Experimental Brain Research最新文献

We have shown that single-pulse transcranial magnetic stimulation (TMS) of the dorsolateral prefrontal cortex (dlPFC) inhibits muscle sympathetic nerve activity. However, this was likely due to arousal caused by the TMS pulses themselves, rather than altering the underlying neuronal circuitry. In extension, we have aimed to explore the effects of single-pulse TMS on skin sympathetic nerve activity (SSNA), which is more sensitive to arousal. It was hypothesised that TMS-evoked arousal would increase SSNA but would not generate de novo bursts from the dlPFC. Microneurographic recordings were taken from the right common peroneal nerve in 10 participants. TMS pulses were then delivered to the ipsilateral dlPFC at resting motor threshold (MT) of the finger, at stimulator output intensities 20% and 10% below MT, and at 110% and 120% of MT. The MT and 110% of MT intensities were also used in stimulating the right motor cortex and shoulder. Reductions in SSNA from baseline were seen at almost all intensities, and these mostly did not differ between intensities or sites despite the appearance of SSNA bursts after each pulse. This suggests that TMS is simply generating an arousal response, leading to initial excitation of SSNA followed by a period of sympathoinhibition.

A transient increase in cerebral blood flow (CBF) via exercise or hypercapnia has-in part-been linked to an executive function (EF) benefit. It is, however, unclear whether a transient reduction in CBF negatively impacts EF. In the present study, healthy young adults (n = 24) completed separate 3-h interventions involving - 12° head-down tilt (HDT) and a control (0°) supine posture. The HDT protocol was used because it induces a cephalad fluid shift that safely and reliably decreases CBF. To estimate CBF, transcranial Doppler ultrasound measured middle cerebral artery velocity (MCAv) at discrete timepoints (i.e., baseline, concurrent with the intervention and recovery) and the Stroop colour-naming task completed at baseline, 30-min intervals throughout the intervention and a recovery timepoint, assessed inhibitory control-based changes in EF. As expected, a time-dependent decrease in MCAv (8%) was observed in the HDT but not the control intervention; however, frequentist and Bayesian statistics demonstrated that Stroop performance metrics were not associated with the MCAv change (ps > 0.12). Instead, time-dependent deficits in Stroop task performance were associated with increased ratings of mental fatigue-a result observed across HDT and control interventions. Accordingly, a reduction in MCAv during a 3-h HDT intervention did not impact an inhibitory control measure of EF and our findings demonstrates neurocognitive resilience during a short-term reduction in CBF.

The sense of agency (SoA)-the experience of being in control of one's own actions and outcomes-is a fundamental aspect of daily life. Prior research shows that SoA can be disturbed when actions are externally instructed rather than voluntarily initiated; however, the role of the instructing agent specifically in shaping this effect remains underexplored. As artificial agents (e.g., online chatbots, virtual avatars) become increasingly embedded in everyday interactions, their potential to influence human action raises important questions about the experience of agency. Across three studies, we investigate how action instructions delivered by a human or an artificial agent (in the form of an on-screen embodied chatbot) influence both implicit (temporal binding) and explicit (self-reported control) measures of agency. The results of Study 1 (implicit) showed that binding was strongest in the free choice condition wherein participants' actions were of their own volition compared to actions conducted under external instruction. Notably, binding was significantly reduced when actions were directed by a chatbot compared to the free choice condition. Similarly, the results of Study 2 (explicit) showed that self-reported control ratings were the highest in the free choice condition and decreased significantly when comparing the free choice condition with both instruction conditions. After conducting a third follow-up study that integrates both implicit and explicit methods, we were able to replicate the findings of Study 1 and 2. These results highlight a distinction in the experience of agency when responding to human- versus technology-driven instructions.

Lifting everyday objects destabilizes the body and requires generation of anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain balance. Aging is associated with reduced efficiency of APA generation and greater reliance on CPAs. The role of Mild Cognitive Impairment (MCI) in postural control during lifting remains unclear. We investigated how age and MCI influence postural adjustments during a standing bimanual lifting task. 13 healthy older adults (OAH), 15 older adults with MCI (OAMCI), and 12 young adults (YAH) performed 35 trials of bimanual lifting of light and heavy loads in standing. Surface electromyography was collected bilaterally from trunk and lower limb muscles, and EMG integrals were calculated during the APA and CPA phases. Center of pressure (COP) displacements were derived from force platform data. YAH generated significantly greater APAs in muscle activity and exhibited larger anticipatory COP responses than both older groups during the heavy-to-light transition (p < .05). They also produced larger compensatory COP responses across transitions. OAMCI showed reduced TA activation during the light-to-heavy transition but demonstrated exaggerated APAs in posterior and lateral muscles during the heavy-to-light transition compared with OAH (p < .05). Change-point analysis indicated faster adaptation to load changes in YAH than in both older groups. Aging and MCI differentially affect the ability to regulate APAs and CPAs during lifting. Young adults demonstrated efficient scaling and rapid adaptation of postural control, whereas older adults showed reduced anticipatory efficiency and slower adjustment. Individuals with MCI exhibited exaggerated yet less targeted APA patterns, suggesting impaired strategy selection.

Avian pecking behavior in birds, analogous to reach-to-grasp in primates, is accompanied by unstable vision due to the co-location of the eyes and bills on the head. Fixation in birds, a brief pause during pecking, enables them to stabilize their visual input to plan their further movements. Several bird species have two high-acuity retinal regions, the area dorsalis and the fovea centralis, which receive input from frontal and lateral visual fields, respectively. However, the contributions of these regions to natural pecking during fixation, especially temporal dynamics and head posture involved in accommodation, remain poorly understood. We assessed the effects of visual-field-specific occlusion on the fixation behavior of pigeons, provided with three types of eye caps: frontal occlusion, lateral occlusion, and a no-occlusion control. Using video tracking methods, we analyzed the visual distance toward the target, fixation duration, head depression angle, and the covariation between visual distance and duration. Frontal occlusion markedly prolonged fixation duration and increased the head depression angle, whereas visual distance remained unaffected across conditions. Furthermore, the covariation between visual distance and fixation duration under control condition was abolished under frontal occlusion. These results suggest that the role of frontal vision involves the area dorsalis in temporal and postural compensation for accommodation during fixation of pecking.

Everyday experience suggests that handheld containers convey auditory and haptic information about their contents. The primary objective of this study was to examine how these two sources of information interact. Across three experiments, participants estimated the number of beads in cardboard boxes under three sensory conditions: haptics-only, auditory-only, and auditory-haptic. We hypothesized that the auditory-haptic condition would yield more accurate and precise estimates. A secondary objective was to assess the effects of time and manipulation constraints. In Experiment 1, participants were limited to 5 s of exploration using a standardized movement; Experiment 2 removed the time constraint, and Experiment 3 additionally removed the movement constraint. Results indicated that participants could reliably estimate the number of items under all conditions but provided little evidence for multisensory integration. When both constraints were removed, the haptic-only condition produced significantly more accurate estimates. These findings suggest that manipulation constraints influence enumeration performance and that haptic cues can support accurate judgments when exploration is unconstrained.

Combined examination of mental workload and biomechanics during dual-task walking in individuals with lower-limb loss is limited to fixed, but not self-modulated walking pace, for which the latter enables dynamic cognitive-motor behavior as typically engaged during community ambulation. By assessing electroencephalography (EEG) (theta, low/high-alpha power) and biomechanics (gait speed, double limb support, stride width), the cerebral cortical activity underlying mental workload and walking mechanics were examined when individuals with and without lower-limb loss executed a cognitive task (assessed via response time and accuracy) under variable demand (seated and walking). Both populations maintained walking mechanics (unchanged gait speed, double limb support, stride width) during dual-task walking across demand and exhibited similarly elevated neurocognitive engagement (e.g., attention, action monitoring) indicated by similar theta power increase and low/high-alpha power decrease when facing greater demand. However, injured individuals exhibited relative performance decrement (degraded response time/accuracy), which suggests attenuated cognitive-motor efficiency relative to uninjured (i.e., similar cortical activity across groups with degraded performance). Moreover, while uninjured individuals during dual-task walking could robustly engage neurocognitive processes to maintain walking mechanics and successfully attend to the concurrent cognitive task, those with lower-limb loss did not exhibit such a robust recruitment (i.e., unchanged frontal/temporal high-alpha power). Such alterations in individuals with lower-limb loss leads to maintenance of walking at the cost of a concurrent task. The present work informs rehabilitation practice and reveals specific cognitive-motor outcomes for individuals with lower-limb loss in an enhanced ecological context.

Pitching is an essential skill in baseball, requiring precise and well-coordinated neural control. However, elucidating its underlying neural mechanisms remains challenging because of the methodological difficulties in assessing neural activity during dynamic movement. Motor imagery (MI) provides a potential approach for investigating neural control in pitching, as MI of basic movements activates neural processes similar to those during actual movement. This study examined how MI of pitching, with and without visual guidance, modulates corticospinal excitability in muscles involved in pitching. Electromyographic activity was recorded from the flexor carpi radialis (FCR), extensor carpi radialis, first dorsal interosseous, and abductor pollicis brevis (APB) muscles. Corticospinal excitability was evaluated by motor-evoked potential (MEP) amplitudes, elicited by transcranial magnetic stimulation to the primary motor cortex. MEPs were measured during kinesthetic MI across five sports skills, using only MI in Experiment 1 and using MI with a model video (vMI) in Experiment 2. Results showed that both types of baseball-MI significantly facilitated corticospinal excitability in APB, and baseball-vMI significantly facilitated corticospinal excitability in FCR, but not in other recorded muscles compared with those at rest. These results likely reflect the relative contribution and functional role of each muscle and fine motor control in actual pitching. The facilitation in APB was specific to baseball-MI/vMI, and this specificity is further supported by the findings that each sport's MI/vMI selectively facilitated corticospinal excitability in the muscle involved in the imagined movements. These findings provide foundational knowledge and a methodology for investigating the modulation of corticospinal excitability during pitching.

Hand dominance influences motor control, yet the nature of asymmetries in reach-to-grasp coordination remains unclear. We used an immersive, haptic-free virtual environment to examine how hand dominance, object size, and distance shape kinematics and muscle activity during reach-to-grasp actions. Twelve right-handed participants performed unilateral movements with both hands toward virtual objects varying in size and distance. Kinematic and electromyographic data were collected from transport- and grasp-related muscles. A 2 (Hand: dominant, non-dominant) × 3 (Distance: near, middle, far) × 3 (Size: small, medium, large) repeated-measures ANOVA evaluated effects on movement parameters. Transport with the non-dominant hand showed higher peak velocities and accelerations and greater variability in 3-D position compared with the dominant hand. These differences were accompanied by increased triceps brachii activation during late transport, likely reflecting compensatory deceleration and stabilization before grasp. In contrast, grasp kinematics and grasp-related electromyographic activity did not differ significantly between hands. Task parameters modulated both transport and grasp, but object distance more strongly influenced transport, whereas object size more consistently affected grasp. Reach-to-grasp coordination in virtual reality revealed functional specialization between the hands, with asymmetries evident in transport but not grasp. These findings support models proposing a proximal-distal division of motor function between limbs. The results also demonstrate the utility of haptic-free VR as a methodological tool for investigating and potentially training limb-specific motor strategies in healthy individuals.

The aim of this study was to examine the organization of ball-catching movements with different biomechanical structures, which are among the profile elements in rhythmic gymnastics, based on common synergies. An additional goal was to identify specific synergies presumably formed during the performing of movements with increased coordinative complexity. Synergy parameters were derived from simultaneously recorded electromyographic (EMG) data from 16 muscles and joint angle kinematics; factor analysis and principal component analysis were applied. It was found that at the kinematic level, participants demonstrated similar motor control strategies for catching the ball. Interjoint coordination was structured into two modules, independent of the motor task's complexity. The specificity of kinematic modules manifested in a shift of the main peak of interjoint interaction synchronization, driven by the subjective perception of the ball contact moment. At the muscular level, up to five muscle modules were identified, two of which were consistently present across different ball-catching movements. Their function is associated with generating active motions of the upper limb segments and stabilizing the shoulder girdle. The component composition of muscle synergies is largely determined by the movements' biomechanical structure and the presence of a common subtask within them.