Biology subjects

Ellena, G.

Publications and source records attributed to Ellena, G..

4 recordsLinked to original sources

bioRxiv2025

Hemispheric Dissociation Revealed by Attentional Isolation and tRNS

Prolonged sensory imbalance, induced by directing attention to one visual field, can paradoxically enhance performance in the opposite, non-attended visual field. This effect is likely driven by the brains homeostatic mechanisms that regulate excitation and inhibition between hemispheres in homotopic attention processing regions. Here, we employed transcranial random noise stimulation (tRNS) to modulate cortical excitability and probe its role in interhemispheric dynamics controlling visual attention. Specifically, we used a procedure called attentional isolation, where neurotypical participants covertly focused their visual attention in one hemifield (the attended visual field) for 30 minutes. Performance changes in both the unattended (opposite) visual field and the attended visual field were measured following this manipulation. We applied transcranial random noise stimulation (tRNS) over the right or left frontoparietal cortex to modulate the excitability of one hemisphere relative to the other during attention isolation, probing the neural mechanisms underlying the observed contralateral performance shift. Our results showed improved performance in the previously unattended visual field following the attentional isolation period after sham stimulation. However, tRNS revealed a functional dissociation between the hemispheres: right hemisphere active stimulation abolished the performance improvement, while left hemisphere stimulation preserved it. These findings suggest distinct roles for the left and right hemispheres in modulating paradoxical visual performance shifts and may inform the development of novel neurorehabilitation strategies for clinical populations.

neuroscience↗

bioRxiv2024

Modulation of learning-dependent plasticity in the attention network

Non-invasive brain stimulation, such as transcranial random noise stimulation (tRNS), has been shown to enhance cortical excitability and facilitate perceptual learning. However, the neural mechanisms underlying these effects remain poorly understood. Here, we demonstrate that tRNS over the bilateral intraparietal sulcus (IPS) optimizes learning by preventing the decline in neural activity that occurs during short, high-load attentional training, thereby sustaining excitability and enhancing behavioral performance. Using a multi-session tRNS-fMRI paradigm, we investigated how tRNS modulates learning-related plasticity in the attention network during cognitive training. In the sham condition we observed a significant decline in task-evoked BOLD after the training and no behavioral improvement, suggesting crucial neural changes associated with cognitive training that are not evident in the behavioral data. Conversely, in the active tRNS condition, stimulation not only prevented the early decline in task-evoked BOLD activity observed in the sham condition, but it increased it. This change in BOLD activity correlated with improved performance. This suggests that tRNS counteracts early neural adaptation during short training protocols, sustaining activity in task-relevant cortical regions to enable learning that would otherwise fail. By providing the first direct evidence that tRNS mitigates early neural downregulation and preserves functional response dynamics during learning in crucial task-related cortical areas, our study demonstrates that in parietal cortex training-induced plasticity is not accompanied by efficiency-driven reductions in activation, like typically seen in sensory areas. Instead, we propose that sustaining neural excitability through tRNS prolongs plasticity and optimizes cognitive performance in higher order attentional areas. These findings highlight tRNS as a powerful tool for enhancing attentional learning and modulating neuroplasticity in both healthy and clinical populations.

neuroscience↗

bioRxiv2024

When Attention Hurts: The Effect Of rTMS On Neural Correlates Of Time Perception

The parietal lobe plays a crucial role in the attentional networks that help shape our perception, including our perception of time. Based on neuropsychological and neurophysiological evidence, a "when" pathway including the right parietal lobe has been proposed as the critical cortical site for the discrimination of objects across time. When an oddball stimulus is presented in a stream of identical standard stimuli, it is perceived as lasting longer, even when its actual duration is shorter. While attentional capture seems to play a major role in this subjective expansion of time the cortical mechanisms responsible for this effect remain unclear. We therefore set to investigate the direct role of parietal brain areas in time perception using combined repetitive transcranial magnetic stimulation (rTMS) and electroencephalogram (EEG). We measured the perceived duration of an oddball stimulus in each participant before and after inhibitory 1-Hz rTMS stimulation at one of three scalp locations: the right intraparietal sulcus (rIPS), the right inferior parietal lobe (rIPL), or the occipital cortex as a control. EEG was recorded throughout. Stimulation over the rIPL caused a more veridical experience of times subjective expansion towards the oddball, while rTMS over the rIPS and the occipital cortex had no effect. These data provide theoretically challenging notions to the concept of the cortexes role within time perception and the mechanisms involved.

neuroscience↗

bioRxiv2021

Acute stress affects peripersonal space representation

Peripersonal space (PPS) is the region of space surrounding the body. It has a dedicated multisensory-motor representation, whose purpose is to predict and plan interactions with the environment, and which can vary depending on environmental circumstances. Here, we investigated the effect on the PPS representation of an experimentally induced stress response. We assessed PPS representation in healthy humans, before and after a stressful manipulation, by quantifying visuotactile interactions as a function of the distance from the body, while monitoring salivary cortisol concentration. Participants, who showed a cortisol stress response, presented enhanced visuotactile integration for stimuli close to the body and reduced for far stimuli. Conversely, individuals, with a less pronounced cortisol response, showed a reduced difference in visuotactile integration between the near and the far space. In our interpretation, physiological stress resulted in a freezing-like response, where multisensory-motor resources are allocated only to the area immediately surrounding the body.

neuroscience↗