title: Cortical inhibition of distinct mechanisms in the dorsolateral prefrontal cortex is related to working memory performance: a TMS-EEG study.
abstract: Paired-pulse transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) is a method for studying cortical inhibition from the dorsolateral prefrontal cortex (DLPFC). However, little is known about the mechanisms underlying TMS-evoked cortical potentials (TEPs) from this region, let alone inhibition of these components. The aim of this study was to assess cortical inhibition of distinct TEPs and oscillations in the DLPFC using TMS-EEG and to investigate the relationship of these mechanisms to working memory. 30 healthy volunteers received single and paired (interstimulus interval = 100 msec) TMS to the left DLPFC. Variations in long-interval cortical inhibition (LICI) of different TEP peaks (N40, P60, N100) and different TMS-evoked oscillations (alpha, lower beta, upper beta, gamma) were compared between individuals. Variation in N100 slope following single pulse TMS, another putative marker of inhibition, was also compared with LICI of each measure. Finally, these measures were correlated with performance of a working memory task. LICI resulted in significant suppression of all TEP peaks and TMS-evoked oscillations (all p < .05). There were no significant correlations between LICI of different TEP peaks or TMS-evoked oscillations with the exception of P60 and N100. Variation in N100 slope correlated with LICI of N40 and beta oscillations. In addition, LICI of P60 and N100 were differentially correlated with working memory performance. The results suggest that both the LICI paradigm and N100 following single pulse TMS reflect complementary methods for assessing GABAB-mediated cortical inhibition in the DLPFC. Furthermore, these measures demonstrate the importance of prefrontal GABAB-mediated inhibitory control for working memory performance.
authors.affiliation: Monash Alfred Psychiatry Research Centre, Central Clinical School, The Alfred and Monash University, Melbourne, Australia; Monash Clinical and Imaging Neuroscience, School of Psychological Science and Monash Biomedical Imaging, Monash University, Melbourne, Australia. Electronic address: nigel.rogasch@monash.edu.
authors.forename: Nigel C
authors.initials: NC
authors.lastname: Rogasch
authors.affiliation: Temerty Centre for Therapeutic Brain Intervention, Centre for Addiction and Mental Health, University of Toronto, Toronto, Canada.
authors.forename: Zafiris J
authors.initials: ZJ
authors.lastname: Daskalakis
authors.affiliation: Monash Alfred Psychiatry Research Centre, Central Clinical School, The Alfred and Monash University, Melbourne, Australia.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fitzgerald
mesh_terms: D000328:Adult; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D009483:Neuropsychological Tests; D017397:Prefrontal Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Cortical inhibition; Dorsolateral prefrontal cortex; Electroencephalography; Transcranial magnetic stimulation; Working memory