Experimental Brain Research最新文献

Hand(s)-tapping tasks have been extensively studied in order to characterize the features of sensorimotor synchronization (SMS). These tasks frequently require participants to synchronize their tapping pace to an external, metronome-like sound. The impact of ageing on SMS abilities remains mainly unexplored. Thus, we conducted a series of hand tapping tasks on 15 young adults (YA) and 15 older adults (OA). The tasks included tapping with the dominant hand only (D), with the non-dominant hand only (ND), with both hands simultaneously (SIM), and alternating between the hands (ALT). Participants in each task performed a synchronization-continuation task, in which they had to tap for one minute according to an external sound set at their spontaneous motor tempo (separately identified), and then, after the sound stopped, continue tapping at the same tempo for another minute. Results indicated a set of preserved and degraded tapping behaviors in OA compared to YA. The ALT task produced the most deteriorated tapping performance, followed by the ND task; the other two tasks revealed no difference between the groups. These findings shed more light on how SMS declines across the lifespan and provide some preliminary but important information that may guide rehabilitation and diagnostic procedures.

When we touch ourselves, the pressure appears weaker compared to when someone else touches us, an effect known as sensory attenuation. Sensory attenuation is spatially tuned and does only occur if the positions of the touching and the touched body-party spatially coincide. Here, we ask about the contribution of visual or proprioceptive signals to determine self-touch. By using a 3D arm model in a virtual reality environment, we dissociated the visual from the proprioceptive arm signal. When a virtual arm was visible indicating self-touch, we found that sensory attenuation generalized across different locations. When no virtual arm was visible, we found sensory attenuation to be strongest when subjects pointed to the position where they felt their arm to be located. We conclude that the spatial tuning of tactile attenuation depends on which signal determines the occurrence of self-touch. When observers can see their hand, the visual signal dominates the proprioceptive determining self-touch in a single visual snapshot. When only the proprioceptive signal is available, the positions of the touching and the touched body-part must be separately estimated and subsequently compared if they overlap in anatomical space.

This study explores the role of task constraints over muscle synergies expression in the context of upper limb motor impairment after stroke. We recruited nine chronic stroke survivors with upper limb impairments and fifteen healthy controls, who performed a series of tasks designed to evoke muscle synergies through various spatial explorations. These tasks included an isometric force task, a dynamic reaching task, the clinical Fugl-Meyer (FM) assessment, and a pinch task. Electromyographic data from 16 upper limb muscles were collected during each task, alongside intermuscular coherence (IMC) measurements during the pinch task to assess neuromuscular connectivity. The findings confirm that motor impairment is inversely related to the diversity of muscle synergies, with fewer synergies and more stereotypical synergy structures observed post-stroke. The study further reveals that the nature of motor tasks significantly affects the number of identifiable muscle synergies, with less constrained tasks revealing a broader array of synergies. These findings highlight the importance of carefully selecting motor tasks in the context of clinical research and assessments to understand a patient's motor impairment, thus aiding in developing tailored rehabilitation strategies.

The aim of this study was to assess if ischaemic preconditioning (IPC) can reduce pain perception and enhance corticospinal excitability during voluntary contractions. In a randomised, within-subject design, healthy participants took part in three experimental visits after a familiarisation session. Measures of pressure pain threshold (PPT), maximum voluntary isometric force, voluntary activation, resting twitch force, corticospinal excitability and corticospinal inhibition were performed before and ≥10 min after either, unilateral IPC on the right leg (3 × 5 min); a sham protocol (3 × 1 min); or a control (no occlusion). Pain perception was then assessed in response to a hypertonic saline injection into the vastus lateralis muscle. In the right (occluded) leg, PPT was 10% greater after IPC compared to sham (P = 0.004). PPTs were also 9.5% greater in the contralateral leg for IPC compared to sham (P = 0.031). Maximum voluntary force, voluntary activation and resting twitch force were not different between conditions (all P ≥ 0.133). Measures of corticospinal excitability and inhibition also revealed no significant differences between conditions (all P ≥ 0.240). Hypertonic saline evoked pain revealed no difference in reported intensity or duration between conditions (P ≥ 0.082). IPC can reduce pain sensitivity in local and remote areas but does not subsequently impact neurophysiological measures of excitability or inhibition.

This study investigated the relationship between eye movement parameters and cognitive function in patients with mild to moderate Alzheimer's disease (AD). A total of 80 patients with AD (mild and moderate) and 34 normal controls (NC) participated. Neuropsychological assessments were conducted using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA), while eye movements were recorded using eye-tracking technology. Comparisons of neuropsychological scores and eye movement parameters were made across the groups, and partial correlation analysis was performed to examine associations between eye movement metrics and specific cognitive domains. No significant differences were found among the groups in pursuit and fixation tasks. However, in pro-saccade tasks, patients in the moderate AD group exhibited significantly lower accuracy and longer latency compared to those in the mild AD and NC groups. Similarly, in anti-saccade tasks, the moderate AD group showed significantly lower accuracy and error correction rates compared to the other groups. Partial correlation analysis revealed that overall cognitive function was positively associated with the accuracy of pro-saccade and anti-saccade tasks, as well as the error correction rate of anti-saccade tasks, but negatively associated with pro-saccade latency. Further, orientation was negatively correlated with saccade latency and positively correlated with saccade accuracy, while visuospatial skills were positively associated with the accuracy of both saccade and anti-saccade tasks. A positive correlation was also observed between word fluency and both saccade accuracy and error correction rate. These findings indicate that eye movement parameters, particularly those related to saccade and anti-saccade tasks, are associated with various cognitive domains in mild to moderate AD patients. Eye-tracking technology may provide a convenient and non-invasive tool for assessing cognitive function and aiding in the diagnosis and evaluation of AD.

Working memory (WM) reflects the transient maintenance of information in the absence of external input, which can be attained via multiple senses separately or simultaneously. Pertaining to WM, the prevailing literature suggests the dominance of vision over other sensory systems. However, this imbalance may be stemming from challenges in finding comparable stimuli across modalities. Here, we addressed this problem by using a balanced multisensory retro-cue WM design, which employed combinations of auditory (ripple sounds) and visuospatial (Gabor patches) patterns, adjusted relative to each participant's discrimination ability. In three separate experiments, the participant was asked to determine whether the (retro-cued) auditory and/or visual items maintained in WM matched or mismatched the subsequent probe stimulus. In Experiment 1, all stimuli were audiovisual, and the probes were either fully mismatching, only partially mismatching, or fully matching the memorized item. Experiment 2 was otherwise the same as Experiment 1, but the probes were unimodal. In Experiment 3, the participant was cued to maintain only the auditory or visual aspect of an audiovisual item pair. In Experiments 1 and 3, the participant's matching performance was significantly more accurate for the auditory than visual attributes of probes. When the perceptual and task demands are bimodally equated, auditory attributes can be matched to multisensory items in WM at least as accurately as, if not more precisely than, their visual counterparts.

Understanding the complex activation patterns of brain regions during motor tasks is crucial. Integrated functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) offers advanced insights into how brain activity fluctuates with motor activities. This study explores neuronal activation patterns in the cerebral cortex during active, passive, and imagined wrist movements using these functional imaging techniques. Data were collected from 10 right-handed volunteers performing a motor task using fMRI and fNIRS. fMRI utilized a 3T scanner and a 20-channel head coil, while fNIRS recorded data with a 48-channel device at 765 nm and 855 nm. Analysis focused on key motor and sensory cortices using NIRS-SPM and SPM12, applying a significance threshold of p < 0.05 and a minimum cluster size of 10 voxels for group analysis. Super-threshold voxels were identified with FWE thresholding in SPM12. For activation map extraction we focused on the primary motor cortex, primary somatosensory cortex, somatosensory association cortex, premotor cortex, and supplementary motor cortex. Both fMRI and fNIRS detected activation in the primary motor cortex (M1). The primary somatosensory cortex was found to influence movement direction coding, with smaller activation sizes for upward movements. Combining fNIRS with fMRI provided clearer differentiation of brain activation patterns for wrist movements in various directions and conditions (p < 0.05). This study highlights variations in left motor cortex activity across different movement states. fNIRS proved effective in detecting brain function and showed strong correlation with fMRI results, suggesting it as a viable alternative for those unable to undergo fMRI.

Accurate control of force on the environment is mechanically necessary for many tasks involving the lower extremities. We investigated drifts in the horizontal (shear) active force produced by right-footed seated subjects and the effects of force matching by the other foot. Subjects generated constant shear force at 15% and 30% of maximal voluntary contraction (MVC) using one foot. Visual feedback of shear force magnitude was provided for the first 5s, then turned off for 30s. During the 30% MVC task, we observed parallel drops in active shear and vertical force magnitudes leading to consistent drifts in the resultant force magnitude, not in its direction. Force matching by the other foot resulted in significantly lower forces when feedback was available throughout the trial. No feedback was provided for the matching foot. When the matching foot began exerting force, the task foot experienced a notable drop in all force components, with a change in force direction only for the task foot. After this initial drop, the downward drift in the task foot stopped or reversed. Subjects were unaware of these drifts and errors. Our findings suggest that shear force production involves setting a referent coordinate vector, which shows drifts and matching errors, while its direction remains stable. Involvement of the matching foot appears to perturb the neural commands to the task foot, with minor differences observed between feet. The discrepancy between the consistent force drifts and lack of awareness of the drifts indicates a difference between force perception-to-act and perception-to-report.

Injury to one cerebral hemisphere can result in paresis of the contralesional hand and subsequent preference of the ipsilesional hand in daily activities. However, forced use therapy in humans can improve function of the contralesional paretic hand and increase its use in daily activities, although the ipsilesional hand may remain preferred for fine motor activities. Studies in monkeys have shown that minimal forced use of the contralesional hand, which was the preferred hand prior to brain injury, can produce remarkable recovery of function. Here we tested the hypothesis that long-term forced use of the contralesional hand during the post-lesion period can return it to preferred status. Four rhesus monkeys received tests of hand preference prior to surgical lesions of primary motor cortex, lateral premotor cortex and anterior parietal cortex (F2P2 lesion) contralateral to the preferred hand. Beginning two weeks after the lesion, forced use therapy involving contralateral hand reaches to acquire food targets occurred 3X weekly with at least 300 reaches/session until 24 weeks post-lesion. Despite initial paresis of the contralesional hand, its manipulation skill returned to near pre-lesion levels or higher and all four monkeys returned to a contralesional hand preference late in the post-lesion period. Favorable reorganization of spared cortical and subcortical neural networks may promote recovery of hand function and preference. These results have relevance for the use of extensive forced-use therapy in humans who experience unilateral periRolandic injury to potentially support better recovery of contralesional hand function.

In sensory perception, stochastic resonance (SR) refers to the application of noise to enhance information transfer, allowing for the sensing of lower-level stimuli. Previously, subjective-assessments identified SR in vestibular perceptual thresholds, assessed using a standard two alternative (i.e., binary), forced-choice task, when applying noisy Galvanic Vestibular Stimulation (nGVS). However, this required extensive testing of at least 100 binary trials to yield sufficiently precise thresholds at each of several nGVS amplitudes, leading to confounds of fatigue, sleepiness, learning, etc. stalling the study of vestibular SR. To mitigate this, we explore confidence reporting, which via a confidence signal detection (CSD) model may much more efficiently identify SR (i.e., with fewer trials), if SR exists in CSD thresholds. To test this, Y-translation thresholds were tested with 100 trials at each nGVS amplitude (0 or sham, 0.1, 0.2, 0.3 and 0.4 mA peak-to-peak). To objectively identify SR, we applied a machine learning classification algorithm trained on simulated datasets. We found significant evidence of SR exhibition using CSD thresholds (p = 0.0025), with six of 10 subjects classified as exhibiting SR. Next, we considered fewer trials, finding the false positive rate of SR identification to be better using CSD thresholds with as few as 50 trials, when compared to 100 binary trials. Applying the CSD model to our subject's data with a subset of their trials found similar classifications of SR exhibition as with 100 binary trials. We demonstrate CSD thresholds exhibit SR, proving a means of better and much more efficiently identifying SR.