Motor Cortex Excitation/Inhibition Imbalance in Young Adults With Autism Spectrum Disorder: A MRS-TMS Approach

Inês Bernardino; Ana Dionísio; Inês R Violante; Raquel Monteiro; Miguel Castelo-Branco

doi:10.3389/fpsyt.2022.860448

Motor Cortex Excitation/Inhibition Imbalance in Young Adults With Autism Spectrum Disorder: A MRS-TMS Approach

Front Psychiatry. 2022 Apr 14:13:860448. doi: 10.3389/fpsyt.2022.860448. eCollection 2022.

Authors

Inês Bernardino^{1

2

3}, Ana Dionísio^{2

3}, Inês R Violante⁴, Raquel Monteiro^{2

3}, Miguel Castelo-Branco^{1

2

3}

Affiliations

¹ Faculty of Medicine, University of Coimbra, Coimbra, Portugal.
² Coimbra Institute for Biomedical Imaging and Translational Research, University of Coimbra, Coimbra, Portugal.
³ Institute of Nuclear Sciences Applied to Health, University of Coimbra, Coimbra, Portugal.
⁴ School of Psychology, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.

Abstract

Excitatory/inhibitory imbalance has been suggested as a neurobiological substrate of the cognitive symptomatology in Autism Spectrum Disorder (ASD). Studies using magnetic resonance spectroscopy (MRS) attempted to characterize GABA and Glutamate brain levels in ASD. However mixed findings have been reported. Here, we characterize both neurochemical and physiological aspects of GABA system in ASD by implementing a more comprehensive approach combining MRS and transcranial magnetic stimulation (TMS). A group of 16 young ASD adults and a group of 17 controls participated in this study. We employed one MRS session to assess motor cortex GABA+ and Glutamate+Glutamine (Glx) levels using MEGAPRESS and PRESS sequences, respectively. Additionally, a TMS experiment was implemented including paired-pulse (SICI, ICF and LICI), input-output curve and cortical silent period to probe cortical excitability. Our results showed a significantly increased Glx, with unchanged GABA+ levels in the ASD group compared with controls. Single TMS measures did not differ between groups, although exploratory within-group analysis showed impaired inhibition in SICI5ms, in ASD. Importantly, we observed a correlation between GABA levels and measures of the input-output TMS recruitment curve (slope and MEP amplitude) in the control group but not in ASD, as further demonstrated by direct between group comparisons. In this exploratory study, we found evidence of increased Glx levels which may contribute to ASD excitatory/inhibitory imbalance while highlighting the relevance of conducting further larger-scale studies to investigate the GABA system from complementary perspectives, using both MRS and TMS techniques.

Keywords: GABA; autism (ASD); glutamate; magnetic resonance spectroscopy; transcranial magnetic stimulation.