Abstract #0049

Visual contrast levels modulate excitation and inhibition in the human visual cortex – a combined fMRI-MR Spectroscopy study at 7 Tesla

Betina Ip^1,2, Uzay E Emir^1,3, Andrew J Parker², and Holly Bridge¹

¹Wellcome Centre for Integrative Neuroimaging, FMRIB Division, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom, ²Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom, ³College of Health and Human Sciences, Purdue University, West Lafayette, IN, United States

We used 7 Tesla combined fMRI-MRS to show that simultaneously measured hemodynamic and neurochemical responses in the human visual cortex changed as a function of visual contrast. BOLD change increased linearly to rise in visual contrast, glutamate increased and GABA decreased. Quantification of this change using an excitation:inhibition index demonstrated a switch from inhibitory-dominant to excitatory-dominant neurochemical response. Our results are a step towards disambiguating contributions of cortical excitation and inhibition to stimulus evoked hemodynamic response.

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