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Abstract:
A pronounced characteristic of the microcircuits of the primary visual cortex (striate cortex or area V1) in primates is the strong recurrent excitation and the tight balance between excitation and inhibition. The electrically inseparable events can be best studied if electrophysiological experiments are combined with studies tracking the changes in neurotransmitter concentrations during stimulus-induced excitation. Magnetic resonance spectroscopy (MRS) is ideally suited for such physiology-neurochemistry experiments; yet the highly convoluted form of the human V1 has thus far prevented the performance of MRS investigations that are spatially confined within the gray matter of this area. Typically, these studies are compromised by partial volume contaminations originating from white matter tissue, cerebrospinal fluid and other cortical areas. Here, the relative flatness of V1 in macaques was exploited to enable single voxel 1H MRS from a small volume (5x1.6x5 mm3, 40 microL) that was entirely confined within
the V1 gray matter of anesthetized monkeys. Line widths of (13.5±1.9) Hz and (13.0±1.3) Hz for water and creatine respectively were achieved with a two-step shimming-strategy for voxels at the brain surface. The quality of the obtained results paves the way for further neuroscientific research, including studies of the cortical microcircuits and the dynamic longitudinal changes occurring during cortical reorganization and plasticity.