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. 2022 Jan 18;119(4):e2113313119. doi: 10.1073/pnas.2113313119

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Copyright © 2022 the Author(s). Published by PNAS.

This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY).

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Fig. 3. — Dissection of somatosensory-driven thalamic fMRI responses with cortical silencing. (A) Schematic diagrams to determine the contribution of long-range inputs to somatosensory-evoked thalamic fMRI responses by means of optogenetic cortical inhibition. Functional activities in thalamic nuclei during FP stimulation can originate from multiple long-range inputs via ST and CT pathways, whereas differences in thalamic fMRI responses (Diff with a subscript indicating the inactivation site) between optogenetic cortical inactivation with and without sensory stimulation are related to all possible inputs except those from the target cortex of the S1FL, M1, and S2 to the thalamic nuclei; thus, with comparison of those conditions (Diff versus FP), the contribution of each pathway to thalamic responses was investigated. (B) fMRI maps of the thalamic nuclei. FP stimulation induced activity in two distinct foci, VPL and POm (FP: n = 22). Somatosensory-evoked activities in the VPL were maintained in the fMRI difference maps (Diff) between optogenetic cortical inactivation with and without FP, whereas POm activity disappeared in the difference map of S1FL inactivation (Diff_S1FL: n = 8) but not M1 (Diff_M1) and S2 (Diff_S2) inactivation (n = 7, each). LD, lateral dorsal nucleus; MD, mediodorsal nucleus; VM, ventral medial nucleus; Int, internal capsule; and ZI, zona incerta. (Scale bar, 0.5 mm.) (C and D) Contribution of functional pathways to somatosensory-evoked VPL and POm responses. fMRI time courses in (C) the VPL and (D) the POm for the difference between combined stimulation and cortical silencing (Diff_S1FL, blue lines; Diff_M1, green lines; and Diff_S2, red lines) and those for FP only (FP, black lines) were compared. (C) Under cortical silencing with and without FP, those differential responses (colored bar) are similar to the total VPL responses (gray bar), (D) whereas the sensory-evoked POm response was completely suppressed during S1FL silencing (blue bar) but not during M1 (green bar) and S2 (red bar) silencing. Therefore, the VPL has dominant inputs from the spinal cord, not the cortex, and POm activity is directly driven by the S1FL, not by the spinal cord. Gray vertical bar in time courses, 20-s stimulus; error bars, SEM; n.s., not significant; and **P < 0.01 (paired t test).