Split-Belt Training but Not Cerebellar Anodal tDCS Improves Stability Control and Reduces Risk of Fall in Patients with Multiple Sclerosis

The objective of this study was to examine the therapeutic potential of multiple sessions of training on a split-belt treadmill (SBT) combined with cerebellar anodal transcranial direct current stimulation (tDCS) on gait and balance in People with Multiple Sclerosis (PwMS). Twenty-two PwMS received six sessions of anodal (PwMSreal, n = 12) or sham (PwMSsham, n = 10) tDCS to the cerebellum prior to performing the locomotor adaptation task on the SBT. To evaluate the effect of the intervention, functional gait assessment (FGA) scores and distance walked in 2 min (2MWT) were measured at the baseline (T0), day 6 (T5), and at the 4-week follow up (T6). Locomotor performance and changes of motor outcomes were similar in PwMSreal and PwMSsham independently from tDCS mode applied to the cerebellum (anodal vs. sham, on FGA, p = 0.23; and 2MWT, p = 0.49). When the data were pooled across the groups to investigate the effects of multiple sessions of SBT training alone, significant improvement of gait and balance was found on T5 and T6, respectively, relative to baseline (FGA, p < 0.001 for both time points). The FGA change at T6 was significantly higher than at T5 (p = 0.01) underlining a long-lasting improvement. An improvement of the distance walked during the 2MWT was also observed on T5 and T6 relative to T0 (p = 0.002). Multiple sessions of SBT training resulted in a lasting improvement of gait stability and endurance, thus potentially reducing the risk of fall as measured by FGA and 2MWT. Application of cerebellar tDCS during SBT walking had no additional effect on locomotor outcomes.

Evidence that endpoint feedback facilitates intermanual transfer of visuomotor force learning by a cognitive strategy

Humans continuously adapt their movement to a novel environment by recalibrating their sensorimotor system. Recent evidence, however, shows that explicit planning to compensate for external changes, i.e. a cognitive strategy, can also aid performance. If such a strategy is indeed planned in external space, it should improve performance in an effector independent manner. We tested this hypothesis by examining whether promoting a cognitive strategy during a visual-force adaptation task performed in one hand can facilitate learning for the opposite hand. Participants rapidly adjusted the height of visual bar on screen to a target level by isometrically exerting force on a handle using their right hand. Visuomotor gain increased during the task and participants learned the increased gain. Visual feedback was continuously provided for one group, while for another group only the endpoint of the force trajectory was presented. The latter has been reported to promote cognitive strategy use. We found that endpoint feedback produced stronger intermanual transfer of learning and slower response times than continuous feedback. In a separate experiment, we found evidence that the aftereffect is indeed reduced when only endpoint feedback is provided, a finding that has been consistently observed when cognitive strategies are used. The results suggest that intermanual transfer can be facilitated by a cognitive strategy. This indicates that the behavioral observation of intermanual transfer can be achieved either by forming an effector-independent motor representation, or by sharing an effector-independent cognitive strategy between the hands.

Impaired Sensorimotor Adaption in Schizophrenia in Comparison to Age-Matched and Elderly Controls

<b><i>Background:</i></b> The “cognitive dysmetria hypothesis” of schizophrenia proposes a disrupted communication between the cerebellum and cerebral cortex, resulting in sensorimotor and cognitive symptoms. Sensorimotor adaptation relies strongly on the function of the cerebellum. <b><i>Objectives:</i></b> This study investigated whether sensorimotor adaptation is reduced in schizophrenia compared with age-matched and elderly healthy controls. <b><i>Methods:</i></b> Twenty-nine stably treated patients with schizophrenia, 30 age-matched, and 30 elderly controls were tested in three motor adaptation tasks in which visual movement feedback was unexpectedly altered. In the “rotation adaptation task” the perturbation consisted of a rotation (30° clockwise), in the “gain adaptation task” the extent of the movement feedback was reduced (by a factor of 0.7) and in the “vertical reversal task,” up- and downward pen movements were reversed by 180°. <b><i>Results:</i></b> Patients with schizophrenia adapted to the perturbations, but their movement times and errors were substantially larger than controls. Unexpectedly, the magnitude of adaptation was significantly smaller in schizophrenia than elderly participants. The impairment already occurred during the first adaptation trials, pointing to a decline in explicit strategy use. Additionally, post-adaptation aftereffects provided strong evidence for impaired implicit adaptation learning. Both negative and positive schizophrenia symptom severities were correlated with indices of the amount of adaptation and its aftereffects. <b><i>Conclusions:</i></b> Both explicit and implicit components of sensorimotor adaptation learning were reduced in patients with schizophrenia, adding to the evidence for a role of the cerebellum in the pathophysiology of schizophrenia. Elderly individuals outperformed schizophrenia patients in the adaptation learning tasks.

Early visual processing as a marker of disease, not vulnerability: Event-related potential (ERP) evidence from 22q11.2 deletion syndrome, a population at high risk for schizophrenia

We investigated visual processing in 22q11.2 deletion syndrome (22q11.2DS), a condition characterized by an increased risk for schizophrenia. Visual processing differences have been described in schizophrenia but remain understudied early in the disease course. Electrophysiology was recorded during a visual adaptation task with different interstimulus intervals to investigate visual processing and adaptation in 22q11.2DS (with (22q+) and without (22q-) psychotic symptoms), compared to control and idiopathic schizophrenia groups. Analyses focused on early windows of visual processing. While increased amplitudes were observed in 22q11.2DS in an earlier time window (90-140 ms), decreased responses were seen later (165-205 ms) in schizophrenia and 22q+. 22q11.2DS, and particularly 22q-, presented increased adaptation effects. We argue that while amplitude and adaptation in the earlier time window may reflect specific neurogenetic aspects associated with a deletion in chromosome 22, amplitude in the later window may be a marker of the presence of psychosis and/or of its chronicity/severity.

Visuomotor Adaptation Brain Changes During a Spaceflight Analog With Elevated Carbon Dioxide (CO2): A Pilot Study

Astronauts on board the International Space Station (ISS) must adapt to several environmental challenges including microgravity, elevated carbon dioxide (CO2), and isolation while performing highly controlled movements with complex equipment. Head down tilt bed rest (HDBR) is an analog used to study spaceflight factors including body unloading and headward fluid shifts. We recently reported how HDBR with elevated CO2 (HDBR+CO2) affects visuomotor adaptation. Here we expand upon this work and examine the effects of HDBR+CO2 on brain activity during visuomotor adaptation. Eleven participants (34 ± 8 years) completed six functional MRI (fMRI) sessions pre-, during, and post-HDBR+CO2. During fMRI, participants completed a visuomotor adaptation task, divided into baseline, early, late and de-adaptation. Additionally, we compare brain activity between this NASA campaign (30-day HDBR+CO2) and a different campaign with a separate set of participants (60-day HDBR with normal atmospheric CO2 levels, n = 8; 34.25 ± 7.9 years) to characterize the specific effects of CO2. Participants were included by convenience. During early adaptation across the HDBR+CO2 intervention, participants showed decreasing activation in temporal and subcortical brain regions, followed by post- HDBR+CO2 recovery. During late adaptation, participants showed increasing activation in the right fusiform gyrus and right caudate nucleus during HDBR+CO2; this activation normalized to baseline levels after bed rest. There were no correlations between brain changes and adaptation performance changes from pre- to post HDBR+CO2. Also, there were no statistically significant differences between the HDBR+CO2 group and the HDBR controls, suggesting that changes in brain activity were due primarily to bed rest rather than elevated CO2. Five HDBR+CO2 participants presented with optic disc edema, a sign of Spaceflight Associated Neuro-ocular Syndrome (SANS). An exploratory analysis of HDBR+CO2 participants with and without signs of SANS revealed no group differences in brain activity during any phase of the adaptation task. Overall, these findings have implications for spaceflight missions and training, as ISS missions require individuals to adapt to altered sensory inputs over long periods in space. Further, this is the first study to verify the HDBR and elevated CO2 effects on the neural correlates of visuomotor adaptation.

Experience of After-Effect of Memory Update Reduces Sensitivity to Errors During Sensory-Motor Adaptation Task

Motor learning is the process of updating motor commands in response to a trajectory error induced by a perturbation to the body or vision. The brain has a great capability to accelerate learning by increasing the sensitivity of the memory update to the perceived trajectory errors. Conventional theory suggests that the statistics of perturbations or the statistics of the experienced errors induced by the external perturbations determine the learning speeds. However, the potential effect of another type of error perception, a self-generated error as a result of motor command updates (i.e., an aftereffect), on the learning speeds has not been examined yet. In this study, we dissociated the two kinds of errors by controlling the perception of the aftereffect using a channel-force environment. One group experienced errors due to the aftereffect of the learning process, while the other did not. We found that the participants who perceived the aftereffect of the memory updates exhibited a significant decrease in error-sensitivity, whereas the participants who did not perceive the aftereffect did not show an increase or decrease in error-sensitivity. This suggests that the perception of the aftereffect of learning attenuated updating the motor commands from the perceived errors. Thus, both self-generated and externally induced errors may modulate learning speeds.

Frontal increase of movement-related beta modulation is enhanced by visuo-motor learning

Recently we found that enhancements of movement-related beta (13.5–25 Hz) modulation (measured as event-related desynchronization peak to synchronization peak) during a simple reaching test (mov) occur over frontal and left sensorimotor regions after extended practice in a visuo-motor adaptation task (ROT) but not after similar duration practice in a visual learning task. Here we verify whether those enhancements are also trigged by motor practice alone or the additional learning component inherent in the visuo-motor adaptation task is needed. In healthy young subjects, beta modulation during mov increased over frontal and contralateral sensorimotor areas after three-hour practice of either ROT or reaching movements without visuo-motor adaptation (MOT). However, while the increase over the left area was similar after the two tasks, the frontal increase was greater after ROT practice. These findings confirm previous reports that extensive practice leaves local traces in beta power both at rest and during the subsequent execution of a motor test. They further suggest that, since they occur after motor tasks with (ROT) and without learning (MOT), these traces likely express the cost of processes necessary both for usage of these areas and for the engagement of long-term potentiation mechanisms necessary for creating new internal models.

Speech-specific perceptual adaptation deficits in children and adults with dyslexia

According to several influential theoretical frameworks, phonological deficits in dyslexia result from reduced sensitivity to acoustic cues that are essential for the development of robust phonemic representations. Some accounts suggest that these deficits arise from impairments in rapid auditory adaptation processes that are either speech-specific or domain-general. Here, we examined the specificity of auditory adaptation deficits in dyslexia using a non-linguistic tone anchoring (adaptation) task and a linguistic selective adaptation task in children and adults with and without dyslexia. Children and adults with dyslexia had elevated tone-frequency discrimination thresholds, but both groups benefitted from anchoring to repeated stimuli to the same extent as typical readers. Additionally, although both dyslexia groups had overall reduced accuracy for speech sound identification, only the child group had reduced categorical perception for speech. Across both age groups, individuals with dyslexia had reduced perceptual adaptation to speech. These results highlight broad auditory perceptual deficits across development in individuals with dyslexia for both linguistic and non-linguistic domains, but speech-specific adaptation deficits. Finally, mediation models in children and adults revealed that the causal pathways from basic perception and adaptation to phonological awareness through speech categorization were not significant. Thus, rather than having causal effects, perceptual deficits may co-occur with the phonological deficits in dyslexia across development.