Premotor-Motor interhemispheric inhibition is released during movement initiation in older but not young adults

Neural interactions between contralateral motor regions are thought to be instrumental in the successful preparation, and execution, of volitional movements. Here we investigated whether healthy ageing is associated with a change in functional connectivity, as indicated by the ability to modulate interhemispheric interactions during movement preparation in a manner that assists rapid movement responses. Thirteen young (mean age 22.2 years) and thirteen older (68.5 years) adults rapidly abducted their left index finger as soon as possible in response to a visual imperative signal, presented 500 ms after a visual warning signal. Interactions between left dorsal premotor cortex (LPMd) and right primary motor cortex (RM1) and between left primary motor cortex (LM1) and RM1 were investigated at six time points between the warning signal and the volitional response using paired-pulse transcranial magnetic stimulation. Relative to the inhibitory interactions measured at rest, both young and older adults released LM1-RM1 inhibition beginning 250 ms after the warning signal, with no significant differences between groups. LPMd-RM1 interactions became facilitatory (from the onset of the imperative signal onwards) in the older, but not the young, group. Regression analyses revealed that for the older adults, modulation of LPMd-RM1 interactions early in the preparation period was associated with faster responses, suggesting that specifically timed modulation of these pathways may be a compensatory mechanism to offset, at least in part, slowing of motor responses. The results suggest a greater reliance on premotor regions during the preparation of simple motor actions with advancing age

Age-related differences in corticomotor excitability and inhibitory processes during a visuomotor RT task

This study tested the postulation that change in the ability to modulate corticospinal excitability and inhibitory processes underlie age-related differences in response preparation and generation during tasks requiring either rapid execution of a motor action or actively withholding that same action. Younger (n = 13, mean age = 26.0 years) and older adults (n = 13, mean age = 65.5 years) performed an RT task in which a warning signal (WS) was followed by an imperative signal (IS) to which participants were required to respond with a rapid flexion of the right thumb (go condition) or withhold their response (no-go condition). We explored the neural correlates of response preparation, generation, and inhibition using single- and paired-pulse TMS, which was administered at various times between WS and IS (response preparation phase) and between IS and onset of response-related muscle activity in the right thumb (response generation phase). Both groups exhibited increases in motor-evoked potential amplitudes (relative to WS onset) during response generation; however, this increase began earlier and was more pronounced for the younger adults in the go condition. Moreover, younger adults showed a general decrease in short-interval intracortical inhibition during response preparation in both the go and no-go conditions, which was not observed in older adults. Importantly, correlation analysis suggested that for older adults the task-related increases of corticospinal excitability and intracortical inhibition were associated with faster RT. We propose that the declined ability to functionally modulate corticospinal activity with advancing age may underlie response slowing in older adults

Bilateral intracortical inhibition during unilateral motor preparation and sequence learning

Motor sequence learning gradually quickens reaction time, suggesting that sequence learning alters motor preparation processes. Interestingly, evidence has shown that preparing sequence movements decreases short intracortical inhibition (SICI) in the contralateral motor cortex (M1), but also that sequence learning alters motor preparation processes in both the contralateral and ipsilateral M1s. Therefore, one possibility is that sequence learning alters the SICI decreases occurring during motor preparation in bilateral M1s. To examine this, two novel hypotheses were tested: unilateral sequence preparation would decrease SICI in bilateral M1s, and sequence learning would alter such bilateral SICI responses. Paired-pulse transcranial magnetic stimulation was delivered over the contralateral and ipsilateral M1s to assess SICI in an index finger muscle during the preparation of sequences initiated by either the right index or little finger. In the absence of sequence learning, SICI decreased in both the contralateral and ipsilateral M1s during the preparation of sequences initiated by the right index finger, suggesting that SICI decreases in bilateral M1s during unilateral motor preparation. As sequence learning progressed, SICI decreased in the contralateral M1 whilst it increased in the ipsilateral M1. Moreover, these bilateral SICI responses were observed at the onset of motor preparation, suggesting that sequence learning altered baseline SICI levels rather than the SICI decreases occurring during motor preparation per se. Altogether, these results suggest that SICI responses in bilateral M1s reflect two motor processes: an acute decrease of inhibition during motor preparation, and a cooperative but bidirectional shift of baseline inhibition levels as sequence learning progresses

Data-driven selection of conference speakers based on scientific impact to achieve gender parity

A lack of diversity limits progression of science. Thus, there is an urgent demand in science and the wider community for approaches that increase diversity, including gender diversity. We developed a novel, data-driven approach to conference speaker selection that identifies potential speakers based on scientific impact metrics that are frequently used by researchers, hiring committees, and funding bodies, to convincingly demonstrate parity in the quality of peer-reviewed science between men and women. The approach enables high quality conference programs without gender disparity, as well as generating a positive spiral for increased diversity more broadly in STEM

To be or not to be? What molecules say about Runcina brenkoae Thompson, 1980 (Gastropoda: Heterobranchia: Runcinida)

Runcinids are poorly known minute marine slugs inhabiting intertidal and shallow subtidal rocky shores. Among the European species, Runcina brenkoae, described from the Adriatic Sea in the Mediterranean, has been described to display chromatic variability, placing in question the true identity and geographic distribution of the species. In this paper we investigate the taxonomic status of R. brenkoae based on specimens from the central and western Mediterranean Sea and the southern Iberian coastline of Portugal and Spain, following an integrative approach combining multi-locus molecular phylogenetics based on the mitochondrial markers cytochrome c oxidase subunit I and 16S rRNA and the nuclear gene histone H3, together with the study of morpho-anatomical characters investigated by scanning electron microscopy. To aid in species delimitation, the Automatic Barcode Gap Discovery and Bayesian Poisson tree process methods were employed. Our results indicate the existence of a complex of three species previously identified as R. brenkoae, namely two new species here described (R. marcosi n. sp. and R. lusitanica n. sp.) and R. brenkoae proper

Noninvasive brain stimulation can elucidate and interact with the mechanisms underlying motor learning and retention: Implications for rehabilitation

Seminal work in animals indicates that learning a motor task results in long-term potentiation (LTP) in primary motor cortex (M1) and a subsequent occlusion of LTP induction (Rioult-Pedotti et al. J Neurophysiol 98: 3688-3695, 2007). Using various forms of noninvasive brain stimulation in conjunction with a motor learning paradigm, Cantarero et al. (J Neurosci 33: 12862-12869, 2013) recently provided novel evidence to support the hypothesis that retention of motor skill is contingent upon this postlearning occlusion

Functional role of left PMd and left M1 during preparation and execution of left hand movements in older adults

A disruptive transcranial magnetic stimulation (TMS) approach was used to determine whether the increased frontal activation and reduced hemispheric laterality brain activation patterns observed in older adults during motor tasks play a functional role. Young and older adults abducted their left index finger as soon as possible after a visual imperative signal presented 500 ms after a warning signal. TMS was applied to the dorsal premotor (PMd) or primary motor (M1) cortex in the left or right hemisphere at seven times during response preparation and execution. Both groups exhibited faster reaction times in their left hand after stimulation of the left PMd (i.e., ipsilateral to the responding hand) relative to trials with no TMS, indicating a functional role of the left PMd in the regulation of impulse control. This result also suggests that the function of the left PMd appears to be unaffected by the healthy aging process. Right M1 TMS resulted in a response time delay in both groups. Only for older adults did left M1 stimulation delay responses, suggesting the involvement of ipsilateral motor pathways in the preparation of motor actions in older adults

The contribution of visual feedback to visuomotor adaptation: How much and when?

We investigated the role of visual feedback in adapting to novel visuomotor environments. Participants produced isometric elbow torques to move a cursor towards visual targets. Following trials with no rotation, participants adapted to a 60 degrees rotation of the visual feedback before returning to the non-rotated condition. Participants received continuous visual feedback (CF) of cursor position during task execution or post-trial visual feedback (PF). With training, reductions of the angular deviations of the cursor path occurred to a similar extent and at a similar rate for CF and PF groups. However, upon re-exposure to the non-rotated environment only CF participants exhibited post-training aftereffects, manifested as increased angular deviation of the cursor path, with respect to the pre-rotation trials. These aftereffects occurred despite colour cues permitting identification of the change in environment. The results show that concurrent feedback permits automatic recalibration of the visuomotor mapping while post-trial feedback permits performance improvement via a cognitive strategy. (C) 2008 Elsevier B.V. All rights reserved

Slow and steady is not as easy as it sounds: Interlimb coordination at slow speed is associated with elevated attentional demand especially in older adults

The present study investigated age-related changes in the attentional demands associated with interlimb coordination involving upper and lower limbs performed at three different movement frequencies. Younger and older adults performed rhythmical, 180° out-of-phase flexion–extension movements of the knee and elbow with either ipsilateral (right arm, right leg) or contralateral (right arm, left leg) limbs at 20, 60, and 100 % of each individual’s maximum movement frequency. A concurrent vocal reaction time task (dual task) was used to assess attentional load. There were two major findings: (1) The attentional cost associated with undertaking the required coordination patterns was greatest at the slowest movement frequency, and this additional attentional load was most pronounced for older adults; (2) the manipulation of movement frequency had a distinct effect on the coordination performance: moving at the fastest frequency degraded the accuracy and stability of coordination, while moving at the slowest movement frequency led to increased temporal variability, particularly in older adults. Coordination performance at slowest movement frequency required the greatest cognitive demand in older adults relative to other movement frequencies, suggesting that going ‘slow and steady’ is not necessarily less attentionally demanding for older adults