Visuomotor-coupled otDCS is a promising approach to enhance visual detection, particularly in the peripheral visual field, and is associated with significantly higher visual detection performance, compared to sham, tDCS, and tRNS.
Abstract
Non-invasive brain stimulation (NIBS) allows to investigate the causal relationship between the activity of a target brain region and the performance in a specific task. Regarding visual perception tasks and NIBS of the visual cortex, previous attempts reported mixed results, possibly because of (1) the use of different NIBS protocols, and (2) the lacking consideration that visual perception can be modulated by visuomotor activity. It is therefore still unclear whether the combination of visuomotor activity with which specific NIBS protocol can best influence visual perception. To fill this gap, we measured visual performance (detection) before and after three visuomotor-coupled, excitatory, high-definition NIBS [transcranial direct current stimulation (tDCS), oscilatory tDCS (otDCS), transcranial random noise stimulation (tRNS)] and a sham condition, all delivered to the visual cortex in the human brain. Eighty-four neurotypical participants divided in four groups (tDCS, otDCS, tRNS, Sham) took part in the study. The online visuomotor activity was a virtual reality game where participants had to hit different targets (mosquitoes), repeated for four days. Detection accuracy of visual stimuli was measured on each day. Results showed that otDCS was associated with significantly higher visual detection performance, compared to sham, tDCS, and tRNS, with effects emerging after the first session and becoming more pronounced across subsequent sessions. These effects depended on stimulus eccentricity, with the largest effects observed in the peripheral visual field. These findings suggest that visuomotor-coupled otDCS is a promising approach to enhance visual detection, particularly in the peripheral visual field.
BACKGROUND
Visuomotor integration coordinates visual and motor cortical activity to produce goal-directed responses and can be indexed by Rolandic Mu-rhythm suppression and visual evoked potential (VEP) P100 parameters. Perceptual-motor training improves visuomotor performance, and transcranial direct current stimulation (tDCS) over primary motor cortex (M1) has been reported to enhance motor learning when paired with training. This study examined whether anodal M1 tDCS augments the effects of Senaptec visuomotor training in healthy adults.
METHODS
Sixty participants were randomized to active anodal tDCS (five 10-minute sessions, 1 mA; n = 31) or sham (n = 29) over M1 immediately before each Senaptec training session; 53 completed all sessions and post-testing. Outcomes were Mu-suppression ratios, VEP P100 latency and amplitude, and Senaptec measures of visual sensitivity and visuomotor control.
RESULTS
Active tDCS produced no augmentation of any outcome, with no significant group × time interaction for any measure, consistent across composite and task-level analyses. Training alone produced no change in Mu suppression or visuomotor control. By contrast, both groups showed significant training-related gains in visual sensitivity, including near-far quickness and stereopsis, accompanied by shorter P100 latencies and larger amplitudes, indicating more efficient early visual processing.
CONCLUSIONS
A clear dissociation emerged: training produced robust improvements in early visual processing, whereas neither tDCS nor training altered sensorimotor (Mu) or visuomotor-control measures. The tDCS results should be interpreted cautiously given the modest dose and limited power to detect small effects, rather than as evidence of inefficacy. Tablet-based perceptual training enhanced visual processing independent of neuromodulation.
Jessica Van Bree, Dmitri Poltavski· Neuroscience· 0 citations
Transcranial direct current stimulation (tDCS) on the prefrontal and posterior parietal cortex can enhance mental rotation (MR) performance, whereas little is known about cerebellar tDCS (ctDCS). This study aimed to evaluate effects of ctDCS on a MR task. Fifty-five healthy subjects were randomly assigned to active-ctDCS (1.5 mA; 20 min; n = 28) or sham-ctDCS (n = 27). Participants performed a MR task before (T0) and after (T1) stimulation. In each trial, two shapes appeared on a computer screen, one randomly rotated by 0, 45, 90, or 135 degrees. Subjects pressed the A or L key to indicate whether the shapes were identical or mirrored. A linear mixed model was run on the reaction times (RTs) recorded in each trial. Percent change in RTs (%RT) from T0 to T1 was also computed and analyzed using a second mixed-effects model with planned contrasts. A significant main effect of Time revealed RTs decreased from T0 (M = 3079.35, SE = 102.27) to T1 (M = 2565.36, SE = 102.27). No significant main effects or interactions involving Group were observed in either RT or %RT models. Planned contrasts revealed a single significant difference between groups in the 0° same condition, with the ctDCS group showing a greater reduction in %RT compared to the sham group. No other significant effects were found. ctDCS did not produce a global improvement in MR but showed selective effects under minimal spatial transformation demands. Further studies with different stimulation protocols are needed to clarify its role.
Angelica De Sandi, F. Ruggiero, Denise Mellace et al.· Cognitive Processing· 0 citations
Delay eyeblink conditioning is widely used to study cerebellar function and has been considered a biomarker of cerebellar dysfunction in neurological and psychiatric disorders. A major challenge for repeated testing is transfer of learning across sessions. We tested whether using conditioned stimuli (CSs) from different modalities reduces transfer in humans, whether participants can be stratified into Fast and Slow learners, and whether pupillometry-based blink detection can serve as an alternative to electromyography (EMG). In Experiment 1 (N = 32), participants completed a short screening and two task sessions with auditory and visual CSs paired with an air puff as unconditioned stimulus, followed by extinction training. Learning occurred in both sessions with no difference in overall conditioned response incidences (CRIs) between sessions. However, auditory CSs led to stronger conditioning than visual CSs. In Experiment 2 (N = 16), no screening session was performed, and both task sessions used visual CSs. Here, specific transfer was evident, with high CRIs from the first block of session 2 and a significant session effect. Similarly, transfer occurred from screening to task sessions in Experiment 1 when CSs matched in modality. Across experiments, participants could be stratified into Fast and Slow learners based on median CRIs in the second acquisition training block during screening (Experiment 1) or first task (Experiment 2) sessions. CRIs derived from EMG and pupillometry were highly correlated, confirming pupillometry-based blink detection as a valid MRI-compatible alternative. In sum, transfer is substantial with same-modality CSs, whereas cross-modal designs reduce transfer and enable repeated testing.
Milan Rieger, T. Ernst, D. Timmann et al.· Brain Research· 0 citations
A scoping, narrative roadmap of SSVEP applications organized into three primary domains is provided, highlighting the versatility of SSVEPs in investigating neural mechanisms, supporting diagnosis and treatment of neurological and psychiatric conditions, and advancing brain-computer interface technology.
T. Tsoneva, P. Desain, G. G. Molina et al.· NeuroImage· 0 citations
Responses in the sensory thalamic nuclei are modulated by perceptual tasks. Whether such response modulations rely on feedback from cerebral cortex in humans is unknown. Here, we addressed this question in the context of visual speech recognition: the visual sensory thalamus, i.e. the lateral geniculate nucleus (LGN), has differential BOLD-responses to visual speech than non-speech control tasks. We tested whether such response modulation relies on the function of the visual association cortex, specifically visual-motion area V5/MT. We applied inhibitory transcranial magnetic stimulation (TMS) over bilateral visual-motion sensitive areas V5/MT on 26 healthy adults. Subsequently, participants performed a visual speech and a colour recognition task on identical muted videos of speaking faces during functional magnetic resonance imaging (fMRI). The LGN showed a significant signal change between the visual speech task and the colour task following Vertex stimulation as active control region. This modulation was significantly reduced following inhibitory V5/MT stimulation. V5/MT stimulation also reduced task-dependent functional connectivity between V5/MT and the LGN. These results identify corticothalamic feedback as integral mechanism in visual processing. In particular, the visual association cortex has a causal role in modulating LGN responses during speech recognition.
L. Jeschke, Christa Mueller-Axt, A. Tabas et al.· 0 citations
Understanding how visual information gains access to conscious awareness is a central issue in cognitive neuroscience. Continuous Flash Suppression (CFS) provides a powerful method to investigate this transition by reliably suppressing visual stimuli from awareness. Previous work by Zhu, Drewes, and Melcher (2016) showed that mask frequency influences suppression strength of 2D stimuli, with a peak at 6 Hz. However, whether these findings generalize to more ecologically valid 3D stimuli, and whether CFS strength depends on the eye viewing the stimulus, remains unknown. In this study, we presented a real 3D black disc to one eye, and the dynamic colorful mask to the other one, alternating the eye-of-presentation across blocks. In each trial, the mask flickered at one of ten frequencies ranging from 0 Hz (static) to 32 Hz. Participants responded by pressing a bar as soon as any part of the stimulus became visible. Reaction times (RTs) showed a clear dependence on mask frequency, with maximal suppression occurring at about 6 Hz, as previously found with 2D stimuli, and without reliable differences between right- and left-eye presentations. However, unexpectedly, RTs exhibited a robust bimodal distribution, possibly suggesting specific cognitive processing of 3D stimuli that deserve further investigation. Together, these findings support the view that CFS engages fundamental temporal mechanisms of visual awareness that are shared by both 2D and 3D stimuli and operate at a relatively early, binocular stage of visual processing.
Simona Noviello, A. Toraldo, Mirko Tommasini et al.· Consciousness and Cognition· 0 citations