Experimental Brain Research最新文献

Safe gait requires visually cued (VC) step adjustments for negotiating targets and obstacles. Effective step adjustments rely on good visuospatial processing. The posterior parietal cortex (PPC) is implicated in visuospatial processing, yet empirical evidence is limited for the PPC's role during gait in humans. Increased cortical control of gait is associated with higher gait variability, a marker of gait performance and fall risk among older adults. However, the cortical underpinnings of gait variability in visually complex environments are not well established. The primary aim of this preliminary study was to assess PPC activity during VC gait and VC gait with perturbations (VCP). A secondary aim was to determine how PPC activity relates to gait variability during VC and VCP gait. Twenty-one healthy young adults completed three treadmill gait conditions at preferred speed: non-cued (NC) gait, VC gait, where stepping targets were presented in a regular pattern, and VCP gait, where stepping target positions were pseudorandomly shifted. Functional near-infrared spectroscopy quantified relative changes in deoxygenated and oxygenated hemoglobin (ΔHbO₂) concentrations in the PPC. Inertial measurement units quantified gait variability. Moderate effects were observed for more positive ΔHbO₂ from NC to both VC and VCP gait, likely reflecting the increased visuospatial processing demands. Stride time variability was positively correlated with PPC ΔHbO₂ during VC gait, suggesting a potential role for the PPC in modulating temporal components of VC gait. Extending these findings to older adults will help to elucidate the PPC's role in gait adaptability and fall risk with aging.

Evidence has shown a wide range of changes in pain perception in posttraumatic stress disorder (PTSD). The present study aimed to explore changes in thermal pain threshold in both sexes of rats exposed to electrical footshocks in different periods after fear conditioning. Fear conditioning (PTSD-like model) was induced by three footshocks (0.8 mA, 3 s) paired with sounds (75 dB, 3 s). Extinction was performed using twenty sounds (75 dB, 3 s) with no footshocks, 1 h after footshocks. Freezing and pain threshold were measured 2 h, 2 days, 7 days, or 30 days after PTSD or extinction (there was not any recall session). The results showed freezing behavior showed a downward trend over time in males, while an upward trend over time in females. Extinction slightly decreased freezing behavior in males, while significantly decreased it in females. Pain threshold was increased in male PTSD rats, while after 30days, there was no change in pain perception. In females, pain threshold was restored in both PTSD-7d and - 30d groups. Extinction decreased pain threshold in males, with stronger effect in females. BDNF was decreased and GSK-3beta was increased in male PTSD rats, except PTSD-30d only for BDNF. In females, BDNF level was restored in both PTSD-7d and - 30d, and also, increased in PTSD-2d group, while GSK-3beta was increased. In conclusion, significant sex differences were observed in freezing behavior, pain threshold, and BDNF. Notably, it seems that GSK-3beta may be involved in freezing and pain perception changes only in females exposed to extinction session.

Previous research suggests exercise improves spatial navigation abilities, though the effects of different exercise intensities on this cognitive function have not been explored. The current study assessed the influence of moderate-intensity and high-intensity acute exercise on spatial learning and memory, focusing on the acquisition of survey and route knowledge in young adults. Thirty-two participants (22.6 ± 1.7 y) were randomly assigned to one of three groups: (1) no-exercise control (n = 10); (2) moderate-intensity continuous training (MICT; 30 min at 75% maximal heart rate) (n = 12); (3) sprint interval training (SIT; 4 × 30 s all-out interspersed with 4 min recovery) (n = 10). Spatial navigation abilities were assessed using a virtual reality (VR) maze with evaluations at three time points: pre-exercise (TP1), immediately post-exercise (TP2), and 48 h post-exercise (TP3). Angular error (AE) was the primary measure of navigation accuracy. Both MICT and SIT groups exhibited improvements in spatial memory indicated by reductions in AE from TP1 to TP3 (p < 0.001) though the SIT group showed a greater reduction in AE compared to the MICT group (p = 0.039), suggesting a more pronounced benefit from higher-intensity exercise. The control group, however, showed no significant change in AE (p = 0.869), indicating no improvement in spatial memory without exercise intervention. The findings suggest that acute exercise, particularly at higher intensities, enhances spatial memory alongside with learning. It is possible that exercise can be used as a intervention to enhance cognitive functions, particularly spatial navigation.

People are prone to mental fatigue following prolonged work or study, which can lead to a decline in working memory performance. Addressing the adverse effects of mental fatigue on working memory has become a focus of research attention. Aerobic exercise and music are possible intervention methods. Following confirmation of the impact of mental fatigue on working memory, this study developed three intervention protocols (moderate-intensity aerobic exercise, fast-paced music, and aerobic exercise combined with fast-paced music) to investigate their effects on working memory performance under mental fatigue. The results indicated that following the onset of mental fatigue, both aerobic exercise and fast-paced music were effective in restoring working memory performance impaired by mental fatigue, with this positive effect potentially attributed to alterations in alertness. This study may offer insights for individuals seeking to restore working memory under conditions of mental fatigue.

Stretch reflex responses counteract sudden perturbations, and modulation of reflex gains can facilitate voluntary movement. Recent studies suggest movement preparation includes goal-directed tuning of muscle spindles and an equivalent modulation of both short- and long-latency stretch reflex responses (SLR and LLR), as long as the preparatory delay between 'Cue' and 'Go' exceeds 250 ms. The current study aimed to clarify the minimal preparation time required for goal-directed modulation of SLR and LLR responses and to determine how such modulation progressively evolves with extended preparation. We recorded bipolar electromyographic signals of healthy participants to assess reflex responses to mechanical perturbations induced by a robotic manipulandum in the context of a delayed-reach task. Specifically, we examined how multiple preparatory delays (250, 300, 350, 400, 450, and 500 ms) impact the goal-directed modulation of SLR and LLR responses from the loaded or unloaded pectoralis major, anterior deltoid, and posterior deltoid muscles. We found that preparatory delays of 300 ms and 350 ms are sufficient for goal-directed tuning of SLR responses in the posterior deltoid and pectoralis muscles, respectively. Our results also suggest that unloading (i.e., antagonist loading) may facilitate both the earlier emergence and more robust expression of goal-directed SLR tuning. Goal-directed tuning of LLR responses emerged as early as 250 ms of preparation, and such tuning was robust against muscle load conditions, in line with previous findings. We observed no consistent increase in SLR tuning at preparation delays that extended beyond the required minimum, whereas such enhancement was observed at the LLR epoch. These findings clarify the temporal characteristics of goal-directed stretch reflex gains, which likely emerge through the interplay of multiple feedback mechanisms.

Falls on stairs become more likely with age, partly due to deterioration of the sensorimotor systems essential to balance. The vestibular system, critical for balance control, experiences significant deterioration losing up to 40% of its motion-sensing hair cells by age 70. Signal transmittance also appears to increasingly act like a low-pass filter with age, due to several potential mechanisms. This study aimed to explore the vestibular contributions to balance control during stair negotiation to determine if aging increases reliance on low-frequency vestibular signals similar to standing during dynamic tasks. We hypothesized that older adults would exhibit greater low-frequency vestibular stimulus correlated responses than younger adults during walking and stair negotiation. Fifteen young and fifteen older adults performed stair ascent and stair descent, and treadmill walking while receiving electric vestibular stimulation. Vestibular stimulus correlated responses were quantified by measuring coherence and gain between a 0-25 Hz random waveform electric vestibular stimulus electromyographic activity in seven hip and leg muscles. We found older adults generally exhibited greater 'low' frequency (0-10 Hz) coherence relative to younger adults, whereas, younger adults exhibited greater coherence at higher frequencies (10-25 Hz). These findings not only provide evidence in support our hypothesis but also invite a broad discussion of alternative interpretations that may underlie the age-related shift in how different frequency vestibular signals influence muscle activity during dynamic balance tasks. More broadly, this study enhances our understanding of how aging affects thevestibular cues used during stair negotiation and walking.

Perceptual information is processed independently in each hemisphere at some processing stages. This hemispheric asymmetry is reported to decrease in older people, including for haptic sensation. It has been demonstrated that a prolonged bimanual touch with objects of specific sizes induces a perceptual adaptation aftereffect called haptic size adaptation aftereffect: adaptation to a large/small object in each hand alters the subsequent perceived size of tested objects on the hands as smaller/larger than their actual size. Given that the decrease in hemispheric asymmetry reflects an enhanced inter-hemispheric and inter-hands interaction in older people, an age-related difference in the haptic size adaptation aftereffect could be observed in a bimanual adaptation situation. Our first experiment tested this possibility in the situation where adaptation and test were touched in both hands. We found a comparable magnitude of the aftereffect between younger and older people. In the second experiment, we introduced a situation where adaptation was performed in one hand, and tests were performed with either the adapted or non-adapted hand using a haptic-to-visual size matching task. The aftereffect was only clearly observed for the adapted hand in younger people. However, with some procedural modifications, the third experiment again showed a comparable magnitude of aftereffect between younger and older participants for both two-handed and one-handed adaptations on the adapted hand test in the haptic-to-visual size matching task. Our results suggest that similar perceptual and neural mechanisms, including interhemispheric interactions, underlie haptic size perception in younger and older people.

Studies suggest that the vestibulo-ocular reflex (VOR), which is one of compensatory eye movements, exhibits greater stability during active motion compared to passive motion, and this effect may also apply to the operation of ride-on machinery. Moreover, one study suggested that experimentally manipulating the sense of agency (SoA), such as by introducing delays, can influence the stability of such eye movements. Although a preliminary investigation examined compensatory eye movements and perceived maneuverability under two distinct machine dynamics with a preserved SoA, it remains unclear how systematic variations in motion dynamics influence these factors. Therefore, this study aimed to investigate whether systematic variations in the dynamic properties of a ride-on machine, for which perceived maneuverability is modulated, influence the accuracy of operators' eye movements, focusing on continuous compensatory components, including visually enhanced VOR. Participants rode a yaw-rotational platform whose time constant from joystick input to motor torque was systematically manipulated. During the operation, eye movements were recorded while participants fixated on a visual target fixed to the Earth. After each condition, participants reported their perceived maneuverability and cognitive load. As the platform's time constant increased, maneuverability scores decreased, whereas cognitive load increased. Concurrently, the velocity accuracy of compensatory eye movements decreased. Perceived maneuverability was positively correlated with eye velocity gain and negatively correlated with velocity error. These findings suggest that perceived controllability and eye velocity accuracy are closely related under varying machine dynamics and that this relationship may inform the design of high-maneuverability ride-on machinery.

Cerebral amyloid angiopathy (CAA) is a cerebral small vessel disease common among the elderly. Pericyte loss is one of the earliest characteristics of CAA. Although pericyte loss correlates with neuronal loss, the molecular mechanisms by which pericyte loss contributes to neurodegeneration and CAA progression remain poorly understood. This study aimed to explore the role and the mechanism of pericyte loss in CAA using in vivo APP/PS1 mice models and an in vitro neurovascular unit (NVU) model. The findings showed that pericyte coverage and mRNA expression levels of pleiotrophin (PTN) were significantly decreased in the brain of APP/PS1 mice compared with wild-type (WT) littermate mice, while the amyloid-beta peptide (Aβ) load was elevated. Both pericyte loss and Aβ40 fibrils increased the permeability of the blood-brain barrier (BBB) and decreased secretion of PTN in the in vitro NVU model. Notably, pericyte reintroduction attenuated Aβ40-induced apoptosis in all SH-SY5Y neuroblastoma cells across experimental models, and pericytes reversed the apoptosis of SH-SY5Y cells induced by Aβ40 fibrils in these models. Furthermore, Aβ40 fibrils downregulated PTN secretion and induced pericyte apoptosis through activation of the p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK) signaling pathways. Collectively, these data suggest that BBB disruption resulting from pericyte loss serves as an early pathological hallmark in CAA, promoting Aβ40 accumulation and neurodegeneration via MAPK-dependent pathways. These findings highlight the therapeutic potential of pericyte preservation strategies in CAA management.

The visual field is influenced by movements of the body, head, and eye movements during self-motion. Therefore, compensatory eye movements that stabilize the visual field are crucial for perceptual-motor control. In cycling, a type of eye movement known as optokinetic nystagmus may help prevent visual blur and support the use of retinal flow for maintaining dynamic balance. This study aimed to examine the impact of visual environmental manipulation on dynamic balance control in cycling by altering gaze behavior. Participants cycled under three conditions and were instructed to ride as slowly as possible while staying on the path. In the control condition, they cycled along a striped path. In the laser condition, they cycled on the same path while fixating on a laser point projected 4 m ahead of the bicycle. In the monochrome condition, participants cycled along a plain white path. Each condition consisted of five trials. The results showed that the amplitude at the peak frequency of eye movements was significantly lower in the laser condition compared to the control and monochrome conditions. In addition, the cycling distance and duration were significantly shorter in the laser condition compared to the control condition. There were no significant differences in eye movements or cycling performance between the control and monochrome conditions. These results suggest that fixating on a laser point projected at a constant distance ahead suppresses the amplitude of eye movements and impairs balance control during cycling. Natural gaze behavior is likely to be an important factor for cycling safely.