Biology subjects

Vesia, M.

Publications and source records attributed to Vesia, M..

7 recordsLinked to original sources

bioRxiv2026

Frontal stimulation reshapes SCAN connectivity and improves motor function in Parkinson's disease

Parkinson's disease is a neurodegenerative disorder with characteristic motor deficits of bradykinesia and impaired coordination, and non-motor deficits affecting cognitive abilities such as attention and executive functions. Recent evidence suggests that some canonical motor deficits in Parkinson's disease (e.g., freezing of gait) are associated with abnormalities in frontal cortical processing typically thought to underlie executive functions such as cognitive control. The evidence from human research linking frontal cognitive disruption and motor deficits in people with Parkinson's disease is correlational. Individuals with cognitive impairments often also display gait and balance deficits, but causal evidence remains lacking. We combined non-invasive brain stimulation with functional MRI (fMRI) to ascertain whether dorsolateral prefrontal cortex (DLPFC) exerts a causal influence modulating motor function and to test the hypothesis that an excitatory stimulation protocol applied to a cognitive control network can improve motor performance in Parkinson disease. Participants with Parkinson's disease performed a precision force-tracking task shown to track with gait impairment while undergoing functional neuroimaging scans. On half of trials, participants were required to simultaneously perform a cognitively demanding 2-back working memory task to tax attentional systems. Following the initial baseline scan, participants returned for three separate counterbalanced sessions that combined transcranial magnetic stimulation (TMS) in the form of theta burst stimulation (TBS) with fMRI. Just prior to task performance, participants received either excitatory (intermittent TBS) or inhibitory (continuous TBS) stimulation protocols over right DLPFC. In the third session, participants received stimulation to a control site outside the cognitive and motor areas implicated in our task. Our within-subjects experimental design allowed us to examine the effects of stimulation on motor behavior, the influence of cognitive load on motor behavior, and the neural systems supporting cognitive control and motor execution. Consistent with our hypothesis, excitatory stimulation of DLPFC improved motor performance in a precision force-tracking task as indexed by reduced tracking error and smoother movement execution. These effects emerged preferentially under dual-task conditions when cognitive demands were high. Our results show that this improved motor performance coincides with reductions in functional connectivity not only between the stimulation site and primary motor cortex, but also within the recently described somato-cognitive action network (SCAN) thought to support action planning and whole-body movement coordination. We conclude that frontal cognitive control systems play a causal role in modulating movement in Parkinson's disease and suggest that targeting these systems with non-invasive interventions may enhance motor function.

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bioRxiv2026

Transcranial Magnetic Stimulation Differentiates Egocentric vs. Allocentric Network Hubs for Memory-Guided Reach

Previous patient and imaging studies suggest that dorsal and ventral visual stream mechanisms contribute selectively to egocentric (eye-centred) and allocentric (landmark-centred) goal-directed behaviours, respectively. However, causal evidence for this ego-allocentric dissociation in healthy brains is lacking. Based on a recent neuroimaging study, we hypothesized that perturbations to dorsal stream network hubs would disrupt both egocentric and allocentric reaches, whereas perturbations to ventral hubs would affect only allocentric reaches. Sixteen participants viewed a briefly presented target in the presence of a landmark that later shifted after a memory interval. Participants were instructed to 1) ignore the landmark and reach toward / opposite the original target location (egocentric task) or 2) reach toward the targets location fixed relative to the shifted landmark (allocentric task). Transcranial magnetic stimulation (TMS) was applied during the memory period, spanning the landmark shift, at two occipital sites, based on the network hub coordinates from our previous study and individual brain anatomy. As predicted, superior occipital TMS impaired reaction time, accuracy, and precision in both tasks, whereas inferior occipital TMS only impaired allocentric performance. Further, spatial asymmetries in the resulting error patterns were influenced by TMS site and task: superior occipital TMS influenced asymmetries more strongly in the egocentric task, whereas inferior occipital TMS only influenced spatial asymmetries in the allocentric task. Finally, a functional network analysis revealed a widespread influence of TMS on network-behavior relations and another dissociation: greater influence of superior occipital TMS on the egocentric task and of inferior occipital TMS on the allocentric task. These results establish specific causal relationships between occipital hubs, widespread cortical networks, and reach behavior, confirming a default dorsal egocentric transformation for visually aimed reaches, and a role for the ventral stream for landmark-centred actions.

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bioRxiv2026

Cerebellar perturbation impairs human working memory and degrades spatial tuning throughout cortex

Working memory, the transient maintenance and manipulation of information, is fundamental to human cognition. While working memory is typically thought to rely on frontoparietal cortex, the cerebellum communicates with association cortex through closed-loop cerebro-cerebellar pathways and is well positioned to influence cortical dynamics supporting cognition. It is currently unknown whether cerebellar processing is causally necessary for the maintenance of visual information and whether cortical population coding is dependent on cerebellum. We combined functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) of frontal, parietal, and cerebellar cortex in humans. Using a generative model of population receptive fields, we show that cerebellar perturbation impairs spatial working memory recall and broadly degrades cortical spatial tuning. Direct comparisons revealed dissociable effects on population coding: cerebellar perturbation preferentially reduced stimulus-specific gain in early visual cortex, parietal perturbation preferentially suppressed stimulus-independent visual responses, and frontal perturbation preferentially increased response variability across higher-order visual, parietal, and frontal regions. These findings demonstrate that intact cerebellar function is necessary for maintaining cortical working memory representations and that cerebellar, parietal, and frontal nodes support working memory fidelity via distinct mechanisms.

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bioRxiv2024

Errors of attention adaptively warp spatial memory

Adaptation is the process by which we adjust internal models of the body, world, and mind in response to sensory feedback. While adaptation is studied extensively in the context of motor control, there is limited evidence that cognitive functions such as working memory are subject to the same error-driven adaptive control mechanism. To examine the possibility that internal spatial representations undergo adaptation, we had participants perform a task that interleaved a perceptual discrimination task and a spatial working memory task. Perceptual discrimination trials (85% of trials) presented an initial peripheral cue to exogenously capture attention, immediately followed by a displaced target stimulus. This sequence of events served to repeatedly induce a covert attentional allocation error. Interleaved spatial working memory trials (15% of trials) presented a stimulus at a pseudorandom peripheral location followed by a delay interval. On half of the working memory trials, the stimulus was surreptitiously presented at the same location as the initial attentional cue. We found that as attentional errors accumulated over the course of the experiment, participants spatial recall shifted to counteract the attentional error. The magnitude of this shift was proportional to the number of induced errors. Recall performance rapidly recovered following the offset of error trials. Multiple control experiments ruled out alternative explanations for these results, such as oculomotor confounds and attentional biases unrelated to error. These findings indicate that the computational mechanisms governing the adaptation of motor commands appear to similarly serve to adjust and calibrate spatial cognition.

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bioRxiv2023

Representation and Retrieval of Brain Connectivity Information derived from TMS Experiments

BackgroundTranscranial magnetic stimulation (TMS) is a painless non-invasive method that allows focal activation or deactivation of a human brain region in order to assess effects on other brain regions. As such, it has a unique role in elucidating brain connectivity during behavior and at rest. Information regarding brain connectivity derived from TMS experiments has been published in hundreds of papers but is not accessible in aggregate. ObjectiveOur objective was to identify, extract, and represent TMS-connectivity data in a graph database. This approach uses nodes connected by edges to capture the directed nature of interregional communication in the brain while also being flexible enough to contain other information about the connections, such as the source of information and details about the experiments that produced them. MethodsData related to interregional brain connectivity is first extracted from full-text publications, with creation of a table-like structure that list data of multiple types, principally the source and target brain regions, sign (excitatory/inhibitory) and latency. While machine-reading methods were explored, so far human experts have had to extract and verify data. These data are used to populate a neo4j graph database. A graphical user interface coupled with a query system allows users to search for networks and display information about connections between any two brain regions of interest. ResultsExperiments involving two TMS stimulating coils, in which one is over a putative source region and the other is over another region with a measurable effect in the body (such as the primary motor cortex) are the most straightforward to represent in the database. Even in those experiments, differing conventions for naming regions, and differing experimental parameters such as stimulation intensity and coil position, create issues for representing data from multiple studies in the same database. Other types of experiments, such a neuromodulatory stimulation such as rTMS, can provide information regarding connectivity, but are harder to represent. But we have, thus far, stored information about 100 connections in the database and demonstrated its utility in exploring direct and indirect connections between brain regions. We have also explored adding a causal inference method to those connections, allowing information about latency to shape the connections retrieved given latency limits. ConclusionA graph database can flexibly store information about interregional brain connectivity and is particularly useful for exploring the temporal aspects of brain networks.

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bioRxiv2020

Reversal of visual feedback modulates somatosensory plasticity

Reversed visual feedback during unimanual training increases transfer of skills to the opposite untrained hand and modulates plasticity in motor areas of the brain. However, it is unclear if unimanual training with reversed visual feedback also affects somatosensory areas. Here we manipulated visual input during unimanual training using left-right optical reversing spectacles and tested whether unimanual training with reversed vision modulates somatosensory cortical excitability to facilitate motor performance. Thirty participants practiced a unimanual ball-rotation task using the right hand with either left-right reversed vision (incongruent visual and somatosensory feedback) or direct vision (congruent feedback) of the moving hand. We estimated cortical excitability in primary somatosensory cortex (S1) before and after unimanual training by measuring somatosensory evoked potentials (SEPs). This was done by electrically stimulating the median nerve in the wrist while participants rested, and recording potentials over both hemispheres using electroencephalography. Performance of the ball-rotation task improved for both the right (trained) and left (untrained) hand after training across both direct and reversed vision conditions. Participants with direct vision of the right hand during training showed SEPs amplitudes increased bilaterally. In contrast, participants in the reversed visual condition showed attenuated SEPs following training. The results suggest that cortical suppression of S1 activity supports skilled motor performance after unimanual training with reversed vision, presumably by sensory gating of afferent signals from the movement. This finding provides insight into the mechanisms by which visual input interacts with the sensorimotor system and induces neuroplastic changes in S1 to support skilled motor performance.

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bioRxiv2017

Changes in corticospinal excitability associated with motor learning by observing

While many of our motor skills are acquired through physical practice, we can also learn how to make movements by observing others. For example, individuals can learn how to reach in novel dynamical environments ( force fields, FF) by observing the movements of a tutor. Previous neurophysiology and neuroimaging studies in humans suggest a role for the motor system in motor learning by observing. Here we tested the role of primary motor cortex (M1) in motor learning by observing. We used single-pulse transcranial magnetic stimulation (TMS) to elicit motor evoked potentials (MEPs) in right hand muscles at rest. MEPs were elicited before and after participants observed either a video adapting her reaches to a FF or a control video showing a tutor performing reaches in an unlearnable FF. We predicted that observing motor learning would increase M1 excitability to a greater extent than observing movements that did not involve learning. We found that observing FF learning increased MEP amplitudes recorded from right first dorsal interosseous (FDI) and right abductor pollicis brevis (APB) muscles. There were no changes in MEP amplitudes for control participants who observed a tutor performing reaches in an unlearnable, randomly varying FF. The observed MEP changes can thus be specifically linked to observing motor learning. These results are consistent with the idea that observing motor learning produces functional changes in M1, or corticospinal networks or both.

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