Role of the left inferior frontal gyrus in covert word retrieval: Neural correlates of switching during verbal fluency
Section snippets
Participants
Ten paid subjects participated (three males and seven females), mean age 22.8 years. All participants were right-handed, native English speakers (i.e., did not learn another language before age 6 years). Participants were also screened for neurological and neuropsychological illnesses, use of psychoactive medications and learning differences (e.g., dyslexia). Participation consisted of a 1 h session. Participants gave informed consent and were compensated with US$ 20.
Materials
A total of 40 category names
Participants
Nine paid subjects participated (four males and five females), mean age 23.1 years; none of these subjects were in Experiment 1. All participants were right-handed, native English speakers (did not learn another language before age 6 years). Participants were also screened for neurological and neuropsychological illnesses, use of psychoactive medications and learning differences (e.g., dyslexia). Participation consisted of a 1 h session. Participants gave informed consent and were compensated
General discussion
The present findings from Experiments 1 and 2 are consistent with the hypothesis that the LIFG subserves processes that support switching between sub-categories during semantic verbal fluency. Notably, in the group random effects analysis, pars triangularis (BA 45) was more highly activated during switching tasks than free generation (Experiment 1) and self-reported clustering (Experiment 2). Activation in BA 45 has been implicated in tasks where verbal responses to stimuli activate many
Summary
Numerous studies have shown ventrolateral PFC involvement during a variety of verbal (Jonides et al., 1998, Kan et al., 2005; Thompson-Schill et al., 2002, Thompson-Schill et al., 1998) and non-verbal tasks (Brandon, Hirshorn, Jha, Fabian, & Thompson-Schill, 2004) where performance requires overriding a highly activated representation or selecting among weakly activated, incompatible representations. We propose that switching during verbal fluency is another instance of a response that depends
Acknowledgements
This research was supported by NIH RO167008 and the Searle Scholars Program. A preliminary version of this study was reported at the annual Human Brain Mapping meeting in 2004. We would like to thank Geoffrey K. Aguirre, Julia C. Lemos and J. Stephen Higgins for their help in the design and analysis of this study. Correspondence regarding this manuscript should be addressed to Sharon L. Thompson-Schill, Department of Psychology, University of Pennsylvania, 3720 Walnut Street B-51, 19104.
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