Induction of Semantic Impairments Using rTMS: Evidence for the Hub-And-Spoke Semantic Theory

Abstract

Semantic cognition permits us to bring meaning to our verbal and nonverbal experiences and to generate context and time-appropriate behavior. Parallel studies of semantic dementia, rTMS in normal participants and neuroimaging indicate that the anterior temporal lobe (ATL) plays a crucial and necessary role in conceptualization by merging experience into an amodal semantic representation. In this rTMS investigation, we tested the differential contribution of both regions for the first time. We adjudicated between these competing theories by investigating category specific impairments. Thus stimulation at this site should induce a category specific impairment which, as far as we are aware, has never been demonstrated before in neurologically intact participants. To examine emerging category effects from original 200 items we created two lists of living and nonliving items matched for familiarity, frequency and visual complexity. Each stimulation site produced significantly different effects on the two categories. In summary, through the use of rTMS in normal participants, we have been able to demonstrate two contrasting effects. Stimulation of the ATL leads to a generalized slowing of semantic processing across all types of concept. The findings of this study fit squarely with the hub-and-spoke model of semantic memory and rule out the other models. (PsycINFO Database Record (c) 2017 APA, all rights reserved)