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Abstract #0140

Endogenous GABA Concentration and Haemodynamic Responses to Graded Visual Contrast

Mark Mikkelsen 1 , C. John Evans 1 , Alan J. Stone 1,2 , Esther A. H. Warnert 1 , and Krish D. Singh 1

1 CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom, 2 FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom

Concentration of the neurotransmitter γ-aminobutyric acid (GABA) is known to predict task-related BOLD and CBF responses. Here, we simultaneously measured BOLD and CBF in the visual cortex whilst employing a graded visual contrast paradigm to investigate GABAs potential association with properties of haemodynamic contrast tuning. GABA levels were non-invasively measured with 1H MRS. Rate of response saturation was inversely related to GABA concentration such that participants with higher GABA levels had faster BOLD response saturation to contrast. GABA concentration is associated with individual differences in haemodynamic contrast tuning and may be a mediator of the dynamic range of BOLD/CBF responses.

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