SHORT-TERM PLASTICITY MEDIATED BY THALAMO-CORTICAL CONNECTIVITY: ULTRA-HIGH FIELD FMRI IN ADULT HUMANS

The potential for long-term plasticity in the sensory brain declines with age, possibly through active stabilization of the sensory circuitry. Nevertheless, adult sensory systems retain the potential for short-term plastic changes: blocking vision in one eye for a few hours in human adults induces a transient boost of the deprived eye. Here we aim to understand the role of the thalamus in gating this plasticity effect.
We used 7TfMRI to assess anatomical, functional and effective connectivity in 22 normally sighted adults, before and after two hours of monocular deprivation. Connectivity was assessed in two conditions: in resting-state (eyes-closed) and during monocular stimulation. Analyses focused on connectivity between V1 and two thalamic nuclei: the lateral geniculate nucleus (LGN) (the main feed-forward input to V1) and the pulvinar (forming cortico-cortical feed-back loops).
Deprivation reduced the resting-state functional connectivity between V1 and the pulvinar (but not their anatomical connectivity). Dynamic Causal Modeling (DCM) indicated a selective decrease of the pulvinar-to-V1 influence, with the opposite direction unaffected. During visual stimulation, the pulvinar-to-V1 connectivity decreased for the deprived eye and increased for the non-deprived eye. Despite its anatomical proximity to the pulvinar, LGN showed a different connectivity pattern, which was unaffected by deprivation during resting and modulated in the opposite direction during visual stimulation. These results are consistent with a model where feed-back signals from the pulvinar inhibit visually driven activity in V1.
Our observations sugggest a revised model of adult V1 plasticity, where short-term reorganization is gated by modulatory signals relayed by the pulvinar.