Functional connectivity with cortical depth assessed by resting state fMRI of subregions of S1 in squirrel monkeys

Abstract

Whereas resting state BOLD (blood oxygenation-level dependent) functional MRI (fMRI) has been widely used to assess functional connectivity between cortical regions, the laminar specificity of such measures is poorly understood. This study aims to determine (a) whether the resting state functional connectivity (rsFC) between two functionally related cortical regions varies with depth, (b) the relationship between layer-resolved tactile stimulus-evoked activation pattern and inter-layer rsFC pattern between two functionally distinct but related areas 3b and 1, and (c) the effects of spatial resolution on rsFC measures. We examined the inter-layer rsFC between somatosensory areas 3b and 1 of squirrel monkeys under anesthesia using tactile stimulus-driven and resting state BOLD acquisitions at sub-millimeter resolution. Consistent with previous observations in the areas 3b and 1, we detected robust stimulus-evoked BOLD activations with foci confined mainly to the upper layers (centered at 21% of the cortical depth). By carefully placing seeds in upper, middle and lower layers of areas 3b and 1, we observed strong rsFC between superficial and middle layers of these two areas. The layer-resolved activation patterns in areas 3b and 1 agree with their inter-layer rsFC patterns, and are consistent with the known anatomical connections between layers. In summary, using BOLD rsFC pattern we identified an inter-layer inter-areal microcircuit that shows strong intrinsic functional connections between superficial and middle layer somatosensory areas 3b and 1 of monkeys. RsFC can be used as a robust invasive tool to probe inter-layer cortico-cortical microcircuits.

Cortical depth-dependent human fMRI of resting-state networks using EPIK

“…S6). These findings are in agreement with previous reports demonstrating a higher level of activity and communication near the surface of the cortex in humans and non-human primates during rest [64,65]. Concerned that our results highlighting the role of superficial layers may simply reflect a surface-vein-related bias, we conducted an additional assessment in three separate regions that are presumably engaged in motor processing.…”

Flexible annotation atlas of the mouse brain: combining and dividing brain structures of the Allen Brain Atlas while maintaining anatomical hierarchy

“…Still, node for each cortical layer was 13-25 times larger than a single voxel of fMRI (30 nL), except for layer 6b (77 nL). Significant variation in FC within vs. between supra-granular and infragranular layers was found in most cortical regions, which is apparently consistent with results of earlier studies examining laminar differences of neuronal activity measured using calcium imaging (Ayaz et al, 2019), electrophysiology (Sakata and Harris, 2009), and fMRI (Mishra et al, 2019). It is noteworthy that such layer-specific FC was observed both in the dorsal (e.g.…”

“…Laminar fMRI is an emerging field for deciphering interaction of the brain, discriminating input layers and output layers in the cortex (Goense et al, 2012;Norris and Polimeni, 2019;Scheeringa and Fries, 2017;Yu et al, 2014). Resting-state FC analysis between cortical layers with fMRI is under active investigation with challenges related to spatial resolution of fMRI and vascular distribution in the cortex (Mishra et al, 2019;Poplawsky et al, 2019). In the present study, cortical layer-specific FC analysis was attempted using FAAdetailed, which defined thin but large nodes for cortical layers.…”

Flexible annotation atlas of the mouse brain: combining and dividing brain structures of the Allen Brain Atlas while maintaining anatomical hierarchy

“…Still, node for each cortical layer was 13–25 times larger than a single voxel of fMRI (30 nL), except for layer 6b (77 nL). Significant variation in FC within vs. between supra-granular and infragranular layers was found in most cortical regions, which is apparently consistent with results of earlier studies examining laminar differences of neuronal activity measured using calcium imaging 52 , electrophysiology 53 , and fMRI 50 . It is noteworthy that such layer-specific FC was observed both in the dorsal (e.g.…”

“…Laminar fMRI is an emerging field for deciphering interaction of the brain, discriminating input layers and output layers in the cortex 46 – 49 . Resting-state FC analysis between cortical layers with fMRI is under active investigation with challenges related to spatial resolution of fMRI and vascular distribution in the cortex 50 , 51 . In the present study, cortical layer-specific FC analysis was attempted using FAAdetailed, which defined thin but large nodes for cortical layers.…”