title: Relationship between transcranial magnetic stimulation measures of intracortical inhibition and spectroscopy measures of GABA and glutamate+glutamine.
abstract: Transcranial magnetic stimulation (TMS) can provide an index of intracortical excitability/inhibition balance. However, the neurochemical substrate of these measures remains unclear. Pharmacological studies suggest the involvement of GABAA and GABAB receptors in TMS protocols aimed at measuring intracortical inhibition, but this link remains inferential. Proton magnetic resonance spectroscopy ((1)H-MRS) permits measurement of GABA and glutamate + glutamine (Glx) concentrations in the human brain and might help in the direct empirical assessment of the relationship between TMS inhibitory measures and neurotransmitter concentrations. In the present study, MRS-derived relative concentrations of GABA and Glx measured in the left M1 of healthy participants were correlated with TMS measures of intracortical inhibition. Glx levels were found to correlate positively with TMS-induced silent period duration, whereas no correlation was found between GABA concentration and TMS measures. The present data demonstrate that specific TMS measures of intracortical inhibition are linked to shifts in cortical Glx, rather than GABA neurotransmitter levels. Glutamate might specifically interact with GABAB receptors, where higher MRS-derived Glx concentrations seem to be linked to higher levels of receptor activity.
authors.affiliation: Centre de recherche en neuropsychologie et cognition, Université de Montréal, Montreal, Quebec, Canada.
authors.forename: Sara
authors.initials: S
authors.lastname: Tremblay
authors.forename: Vincent
authors.initials: V
authors.lastname: Beaulé
authors.forename: Sébastien
authors.initials: S
authors.lastname: Proulx
authors.forename: Louis
authors.initials: L
authors.lastname: de Beaumont
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Marjanska
authors.forename: Julien
authors.initials: J
authors.lastname: Doyon
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
authors.forename: Maryse
authors.initials: M
authors.lastname: Lassonde
authors.forename: Hugo
authors.initials: H
authors.lastname: Théoret
mesh_terms: D000328:Adult; D005260:Female; D018698:Glutamic Acid / Q000032:analysis*; D005973:Glutamine / Q000032:analysis*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009044:Motor Cortex / Q000737:chemistry / Q000502:physiology*; D009433:Neural Inhibition; D050781:Transcranial Magnetic Stimulation; D005680:gamma-Aminobutyric Acid / Q000032:analysis*
chemical_list: D005973:Glutamine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid