title: Long-term reproducibility of GABA magnetic resonance spectroscopy.
abstract: Recent findings suggest that cortical gamma aminobutyric acid (GABA) levels may provide a surrogate marker for a number of psychiatric and neurological conditions, as well as behavioural traits. However, the natural variability of GABA levels in the human brain over long periods of time (>8 days) has not yet been studied. The purpose of this work was to investigate the long-term variability of GABA concentrations in the human occipital cortex. Nineteen healthy male participants were recruited and underwent two sessions of magnetic resonance spectroscopy (MRS) to determine occipital GABA levels with an average between-session interval of 7 months. We assessed between-session variability, as well as the correlation between session 1 and session 2 GABA measurements. The mean coefficient of variation between sessions was 4.3% (bootstrap 95% confidence interval: 2.5, 6.4), which is comparable to reported GABA variability measurements over much shorter time intervals (<8 days). A significant positive correlation was observed between session 1 and session 2 GABA measurements (r=0.53, p=0.014), and the intra-class correlation coefficient was calculated to be 0.52 which was also statistically significant (p=0.012). These findings establish experimentally that GABA concentrations in the occipital cortex, as measured by MRS, are relatively stable over periods as long as 7 months. The findings have significant implications for the internal validity of longitudinal studies of GABA levels in the human brain, and they lend foundational support to studies relating GABA levels to behavioural traits in healthy individuals.
authors.affiliation: Douglas Mental Health University Institute and Department of Psychiatry, McGill University, 6875 LaSalle Blvd, Montreal H4H 1R3, Canada; Department of Biomedical Engineering, McGill University, Room 316, Duff Medical Building, 3775 Rue University, Montreal H3A 2B4, Canada. Electronic address: jamie.near@mcgill.ca.
authors.forename: Jamie
authors.initials: J
authors.lastname: Near
authors.affiliation: Center of Functionally Integrative Neuroscience (CFIN), Aarhus University, Nørrebrogade 44, Building 10G, 5th Floor, 8000 Aarhus C, Denmark.
authors.forename: Yi-Ching Lynn
authors.initials: YC
authors.lastname: Ho
authors.affiliation: Cognitive Neurosciences Research Unit (CNRU), Hammel Neurorehabilitation Centre and University Research Clinic, Aarhus University, Nørrebrogade 44, Building 10G, 8000 Aarhus C, Denmark; UCL Institute of Cognitive Neuroscience, University College London, Alexandra House, 17 Queen Square, London WC1N 3AR, UK.
authors.forename: Kristian
authors.initials: K
authors.lastname: Sandberg
authors.affiliation: Department of Biomedical Engineering, McGill University, Room 316, Duff Medical Building, 3775 Rue University, Montreal H3A 2B4, Canada.
authors.forename: Chathura
authors.initials: C
authors.lastname: Kumaragamage
authors.affiliation: Center of Functionally Integrative Neuroscience (CFIN), Aarhus University, Nørrebrogade 44, Building 10G, 5th Floor, 8000 Aarhus C, Denmark; Hammel Neurorehabilitation and Research Centre, Aarhus University Hospital, Voldbyvej 15, 8450 Hammel, Denmark.
authors.forename: Jakob Udby
authors.initials: JU
authors.lastname: Blicher
mesh_terms: D000328:Adult; D001923:Brain Chemistry; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009778:Occipital Lobe / Q000737:chemistry; D015203:Reproducibility of Results; D055815:Young Adult; D005680:gamma-Aminobutyric Acid / Q000032:analysis*
chemical_list: D005680:gamma-Aminobutyric Acid
keywords: Brain; Gamma aminobutyric acid (GABA); Long-term reproducibility; Magnetic resonance spectroscopy (MRS); Neurotransmitter