Biology subjects

Wassermann, E. M.

Publications and source records attributed to Wassermann, E. M..

4 recordsLinked to original sources

bioRxiv2024

Combined effects of pharmacological interventions and intermittent theta-burst stimulation on motor sequence learning

Drugs that modulate N-methyl-D-aspartate (NMDA) or {gamma}-Aminobutyric acid type A (GABAA) receptors can shed light on their role in synaptic plasticity mechanisms underlying the effects of non-invasive brain stimulation. However, research on the combined effects of these drugs and exogenous stimulation on motor learning is limited. This study aimed to investigate the effects of pharmacological interventions combined with intermittent theta-burst stimulation (iTBS) on human motor learning. Nine right-handed healthy subjects (mean age {+/-} SD: 31.56 {+/-} 12.96 years; 6 females) participated in this double-blind crossover study. All participants were assigned to four drug conditions in a randomized order: (1) D-cycloserine (partial NMDA receptor agonist), (2) D-cycloserine + dextromethorphan (NMDA receptor agonist + antagonist), (3) lorazepam (GABAA receptor agonist), and (4) placebo (identical microcrystalline cellulose capsule). After drug intake, participants practiced the 12-item keyboard sequential task as a baseline measure. Two hours after drug intake, iTBS was administered at the primary motor cortex. Following iTBS, the retention test was performed in the same manner as the baseline measure. Our findings revealed that lorazepam combined with iTBS impaired motor learning during the retention test. Future studies are still needed for a better understanding of the mechanisms through which TMS may influence human motor learning.

neuroscience↗

bioRxiv2021

Dynamic changes in spatial representation within the posterior parietal cortex in response to visuomotor adaptation

Recent studies used fMRI population receptive field (pRF) mapping to demonstrate that retinotopic organization extends from primary visual cortex to ventral and dorsal visual pathways by quantifying visual field maps, receptive field size, and laterality throughout multiple areas. Visuospatial representation in the posterior parietal cortex (PPC) is modulated by attentional deployment, raising the question of whether spatial representation in the PPC is dynamic and flexible and that this flexibility contributes to visuospatial learning. To answer this question, changes in spatial representation within PPC, as measured with pRF mapping, were recorded before and after visuomotor adaptation. Visuospatial input was laterally manipulated, rightward or leftward, via prism adaptation, a well-established visuomotor technique that modulates visuospatial performance. Based on existing models of prism adaptation mechanism of action, we predicted left prism adaptation to produce a right visuospatial bias via an increasing pRF size in the left parietal cortex. However, our hypothesis was agnostic as to whether right PPC will show an opposite effect given the bilateral bias to right visual field. Findings show that adaptation to left-shifting prisms increases pRF size in both PPCs, while leaving space representation in early visual cortex unchanged. This is the first evidence that prism adaptation drives a dynamic reorganization of response profiles in the PPC. Our results show that spatial representation in the PPC not only reflects changes driven by attentional deployment but dynamically changes in response to visuomotor adaptation. Furthermore, our results provide support for using prism adaptation as a tool to rehabilitate visuospatial deficits. SIGNIFICANCE STATEMENTRepresentation of space in the posterior parietal cortex (PPC) is reflective of attentional selection. Deploying attention to a certain spatial location modulates response profiles of a corresponding set of neurons with receptive fields in the corresponding spatial location. Here, we show that visuomotor adaptation accomplished through left-shifting prism adaptation dynamically changes the representation of space in the PPC while preserving early visual representations. This is the first evidence that visuomotor adaptation drives an instant reorganization of spatial representation in PPC. This result has implications for understanding the dynamic organization of spatial representation in the PPC and for the rehabilitation of patients with neglect syndrome, whose spatial attention is compromised.

neuroscience↗

bioRxiv2020

Callosal anisotropy predicts attentional network changes after parietal inhibitory stimulation

Hemispatial neglect is thought to result from disruption of interhemispheric equilibrium. Right hemisphere lesions deactivate the right frontoparietal network and hyperactivate the left via release from interhemispheric inhibition. Support for this theory comes from neuropsychological evidence as well as transcranial magnetic stimulation (TMS) studies in healthy subjects, in whom right posterior parietal cortex (PPC) inhibition causes neglect-like, rightward, visuospatial bias. Concurrent TMS and fMRI after right PPC TMS show task-dependent changes but may fail to identify effects of stimulation in areas not directly activated by the specific task, complicating interpretations. We used resting-state functional connectivity (RSFC) after inhibitory TMS over the right PPC to examine changes in the networks underlying visuospatial attention. In a crossover experiment in healthy individuals, we delivered continuous theta burst TMS to the right PPC and vertex as control condition. We hypothesized that PPC inhibitory stimulation would cause a rightward visuospatial bias, decrease PPC connectivity with frontal areas, and increase PPC connectivity with the attentional network in the left hemisphere. We also expected that individual differences in fractional anisotropy (FA) in white matter connections between the PPCs would account for variability in TMS-induced RSFC changes. As expected, TMS over the right PPC caused a rightward shift in line bisection judgment and increased RSFC between the right PPC and the left superior temporal gyrus. This effect was inversely related to FA in the posterior corpus callosum. Local inhibition of the right PPC reshapes connectivity in the attentional network and depends on interhemispheric connections.

neuroscience↗

bioRxiv2019

Identifying site- and stimulation-specific TMS-evoked EEG potentials using a quantitative cosine similarity metric

The ability to interpret transcanial magnetic stimulation (TMS) evoked EEG potentials (TEPs) is limited by artifacts, such as auditory evoked responses produced by the TMS coil. TEPs generated from direct cortical stimulation should vary in spatial distribution with stimulation site and from responses to sham stimulation. Responses that do not show these effects are likely to be artifactual. In 20 healthy volunteers, we delivered active and sham TMS to right prefrontal, left primary motor, and left posterior parietal cortex and compared the waveform similarity of TEPs between stimulation sites and active and sham TMS with a cosine similarity-based analysis method. We looked for epochs after the stimulus when the spatial pattern of TMS-evoked activation had greater than random similarity between stimulation sites and sham vs. active TMS, indicating presence of a dominant artifact, such as the auditory brain response. We calculated and binarized the derivatives of the TEPs recorded from 30 EEG channels and calculated cosine similarity between conditions at each time point with millisecond resolution. Only TEP components occurring before approximately 80 ms differed across stimulation sites and between active and sham, indicating site and condition-specific responses. TEP components before about 80 ms can be safely interpreted as stimulation location-specific responses to TMS, but components beyond this latency should be interpreted with caution due to high similarity in their spatial distribution.

neuroscience↗