Biology subjects

Vallence, A.-M.

Publications and source records attributed to Vallence, A.-M..

5 recordsLinked to original sources

bioRxiv2024

Dual-site transcranial alternating current stimulation over the primary motor cortices increases interhemispheric inhibition and improves bimanual dexterity: A triple-blind, randomised, sham-controlled study

Concurrent application of transcranial alternating current stimulation (tACS) over distant cortical regions has been shown to modulate functional connectivity between stimulated regions; however, the precise mechanisms remain unclear. Here, we investigated how dual-site tACS (ds-tACS) applied over the bilateral primary motor cortices (M1s) modulates connectivity between M1s. Using a cross-over sham-controlled triple-blind within- subject design, 37 (27 female, age 18-37yrs) healthy participants received tACS (1.0mA, 20Hz) over the bilateral M1s for 20 min. Before and after tACS, functional connectivity between M1s was assessed using imaginary coherence (ImCoh) measured via resting-state electroencephalography (EEG) and interhemispheric inhibition (IHI) via dual-site transcranial magnetic stimulation (TMS) protocol. Additionally, manual dexterity was assessed using the Purdue pegboard task. While ImCoh remained unchanged after simulation, spectral power analysis showed a significant decrease in beta (20 Hz) power during the tACS session. ds-tACS but not sham strengthened IHI between the M1s and improved bimanual assembly performance. These results suggest that improvement in bimanual performance may be explained by modulation in M1-M1 IHI, rather than by coupling in the oscillatory activity. As functional connectivity underlies many clinical symptoms in neurological and psychiatric disorders, these findings are invaluable in developing non-invasive therapeutic interventions that target neural networks to alleviate symptoms.

neuroscience↗

bioRxiv2023

From Inhibition to Excitation and Why: The Role of Temporal Urgency in Modulating Corticospinal Activity

Previous research on movement preparation identified a period of corticospinal suppression about 200 ms prior to movement initiation. This phenomenon has been observed for different types of motor tasks typically used to investigate movement preparation (e.g., reaction time, self-initiated, and anticipatory actions). However, we recently discovered that this phenomenon is not observed when actions must be initiated under time pressure. In the present study, we investigated urgency effects on corticospinal suppression throughout the time course of an anticipatory timing task. Participants were required to perform timing actions under two urgency scenarios, high and low, and we applied single-pulse transcranial magnetic stimulation at different times during the time course of preparation. We analysed the time course of excitability under high and low scenarios in relation to expected and actual movement onset times. Our results confirmed our earlier findings that corticospinal suppression is not observed when participants perform actions under high urgency scenarios. In addition, we found no evidence that this preparatory suppression could be shifted in time to occur later under high urgency scenarios. Moreover, we found evidence that responses prepared under high urgency are more likely to be disrupted by external events (e.g., TMS pulses). These results suggest that preparatory suppression might be a strategy employed by the central nervous system to shield motor actions from interference of external events (e.g., loud sounds) when time allows. Given these data, we propose conceptual models that could account for the absence of preparatory suppression under time pressure to act.

neuroscience↗

bioRxiv2021

Premovement inhibition protects motor actions from interference

Shortly before movement initiation, the corticospinal system undergoes a transient suppression. This phenomenon has been observed across a range of motor tasks, suggesting that it may be a obligatory component of movement preparation. We probed whether this was also the case when the urgency to perform a motor action was high, in a situation where little time was available to engage in preparatory processes. We controlled the urgency of an impending motor action by increasing or decreasing the foreperiod duration in an anticipatory timing task. Transcranial magnetic stimulation (TMS; experiment one) or a loud acoustic stimulus (LAS; experiment two) were used to examine how corticospinal and subcortical excitability were modulated during motor preparation. Preparatory inhibition of the corticospinal tract was absent when movement urgency was high, though motor actions were initiated on time. In contrast, subcortical circuits were progressively inhibited as the time to prepare increased. Interestingly, movement force and vigour were reduced by both TMS and the LAS when movement urgency was high, and enhanced when movement urgency was low. Our findings indicate that preparatory inhibition may not be a obligatory component of motor preparation. The behavioural effects we observed in the absence of preparatory inhibition were induced by both TMS and the LAS, suggesting that accessory sensory stimulation may disrupt motor output when such stimulation is presented in the absence of preparatory inhibition. We conclude that preparatory inhibition may be an adaptive strategy which can serve to protect the prepared motor action from external interference.

neuroscience↗

bioRxiv2019

Characterising the balance between short-interval intracortical inhibition and short-interval intracortical facilitation in younger and older adults.

News and noteworthyO_LIMeasures of short-interval intracortical inhibition (SICI) and facilitation (SICF) reflect a balance between the excitability of inhibitory and facilitatory circuits in the motor cortex.\nC_LIO_LISICI stimulus-response functions, measured with a range of conditioning stimulus intensities and two intervals (first peak and trough of the SICF function), were similar between younger and older adults, except at the shift from net inhibition to facilitation.\nC_LIO_LIRelationships between SICI and SICF and manual dexterity show that an inhibition-facilitation balance favouring inhibition is associated with better manual dexterity and a balance favouring facilitation is associated with poorer manual dexterity.\nC_LI\n\nAbstractResearch investigating age-related differences in intracortical inhibition acting within the primary motor cortex (M1) reports inconsistent results. Age-related changes in the balance of inhibition and facilitation acting within M1 might underlie the inconsistent findings. Here, paired-pulse TMS was used to examine the balance between short-interval intracortical inhibition (SICI) and short-interval intracortical facilitation (SICF) in younger (n=26) and older (n=21) adults. First, the inter-stimulus intervals (ISIs) that produced maximal and minimal SICF at the first peak and trough were identified for each individual. Second, SICI stimulus-response functions (conditioning stimulus (CS): 50-110% resting motor threshold) were determined at ISIs that produced maximal and minimal facilitation for each individual. When SICI was measured with the ISI that produced maximal facilitation, the shift from net inhibition to net facilitation occurred at a lower CS intensity in older than younger adults. When SICI was measured with the ISI that produced minimal facilitation, older adults showed a persistent net inhibition at the highest CS intensity, whereas younger adults showed a shift from net inhibition to net facilitation at high CS intensities. Relationships between SICI and SICF and manual dexterity were evident across all measures of the inhibition-facilitation balance, whereby a balance favouring inhibition is associated with better manual dexterity and a balance favouring facilitation is associated with poorer manual dexterity. These findings contribute to our understanding of age-related differences in intracortical inhibitory and facilitatory processes, as well as highlight the importance of considering the balance between inhibitory and facilitatory processes when measuring SICI and SICF.

neuroscience↗

bioRxiv2018

A data-driven approach to reduce gender disparity in invited speaker programs at scientific meetings

We present a data-driven approach that uses established metrics of scientific quality to select invited speakers; this approach enables gender parity in conference programs while ensuring high scientific standards. Gender disparity continues to be an issue in STEM, with progress requiring consistent and focused efforts. Here, we present a data-driven approach to promote high quality, gender balanced invited speaker selection for neuroscience conferences. We have targeted invited speaker opportunities because underrepresentation of female speakers at international neuroscience conferences remains a major problem, and such opportunities are critical for career development. First, we audited the top ten neuroscience journals (indexed by SCImago Journal and Country Rank; SJR), identifying (1) highly cited papers, (2) gender of first and last authors, and (3) field-weighted citation impact and total publications of first and last authors. Second, we used these data to establish a database of high quality scientists that could be used to select speakers for conferences. We found that research quality (as indexed by field-weighted citation impact and total publications) of authors of highly cited publications in the top 10 neuroscience journals did not differ significantly for females and males. The comparison between the gender base rate in neuroscience and authors publishing highly cited papers in high-quality neuroscience journals shows that female representation, particularly at last author level, is less than the estimated base rate for neuroscience. In summary, we present a data-driven approach to invited speaker selection that would facilitate gender balanced conference programs while maintaining the highest of scientific standards. This approach minimizes the influence of implicit gender bias in speaker selection decisions by using scientific quality metrics that STEM researchers are familiar with, and indeed use to evaluate their own performance. Having an immediate effect on reducing gender disparity in conference programs, our approach would generate a positive spiral for more long-term reduction of gender disparity in STEM.

scientific communication and education↗