Biology subjects

Gann, M. A.

Publications and source records attributed to Gann, M. A..

6 recordsLinked to original sources

bioRxiv2025

Dual-site beta transcranial alternating current stimulation during a bimanual coordination task modulates functional connectivity between motor areas

BackgroundCommunication within brain networks depends on functional connectivity. One promising approach to modulate such connectivity between cortical areas is dual-site transcranial alternating current stimulation (tACS), which non-invasively applies weak alternating currents to two brain areas. Objectives/HypothesesIn the current study, we aimed to modulate inter-regional functional connectivity with dual-site tACS to bilateral primary motor cortices (M1s) during bimanual coordination and, in turn, alter behaviour. MethodsUsing functional magnetic resonance imaging (fMRI), we recorded participants brain responses during a bimanual coordination task in a concurrent tACS-fMRI design. While performing a slow and fast version of the task, participants received one of three types of beta (20 Hz) dual-site tACS over both M1s: in-phase, jittered-phase or sham, in a within-subject, repeated measures design. ResultsWhile we did not observe any significant tACS effects on behaviour, the study revealed a disruptive effect of in-phase tACS on interhemispheric connectivity. Additionally, the two active types of tACS (in-phase and jittered-phase) differed in the task-related M1 connectivity with other motor cortical regions, such as premotor cortex and supplementary motor area. Furthermore, individual E-field strengths were related to functional connectivity in the in-phase condition. ConclusionsDual-site beta tACS over both M1s altered functional connectivity between motor areas. However, this effect did not translate to the behavioural level, possibly due to compensatory mechanisms. HighlightsO_LIInterhemispheric connectivity between the primary motor cortices was targeted with dual-site beta tACS during bimanual coordination. C_LIO_LIIn-phase as compared to sham tACS disrupted interhemispheric connectivity during task performance. C_LIO_LIIn-phase and jittered-phase tACS led to different task-related functional connectivity patterns within the motor network. C_LIO_LIThe relationship between individual in-phase E-field strengths and interhemispheric connectivity depended on task demand. C_LIO_LIThere were no significant tACS effects on behavioural performance of bimanual coordination, possibly due to compensatory mechanisms. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/647211v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@17ecdd8org.highwire.dtl.DTLVardef@1fc5b25org.highwire.dtl.DTLVardef@c3df42org.highwire.dtl.DTLVardef@17671bb_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2022

Prefrontal stimulation disrupts motor memory consolidation at the micro timescale

Functional brain responses in hippocampo- and striato-cortical networks during initial motor sequence learning (MSL) are critical for memory consolidation. We have recently shown that prefrontal stimulation applied prior to initial MSL can alter these learning-related responses. In the present study, we investigated whether such stimulation-induced modulations of brain responses can influence motor memory consolidation at different timescales. Specifically, we examined the effect of prefrontal stimulation on the behavioral and neural responses associated to (i) fast consolidation processes occurring during short rest episodes interspersed with practice during initial learning (i.e., micro timescale) and (ii) slow consolidation process taking place across practice sessions separated by 24h (i.e., macro timescale). To do so, we applied active (inhibitory or facilitatory) or control theta-burst stimulation to the prefrontal cortex of young healthy participants before they were trained on an MSL task while their brain activity was recorded using functional magnetic resonance imaging (fMRI). Motor performance was retested, in the MRI scanner, after a night of sleep. Both our behavioral and brain imaging results indicate that while stimulation did not modulate consolidation at the macro timescale, it disrupted the micro-offline consolidation process. Specifically, our behavioral data indicate that active - as compared to control - stimulation resulted in a decrease in micro-offline gains in performance over the short rest intervals. At the brain level, stimulation disrupted activity in the caudate nucleus and the hippocampus during the micro-offline intervals. Additionally, multivariate pattern persistence from task into inter-practice rest episodes - which is thought to reflect the reactivation of learning-related patterns - was hindered by active prefrontal stimulation in the hippocampus and caudate nucleus. Importantly, stimulation also altered the link between the brain and the behavioral markers of the micro-offline consolidation process. These results collectively suggest that active prefrontal stimulation prior to MSL disrupted both the behavioral and neural correlates of motor memory consolidation at the micro timescale.

neuroscience↗

bioRxiv2021

Prefrontal stimulation prior to motor sequence learning alters multivoxel patterns in the striatum and the hippocampus

Motor sequence learning (MSL) is supported by dynamical interactions between hippocampal and striatal networks that are thought to be orchestrated by the prefrontal cortex. In the present study, we tested whether individually-tailored theta-burst stimulation of the dorsolateral prefrontal cortex (DLPFC) prior to MSL, can modulate multivoxel response patterns in the stimulated cortical area, the hippocampus and the striatum. Response patterns were assessed with multivoxel correlation structure analyses of functional magnetic resonance imaging data acquired during task practice and during resting-state scans before and after learning/stimulation. Results revealed that, across stimulation conditions, MSL induced greater modulation of task-related DLPFC multivoxel patterns than random practice. A similar learning-related modulatory effect was observed on sensorimotor putamen patterns under inhibitory stimulation. Furthermore, MSL as well as inhibitory stimulation affected (posterior) hippocampal multivoxel patterns at post-intervention rest. Exploratory analyses showed that MSL-related brain patterns in the posterior hippocampus persisted into post-learning rest preferentially after inhibitory stimulation. These results collectively show that prefrontal stimulation can alter multivoxel brain patterns in deep brain regions that are critical for the MSL process. They also suggest that stimulation influenced early offline consolidation processes as evidenced by a stimulation-induced modulation of the reinstatement of task pattern into post-learning wakeful rest.

neuroscience↗

bioRxiv2021

Persistence of Hippocampal and Striatal Multivoxel Patterns during Awake Rest after Motor Sequence Learning

Memory consolidation, the process by which newly encoded and fragile memories become more robust, is thought to be supported by the reactivation of brain regions - including the hippocampus - during post-learning rest. While hippocampal reactivations have been demonstrated in humans in the declarative memory domain, it remains unknown whether such a process takes place after motor learning. Using multivariate analyses of task-related and resting state fMRI data, here we show that patterns of brain activity within both the hippocampus and striatum elicited during motor learning persist into post-learning rest, indicative of reactivation of learning-related neural activity patterns. Moreover, results indicate that hippocampal reactivation reflects the spatial representation of the learned motor sequence. These results thus provide insights into the functional significance of neural reactivation after motor sequence learning.

neuroscience↗

bioRxiv2020

Hippocampal and striatal responses during motor learning are modulated byprefrontal cortex stimulation

While it is widely accepted that motor sequence learning (MSL) is supported by a prefrontal-mediated interaction between hippocampal and striatal networks, it remains unknown whether the functional responses of these networks can be modulated in humans with targeted experimental interventions. The present proof- of-concept study employed a comprehensive multimodal neuroimaging approach, including functional magnetic resonance (MR) imaging and MR spectroscopy, to investigate whether individually-tailored theta-burst stimulation of the dorsolateral prefrontal cortex can modulate responses in the hippocampus and striatum during motor learning. Our results indicate that stimulation influenced task-related connectivity patterns within hippocampo-frontal and striatal networks. Stimulation also altered the relationship between the levels of gamma-aminobutyric acid (GABA) in the stimulated prefrontal cortex and learning-related changes in both activity and connectivity in fronto-striato-hippocampal networks. This study provides the first experimental evidence that brain stimulation can alter motor learning-related functional responses in the striatum and hippocampus.

neuroscience↗

bioRxiv2019

Sensorimotor expectations bias motor resonance during observation of object lifting: The causal role of pSTS

Transcranial magnetic stimulation (TMS) studies have highlighted that corticospinal excitability (CSE) is increased during observation of object lifting, an effect termed motor resonance. This facilitation is driven by movement features indicative of object weight, such as object size or observed movement kinematics. Here, we investigated in 35 humans (23 females) how motor resonance is altered when the observers weight expectations, based on visual information, do not match the actual object weight as revealed by the observed movement kinematics. Our results highlight that motor resonance is not robustly driven by object weight but easily masked by a suppressive mechanism reflecting the correctness of the weight expectations. Subsequently, we investigated in 24 humans (14 females) whether this suppressive mechanism was driven by higher-order cortical areas. For this, we induced virtual lesions to either the posterior superior temporal sulcus (pSTS) or dorsolateral prefrontal cortex (DLPFC) prior to having participants perform the task. Importantly, virtual lesion of pSTS eradicated this suppressive mechanism and restored object weight-driven motor resonance. In addition, DLPFC virtual lesion eradicated any modulation of motor resonance. This indicates that motor resonance is heavily mediated by top-down inputs from both pSTS and DLPFC. Altogether, these findings shed new light on the theorized cortical network driving motor resonance. That is, our findings highlight that motor resonance is not only driven by the putative human mirror neuron network consisting of the primary motor and premotor cortices as well as the anterior intraparietal sulcus, but also by top-down input from pSTS and DLPFC. Significance StatementObservation of object lifting activates the observers motor system in a weight-specific fashion: Corticospinal excitability is larger when observing lifts of heavy objects compared to light ones. Interestingly, here we demonstrate that this weight-driven modulation of corticospinal excitability is easily suppressed by the observers expectations about object weight and that this suppression is mediated by the posterior superior temporal sulcus. Thus, our findings show that modulation of corticospinal excitability during observed object lifting is not robust but easily altered by top-down cognitive processes. Finally, our results also indicate how cortical inputs, originating remotely from motor pathways and processing action observation, overlap with bottom-up motor resonance effects.

neuroscience↗