Biology subjects

Gialopsou, A.

Publications and source records attributed to Gialopsou, A..

4 recordsLinked to original sources

bioRxiv2026

Exploring the beta burst dynamics of cued voluntary movements in Tourette Syndrome

Tourette Syndrome (TS) is a neurodevelopmental hyperkinetic disorder characterised by involuntary tics. These tics are thought to arise due to hyperexcitability of the motor cortex due to disinhibition within the cortico-striato-thalamo-cortical pathway. Given the involvement of motor circuits in this disorder, we explored whether there is a difference in the oscillatory dynamics of voluntary movements in people with tic disorders. We recorded optically pumped magnetometer magnetoencephalography during cued voluntary finger abductions in individuals with tic disorders and age- and sex-matched neurotypical controls. We analysed the data both using conventional time frequency analysis and using hidden Markov modelling to explore the difference in beta burst characteristics and dynamics. Whilst no differences were seen between groups during conventional analysis, we demonstrated an increase in beta burst duration during the post-movement beta rebound within the contralateral motor cortex in individuals with TS suggestive of increased inhibition following movement. We also show evidence of increased contralateral sensorimotor functional connectivity and reduced connectivity from and between frontal regions, as measured using coincident beta bursts. This is suggestive of disrupted functional connectivity within frontal control networks in individuals with TS.

neuroscience↗

bioRxiv2025

Disrupting action control with transcranial ultrasound neuromodulation: a step forward for Tourette syndrome

BackgroundWhile Tourette syndrome (TS) is characterised by the presence of tics, premonitory urges are involved in both triggering them and as a lever to control them. The right insular cortex is known to play a key role in these processes, yet its precise functional contribution remains unclear. Transcranial ultrasound stimulation (TUS) is currently one of the only non-invasive neuromodulation techniques capable of safely and precisely modulating the activity of deep brain structures such as the insula. ObjectiveThis study used TUS to causally investigate the respective roles of the anterior and posterior insula in urge and action control during a blink suppression task. MethodsTwenty healthy adults underwent three TUS sessions targeting the right anterior insula, posterior insula, and posterior ventricle (control site) in a within-subject, crossover design. Behavioural outcomes included blink counts and urge ratings. Additionally, voxel-based correlations were conducted to further estimate the role of each reached area with acoustic stimulation, allowing for a better mechanical understanding. ResultsTUS of the anterior insula induced a clear and acute increase in blink frequency without altering urge, reinforced by voxel-based analyses, confirming its role in voluntary action control. Posterior insula stimulation induced delayed increases in both blinks and urge, which are essentially explained by an involuntary stimulation of the right inferior frontal gyrus. Ventricular stimulation unexpectedly reduced blink frequency during the stimulation only, correlated with acoustic energy delivered within the posterior internal capsule. No significant side effects or temperature rises were observed. ConclusionsThese findings provide the first causal evidence that TUS can modulate the two main features of TS: premonitory urge and action control. Distinct effects across targets highlight the anterior insulas critical role in action control and suggest the internal capsule as a potential therapeutic target for TS.

neuroscience↗

bioRxiv2024

An investigation of the effects of α and β-frequency neural entrainment using tACS on phase-aligned TMS-evoked corticospinal excitability

Deep brain stimulation [DBS] is an effective treatment for many brain disorders (e.g., Parkinsons disease), has a favourable adverse effect profile, and can be particularly effective for individuals with treatment resistant symptoms. DBS is, however, inaccessible for most individuals, is extremely expensive, and is not considered suitable for children and adolescents. For these reasons, non-invasive alternatives to DBS, such as transcranial magnetic stimulation [TMS], are increasingly being sought to treat brain health conditions. Unfortunately, current TMS approaches exhibit large intra- and inter-subject variability in their efficacy, which limits their use clinically. One likely reason for this is that TMS is invariably delivered without reference to ongoing brain activity (i.e., open loop). We propose that the efficacy of stimulation might be improved, and the variability of its effects reduced, if stimulation could be synchronised with ongoing brain activity. To investigate this, we used transcranial alternating current stimulation (tACS) to induce entrainment of brain activity at two frequencies (=10 Hz and {beta}=20 Hz), and we delivered single pulse TMS that was temporally aligned with the phase of each tACS oscillation. To investigate the effects of tACS-phase-aligned TMS we measured motor-evoked potentials (MEPs). Our findings confirm that for -tACS and {beta}-tACS both corticospinal excitability and inter-trial variability varied as a function of tACS phase. Importantly, however, the tACS phase angle that produced maximum TMS-evoked excitability was different for -tACS and {beta}-tACS; coinciding with the negative peak (trough) for -tACS and the positive peak (peak) for {beta}-tACS. These findings confirm that aligning non-invasive brain stimulation to ongoing brain activity may increase the efficacy of TMS and reduce the variability of its effects. However, our results illustrate that the optimal phase of the tACS cycle at which to deliver TMS may vary for different tACS frequencies.

neuroscience↗

bioRxiv2021

Improved spatio-temporal measurements of visually evoked fields using optically-pumped magnetometers

Recent developments in performance and practicality of optically pumped magnetometers have enabled new capabilities in non-invasive brain function mapping through magnetoencephalography. In particular the lack of need of cryogenic operating conditions allows for more flexible placement of the sensor heads closer to the brain surface, leading to improved spatial measurement resolution and increased source localisation capabilities. Through the recording of visually evoked brain fields (VEF), we demonstrate that the closer sensor proximity can be further exploited to improve the temporal resolution. We use optically pumped magnetometers (OPMs), and for reference superconducting quantum interference devices (SQUIDs), to measure brain responses to standard flash and pattern reversal stimuli. We find highly reproducible signals with consistency across multiple healthy participants, stimulus paradigms and sensor modalities. The temporal resolution advantage of OPMs is manifest in a fourfold improvement of the ratio of magnetic signal peak height to temporal width, compared to SQUIDs. The resulting capability of improved spatio-temporal signal tracing is illustrated by simultaneous vector recordings of VEFs in the primary (V1) and associative (V2) visual cortex, where a time lag on the order of 10-20 ms is consistently found. This paves the way for further studies of spatio-temporal neurophysiological signal tracking in visual stimulus processing and other brain responses with potentially far-reaching consequences for time-critical mapping of functionality in the healthy and pathological brains.

neuroscience↗