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Joseph Viviano, Kevin DeSimone, Keith Schneider; Intrinsic functional connectivity of the humans lateral geniculate nucleus. Journal of Vision 2012;12(9):382. doi: https://doi.org/10.1167/12.9.382.
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Introduction: The lateral geniculate nucleus (LGN) is the thalamic relay between the retina and visual cortex. We sought to measure the functional connectivity between the LGN and other nearby thalamic structures, notably the thalamic reticular nucleus (TRN). The TRN receives excitatory glutamatergic input from the LGN and visual cortices and sends inhibitory GABAergic projections back to the LGN. TRN output generates spindle oscillations in the LGN, disrupting output to V1. This inhibitory complex has been observed in many animal models, but has not yet been observed in the human thalamus. Methods: The present experiment sought to observe functional connectivity in resting humans using functional magnetic resonance imaging (fMRI). Participants were scanned using a Siemens Trio 3T MRI scanner and 32-channel head coil in York University's Neuroimaging Laboratory. Anatomical regions of interest (ROIs) were generated for the LGN and TRN by manually tracing 1 hour of interpolated proton density weighted images. fMRI scans utilized an EPI sequence with a 3 coronal slices, 2mm thick, with a 128 matrix and 192 mm field of view resulting in an in-plane resolution of 1.5 x 1.5 mm2, TR = 0.251, TE = 36 ms, and flip angle of 10°. Four scans of 1200 time points each were collected in which participants were instructed to lie in the scanner with their eyes closed. The anatomically-defined ROIs were coregistered with the EPI data, and the mean time series extracted from the defined LGN mask was correlated with the entire dataset using to find functionally related voxels. Results: We observed significant correlations with the LGN and vascular structures, but not between the left and right LGN, nor with the neighboring thalamic structures. Based on these negative findings we outline multiple future strategies to examine the functional connectivity of the human LGN.
Meeting abstract presented at VSS 2012
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