TAMIETTO M. - MIUR - PRIN 2017 Linea A - From brain dynamics to restoration of visual awareness after damage to the visual cortex

Visual awareness - the online access to the content of our visual experience - affords flexibility and experiential richness, and its loss following brain damage has devastating effects. However, patients with blindness following damage to the visual cortex (V1) may retain non-conscious visual functions, despite visual awareness is lacking. The overarching goal of the present project is to translate these nonconscious visual abilities into conscious one. This requires moving the research agenda from the current study of the neural correlates of visual awareness to the neural causes determining it. To achieve this translational objective, we propose to integrate into a coherent framework three main properties of visual processing: topological, dynamic and oscillatory characteristics. In doing so, we will place our understanding of visual awareness on firm neuropsychological and empirical bases. Next, we will translate this wisdom into evidence-based clinical intervention. Topologically, the areas composing the visual system have been broadly organised into two distinct processing pathways: a ventral pathway for object recognition, that leads to visual awareness, and a dorsal pathway for action that does not evoke a conscious percept. This dichotomy is under renewed scrutiny and we will explore the possibility that other organization principles apply. For example, important structures for perception at the fringes of visual periphery, such as area prostriate, do not fit in this dichotomy. This part of the project integrates non-invasive MRI methods that analyse in vivo connectional and structural properties, such as tractography and myelin maps (UniTO team), event-related optical signal (EROS) applications (UniVR team) and transcranial magnetic stimulation (TMS) to induce conscious visual percepts by stimulating specific nodes of the visual network, while simultaneously recording neural dynamics with EROS (UniVR). The outcome will be that of clarifying the structural, functional and connectional properties of different components of the visual system in the healthy human brain, and how the V1 lesion alters these functions and connections. Dynamically, the temporal properties of inter-regional interactions are often considered to be crucial for awareness to emerge, as for example re-entrant feedback from higher-level temporal areas to V1. In this section, we will test these dynamic interactions at the high temporal (< 10 ms) and spatial resolution (< 0.5 cm) achievable with near-infrared spectroscopy (NIRS), which samples online neural activity of brain networks specifically linked to awareness during task execution (UniVR). We complement this task-dependent approach with task-free fMRI paradigms applying dynamic functional connectivity; an innovative method that analyses spontaneous shifts of inter-regional connectivity related to awareness at 50 sec epochs temporal resolution (UniTO). The result will be to build up a quantitative and refutable model that specifies the path of information flow across nodes in the visual system and their causal role in generating visual awareness. Thirdly, spontaneous oscillations of brain rhythm have been traditionally used as biomarkers of different levels of consciousness, such as wakefulness or coma, but seldom applied in relation to visual awareness in alert subjects. Moreover, there is converging evidence that oscillations in the range of alpha band (7-13 Hz) are directly related to activity in the visual system. Preliminary findings from UniBO show a reduction of the alpha power and alpha frequency peak specific for the hemisphere with V1 damage. We will therefore explore for the first time how the impaired indices in the alpha range of patients with damage to V1 are related to their visual performance. The last part of the project will devise rehabilitative protocols to promote the (re)emergence of lost visual awareness following V1 damage, thereby exploiting the clinical potenti