Biology subjects

Suresh, T.

Publications and source records attributed to Suresh, T..

7 recordsLinked to original sources

bioRxiv2026

Micro-offline gains do not drive implicit motor sequence learning

Motor sequence performance improves during and between brief practice bouts (micro-online and offline gains). We compared both metrics across two groups: one exposed to an implicit motor sequence, and one not. Micro-online gains drove sequence-specific learning and positively correlated with overall skill. However, micro-offline gains were comparable between groups and did not track sequence-specific learning. We conclude that implicit motor sequence learning is driven by micro-online rather than micro-offline gains.

neuroscience↗

bioRxiv2026

Resting bilateral sensorimotor mu rhythm suppression facilitates ipsilesional M1 excitability after stroke

ObjectiveStroke-related corticospinal tract (CST) disruption causes lasting hand impairments, but many stroke survivors retain some residual CST connections. In neurotypical adults, motor cortex (M1) TMS interventions can strengthen CST transmission when coupled to EEG brain states reflecting heightened M1 excitability. Because stroke alters the relationship between these brain states and cortical excitability, we aimed to identify poststroke brain states that accurately capture ipsilesional M1 excitability. We hypothesized that heightened ipsilesional M1 excitability would be represented by a common, group-level EEG pattern and a participant- specific, personalized pattern. MethodsWe acquired single-pulse TMS-EEG-EMG datasets in 15 chronic stroke survivors with residual CST connections. We then identified group-level and individual-specific EEG power patterns that distinguished between high and low ipsilesional M1 excitability states. ResultsAt the group level, bilateral sensorimotor mu power was significantly suppressed during high versus low excitability states, but this suppression did not correlate with hand impairment severity or trait-level ipsilesional M1 excitability. At the individual level, spatiotemporally varied EEG activity patterns distinguished between excitability states, but these patterns were only present in 60% of individuals. Conclusion and SignificanceThis study is the first to systematically characterize poststroke EEG brain states reflecting ipsilesional M1 excitability. Findings suggest that individual-specific EEG patterns may inconsistently index ipsilesional M1 excitability and instead identify bilateral sensorimotor mu power suppression as a group-level excitability marker that is present across the full spectrum of poststroke hand impairment. HighlightsO_LIWe analyzed TMS-EEG-EMG to identify group and individual level ipsilesional motor cortical excitability states in chronic stroke C_LIO_LIBilateral sensorimotor mu suppression marked heightened ipsilesional motor cortical excitability across hand impairment severity C_LIO_LI60% participants had individual level scalp patterns linked to motor cortical excitability states, challenging their reliability C_LI

neuroscience↗

bioRxiv2026

Incorporating motor preparation time transforms micro-offline gains into micro-offline losses

During explicit sequence learning (ESL), micro-offline gains (MOGS) occur during brief rest periods. MOGS are calculated as the difference in keypresses-per-second (KPS) between the first sequence of one trial and the last sequence of the preceding trial. To date, all studies evaluating MOGS have calculated KPS from the motor execution time (MET) that occurs between keypresses, but this approach ignores potential contributions from motor preparation which occur prior to the first keypress. Given that ESL relies on both pre-movement motor planning and subsequent motor execution, we hypothesized that ignoring motor preparation time (MPT) neglects a critical component of skill acquisition, potentially misrepresenting the true magnitude of MOGS. To test this, we calculated MOGS with and without MPT in thirty adults who performed an ESL task. Our results show that including MPT flipped MOGS from positive to negative and significantly increased the positive correlation between early learning and a gold-standard ESL metric: the number of correct sequences performed. Our results suggest that MPT should be incorporated into MOGS calculations and that excluding it overestimates micro-offline learning.

neuroscience↗

bioRxiv2025

REACTIVATION PROTECTS HUMAN MOTOR MEMORIES AGAINST INTERFERENCE FROM COMPETING INPUTS

Memories are often thought to become increasingly stable and resistant to change over time. The reconsolidation framework proposes that reactivating a stable memory transiently increases its susceptibility to modification by subsequent experience, but evidence for such reactivation-induced destabilization remains mixed. Here we tested whether reactivation alters the susceptibility of a visuomotor memory to interference from competing learning. Across a series of motor adaptation experiments, we briefly reactivated a previously acquired memory before introducing an opposing perturbation. Contrary to reconsolidation predictions, reactivation did not increase interference during later retrieval. Instead, reactivation reduced interference when the competing memory was not allowed to stabilize after acquisition. Our findings challenge the view that reactivation universally destabilizes motor memories and instead suggest that it shapes which competing motor memory is expressed at retrieval.

neuroscience↗

bioRxiv2024

Motor sequence learning-induced corticospinal plasticity is biased towards sensorimotor mu rhythm peak phases

Motor cortical (M1) transcranial magnetic stimulation (TMS) interventions increase corticospinal output and improve motor learning when delivered during sensorimotor mu rhythm trough but not peak phases, suggesting that the mechanisms supporting motor learning may be most active during mu trough phases. Based on these findings, we predicted that motor sequence learning-related corticospinal plasticity would be most evident when measured during mu trough phases. Healthy adults were assigned to either a sequence or no-sequence group. Participants in the sequence group practiced the implicit serial reaction time task (SRTT), which contained an embedded, repeating 12-item sequence. Participants in the no-sequence group practiced a version of the SRTT that contained no sequence. We measured mu phase-independent and mu phase-dependent MEP amplitudes using EEG-informed single-pulse TMS before, immediately after, and 30 minutes after the SRTT in both groups. All participants performed a retention test one hour after SRTT acquisition. In both groups, mu phase-independent MEP amplitudes increased following SRTT acquisition, but the pattern of mu phase-dependent MEP amplitude changes after SRTT acquisition differed between groups. Relative to the no-sequence group, the sequence group showed greater peak-specific MEP amplitude increases 30 minutes after SRTT acquisition. Further, the magnitude of these peak-specific MEP amplitude increases was negatively associated with the magnitude of sequence-specific learning. Contrary to our original hypothesis, results revealed that motor sequence-specific learning elicits peak-specific corticospinal plasticity. Findings provide first direct evidence for the presence of a mu phase-dependent motor learning mechanism in the human brain. New and NoteworthyRecent work suggests that motor learnings neural mechanisms may be most active during specific sensorimotor mu rhythm phases. If so, motor sequence learning-induced corticospinal plasticity should be more evident during some mu phases than others. Our results show that motor sequence-specific learning elicits corticospinal plasticity that is most prominent during mu peak phases. Further, this peak-specific plasticity correlates with learning. Findings establish the presence of a mu phase-dependent motor learning mechanism in the human brain.

neuroscience↗

bioRxiv2022

Over-expression of thyroid hormone receptor β2 in zebrafish changes the distribution of cone spectral signals

Zebrafish retinal cone signals shift in spectral shape through larval, juvenile, and adult development as expression patterns of eight cone-opsin genes change. An algorithm extracting signal amplitudes for the component cone spectral types is developed and tested on two thyroxin receptor {beta}2 (tr{beta}2) gain-of-function lines crx:mYFP-2A-tr{beta}2 and gnat2:mYFP-2A-tr{beta}2, allowing correlation between opsin signaling and opsin immunoreactivity in lines with different developmental timing and cell-type expression of this red-opsin-promoting transgene. Both adult transgenics became complete, or nearly complete, red-cone dichromats, with disproportionately large LWS1 opsin amplitudes as compared to controls, where LWS1 and LWS2 amplitudes were about equal, and significant signals from SWS1, SWS2, and Rh2 opsins were detected. But in transgenic larvae and juveniles of both lines it was LWS2 amplitudes that increased, with LWS1 cone signals rarely encountered. In gnat2:mYFP-2A-tr{beta}2 embryos at 5 days post fertilization (dpf), red-opsin immunoreactive cone density doubled, but red-opsin amplitudes (LWS2) increased < 10%, and green, blue and UV opsin signals were unchanged, despite co-expressed red opsins, and the finding that an sws1 UV-opsin reporter gene was shut down by the gnat2:mYFP-2A-tr{beta}2 transgene. By contrast both LWS2 red-cone amplitudes and the density of red-cone immunoreactivity more than doubled in 5 dpf crx:mYFP-2A-tr{beta}2 embryos, while UV-cone amplitudes were reduced 90%. Embryonic cones with tr{beta}2 gain-of-function transgenes were morphologically distinct from control red, blue or UV cones, with wider inner segments and shorter axons than red cones, suggesting cone spectral specification, opsin immunoreactivity and shape are influenced by the abundance and developmental timing of tr{beta}2 expression. Significance StatementAs different combinations of eight cone-opsin mRNAs are successively expressed during zebrafish development and maturation, the composite cone-ERG spectral signal shifts. Amplitudes of each of the eight resulting cone signals are inferred computationally from the composite signal, both in controls and in two thyroxin-receptor {beta}2 (tr{beta}2) gain-of-function transgenics, crx:mYFP-2A-tr{beta}2 and gnat2:mYFP-2A-tr{beta}2, tr{beta}2 being a transcription factor required for expression of the red-cone opsins LWS1 and LWS2. Adult transgenics become red cone dichromats with excess LWS1 amplitudes, but larvae and juveniles evoke excess LWS2 amplitudes. Controls retain 5 to 6 cone signals of changing composition throughout development. The progression of transgene-induced amplitude alterations is slower in gnat2:mYFP-2A-tr{beta}2, with supernormal red-opsin antigenicity not immediately correlating with red-cone signaling.

neuroscience↗

bioRxiv2020

The Effect of Refractive Blur in the Vividness of Mental Imagery

BackgroundVisual mental imagery or "seeing with the minds eye" is an everyday phenomenon. Visual mental imagery and visual perception share common neural-networks. Hence deficits that affect the visual perception may also affect visual mental imagery. AimWe aimed to study the effect of refractive blur on the vividness of mental imagery. MethodsSubjects were recruited from volunteers and divided into two groups; individuals with refractive errors-Ametropes(AM), and individuals without refractive errors - Emmetropes(EM). After filling in the Verbalizer-Visualizer-Questionnaire (VVQ), the subjects were asked to perform a mental imagery task with and without refractive blur. The participants were asked to generate a mental image of a specific object initially with eyes closed, eyes open and then with refractive blur in random order, and then judge the vividness of the mental image on a Likert scale ranging from 1 (low vividness) to 5 (good vividness). The EM participants had to wear a + 2D spectacles to produce refractive blur. ResultsA total of 162 participants were recruited to the study. Of these 73 were EM and 89 were AM. Of the AM, 30 had additional astigmatism. The mean VVQ score was 64.9(11.2). The mean refractive error was 1.8(1.3)D. Following the mental imagery task, at baseline with eyes closed, 138 (85.5%)subjects had vivid mental imagery close to visual perception(Likert scale:5). With the opening of the eyes, the vividness dropped by at least 1 point in the Likert scale in 139(85.8%). With the introduction of refractive blur, 153(94.4%) subjects had a drop in the vividness of the image by at least 1 point and 22(13.6%) subjects by at least 2 points. ConclusionIntroduction of refractory blur results in the reduction of the vividness of mental imagery.

neuroscience↗