Alpha oscillations reveal implicit visual processing of motion in hemianopia. Cortex 122, 81-96.

After lesion or deafferentation of the primary visual cortex, hemianopic patients experience loss of conscious vision in their blind field. However, due to the spared colliculo-extrastriate pathway, they might retain the ability to implicitly process motion stimuli through the activation of spared dorsal-extrastriate areas, despite the absence of awareness. To test this hypothesis, Electroencephalogram (EEG) was recorded from a group of hemianopic patients without blindsight (i.e., who performed at chance in different forced-choice tasks), while motion stimuli, static stimuli or no stimuli (i.e., blank condition) were presented either in their intact or in their blind visual field. EEG analyses were performed in the time-frequency domain. The presentation of both motion and static stimuli in the intact field induced synchronization in the theta band and desynchronization both in the alpha and the beta band. In contrast, for stimuli presented in the blind field, significantly greater desynchronization in the alpha range was observed only after the presentation of motion stimuli, compared to the blank condition, over posterior parietal-occipital electrodes in the lesioned hemisphere, at a late time window (500-800 msec). No alpha desynchronization was elicited by static stimuli. These results show that hemianopic patients can process only visual signals relying on the activation of the dorsal pathway (i.e., motion stimuli) in the absence of awareness and suggest different patterns of electrophysiological activity for conscious and unconscious visual processing. Specifically, visual processing in the absence of awareness elicits an activity limited to the alpha range, most likely reflecting a “local” process, occurring within the extrastriate areas and not participating in inter-areal communication. This also suggests a response specificity in this frequency band for implicit visual processing. In contrast, visual awareness evokes changes in different frequency bands, suggesting a “global” process, accomplished by activity in a wide range of frequencies, probably within and across cortical areas.

Effects of different transcranial direct current stimulation protocols on visuo-spatial contextual learning formation: evidence of homeostatic regulatory mechanisms”. Scientific Reports, 10(1), 1-14.

In the present study we tested the effects of different transcranial direct current stimulation (tDCS) protocols in the formation of visuo-spatial contextual learning (VSCL). The study comprised three experiments designed to evaluate tDCS-induced changes in VSCL measures collected during the execution of a visual search task widely used to examine statistical learning in the visuo-spatial domain. In Experiment 1, we probed for the effects of left-posterior parietal cortex (PPC) anodal-tDCS (AtDCS) at different timings (i.e. offline and online) and intensities (i.e. 3 mA and 1.5 mA). The protocol producing the more robust effect in Experiment 1 was used in Experiment 2 over the right-PPC, while in Experiment 3, cathodal-tDCS (CtDCS) was applied over the left-PPC only at a high intensity (i.e. 3 mA) but varying timing of application (offline and online). Results revealed that high intensity offline AtDCS reduced VSCL regardless of the stimulation side (Experiment 1 and 2), while no significant behavioral changes were produced by both online AtDCS protocols (Experiment 1) and offline/online CtDCS (Experiment 3). The reduced VSCL could result from homeostatic regulatory mechanisms hindering normal task-related neuroplastic phenomena.

“Shaping the visual system: cortical and subcortical plasticity in the intact and the lesioned brain”. Neuropsychologia.

Visual system is endowed with an incredibly complex organization composed of multiple visual pathway affording both hierarchical and parallel processing. Even if most of the visual information is conveyed by the retina to the lateral geniculate nucleus of the thalamus and then to primary visual cortex, a wealth of alternative subcortical pathways is present. This complex organization is experience dependent and retains plastic properties throughout the lifespan enabling the system with a continuous update of its functions in response to variable external needs. Changes can be induced by several factors including learning and experience but can also be promoted by the use non-invasive brain stimulation techniques. Furthermore, besides the astonishing ability of our visual system to spontaneously reorganize after injuries, we now know that the exposure to specific rehabilitative training can produce not only important functional modifications but also long-lasting changes within cortical and subcortical structures. The present review aims to update and address the current state of the art on these topics gathering studies that reported relevant modifications of visual functioning together with plastic changes within cortical and subcortical structures both in the healthy and in the lesioned visual system.