of feature knowledge about objects represented in modality-specific association cortices. We also administered a degraded-similarity condition where the task of categorizing a written object description was made more difficult by perceptually degrading the stimulus materials. The degraded condition and the rule-based condition, but not the similarity-based condition, were associated with caudate activation. The caudate may support resource demands that are not specific for a particular categorization process. These findings associate partially distinct large-scale neural networks with different forms of categorization in semantic memory.
Grossman
Murray
M
Department of Neurology, University of Pennsylvania, Philadelphia, 19104, USA. mgrossma@mail.med.upenn.edu
Smith
Edward E
EE
Koenig
Phyllis
P
Glosser
Guila
G
DeVita
Chris
C
Moore
Peachie
P
McMillan
Corey
C
D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D002421:Caudate Nucleus / Q000502:physiology; D002540:Cerebral Cortex / Q000502:physiology*; D003657:Decision Making / Q000502:physiology; D004193:Discrimination Learning / Q000502:physiology*; D005260:Female; D006179:Gyrus Cinguli / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology; D011340:Problem Solving / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012660:Semantics; D014706:Verbal Learning / Q000502:physiology*