Short-term sensory deprivation impacts the physiology of the visual brain studied with ultra-high field fMRI in adult humans

The nervous system can change, structurally and functionally, in response to experience. This property is called plasticity. It is fundamental in the post-natal period, when neural connections in many brain areas are shaped by our interactions with the environment. In adulthood, plasticity becomes selective; it is still observed in some neural circuits (e.g. those supporting memory) but not in others. For example, sensory systems progressively loose their plasticity, and they are assumed to be stale and hardwired in adults. In contrast with this assumption, a decade of studies demonstrated that the adult visual system retains a form of short-term plasticity, compatible with a homeostatic phenomenon and triggered by short-term sensory deprivation. In particular, short-term monocular deprivation (closure of one eye for a few hours) induces a transient boost of the visual cortex response to the deprived eye. Using ultra-high field fMRI in human adults, we investigated this phenomenon by asking three key questions: 1. can we replicate the modulation of responses in the primary visual cortex following short-term monocular deprivation (previously reported in [Binda et al., 2018])? 2. is this modulation contrast-dependent, i.e. affected by the strength (contrast) of the visual stimuli? 3. is it supported by a change in the connectivity among visual brain areas? 7T fMRI data were collected before and after 2 hours of monocular deprivation in 25 normally sighted adult humans. During acquisitions, participants were presented with stimuli of variable contrast. Visually evoked responses were estimated for three a priori selected regions of interest. These include the lateral geniculate nucleus and the primary visual cortex, the first two steps in the visual processing cascade. In addition, we analysed the pulvinar, another thalamic nucleus that was previously shown to respond to monocular deprivation [Kurzawski et al., 2022]. Preliminary results suggest that contrast does modulate the effect of sensory deprivation on responses in primary visual cortex. Moreover, the plasticity effect is accompanied by a modulation of connectivity between the three regions of interest. This suggests that short-term sensory deprivation modulates responses at the earliest stages of visual processing, promoting a reorganization of the functional connections between the cortex and the thalamus.