Experimental Brain Research最新文献

In the complex interplay between sensory and cognitive processes, the brain must sift through a flood of sensory data to pinpoint relevant signals. This selective mechanism is crucial for the effective control of behaviour, by allowing organisms to focus on important tasks and blocking out distractions. The Inhibition of a Recent Distractor (IRD) Task examines this selection process by exploring how inhibiting distractors influences subsequent eye movements towards an object in the visual environment. In a series of experiments, research by Crawford et al. (2005a) demonstrated a delayed response to a target appearing at the location that was previously occupied by a distractor, demonstrating a legacy inhibition exerted by the distractor on the spatial location of the upcoming target. This study aimed to replicate this effect and to investigate any potential constraints when multiple distractors are presented. Exploring whether the effect is observed in more ecologically relevant scenarios with multiple distractors is crucial for assessing the extent to which it can be applied to a broader range of environments. Experiment 1 successfully replicated the effect, showing a significant IRD effect only with a single distractor. Experiments 2-5 explored a number of possible explanations for this phenomenon.

Exercise can induce beneficial improvements in cognition. However, the effects of different modes and intensities of exercise have yet to be explored in detail. This study aimed to identify the effects of different exercise modes (aerobic and resistance) and intensities (low and high) on cognitive performance, adult hippocampal neurogenesis and synaptic plasticity in mice. A total of 40 C57BL/6J mice were randomised into 5 groups (n = 8 mice per group): control, low-intensity aerobic exercise, high-intensity aerobic exercise, low-intensity resistance exercise, and high-intensity resistance exercise. The aerobic exercise groups underwent treadmill training, while the resistance exercise groups underwent ladder climbing training. At the end of the exercise period, cognitive performance was assessed by the Y-maze and Barnes maze. In addition, adult hippocampal neurogenesis was evaluated immunohistochemically by 5-bromo-2'-deoxyuridine (BrdU)/ neuronal nuclei (NeuN) co-labeling. The levels of synaptic plasticity-related proteins in the hippocampus, including synaptophysin (SYP) and postsynaptic density protein 95 (PSD-95), were analyzed by western blotting. Our results showed no significant differences in cognitive performance among the groups. However, high-intensity aerobic exercise significantly increased hippocampal adult neurogenesis relative to the control. A trend towards increased adult neurogenesis was observed in the low-intensity aerobic group compared to the control group. No significant changes in synaptic plasticity were observed among all groups. Our results indicate that high-intensity aerobic exercise may be the most potent stimulator of adult hippocampal neurogenesis.

The vigilance decrement, a temporal decline in detection performance, has been observed across multiple sensory modalities. Spatial uncertainty about the location of task-relevant stimuli has been demonstrated to increase the demands of vigilance and increase the severity of the vigilance decrement when attending to visual displays. The current study investigated whether spatial uncertainty also increases the severity of the vigilance decrement and task demands when an auditory display is used. Individuals monitored an auditory display to detect critical signals that were shorter in duration than non-target stimuli. These auditory stimuli were presented in either a consistent, predictable pattern that alternated sound presentation from left to right (spatial certainty) or an inconsistent, unpredictable pattern that randomly presented sounds from the left or right (spatial uncertainty). Cerebral blood flow velocity (CBFV) was measured to assess the neurophysiological demands of the task. A decline in performance and CBFV was observed in both the spatially certain and spatially uncertain conditions, suggesting that spatial auditory vigilance tasks are demanding and can result in a vigilance decrement. Spatial uncertainty resulted in a more severe vigilance decrement in correct detections compared to spatial certainty. Reduced right-hemispheric CBFV was also observed during spatial uncertainty compared to spatial certainty. Together, these results suggest that auditory spatial uncertainty hindered performance and required greater attentional demands compared to spatial certainty. These results concur with previous research showing the negative impact of spatial uncertainty in visual vigilance tasks, but the current results contrast recent research showing no effect of spatial uncertainty on tactile vigilance.

Background: Multiple sclerosis is a neurodegenerative disease that damages the myelin sheath within the central nervous system. Axonal demyelination, particularly in the corpus callosum, impacts communication between the brain's hemispheres in persons with multiple sclerosis (PwMS). Changes in interhemispheric communication may impair gait coordination which is modulated by communication across the corpus callosum to excite and inhibit specific muscle groups. To further evaluate the functional role of interhemispheric communication in gait and mobility, this study assessed the ipsilateral silent period (iSP), an indirect marker of interhemispheric inhibition and how it relates to gait adaptation in PwMS.

Methods: Using transcranial magnetic stimulation (TMS), we assessed interhemispheric inhibition differences between the more affected and less affected hemisphere in the primary motor cortices in 29 PwMS. In addition, these same PwMS underwent a split-belt treadmill walking paradigm, with the faster paced belt moving under their more affected limb. Step length asymmetry (SLA) was the primary outcome measure used to assess gait adaptability during split-belt treadmill walking. We hypothesized that PwMS would exhibit differences in iSP inhibitory metrics between the more affected and less affected hemispheres and that increased interhemispheric inhibition would be associated with greater gait adaptability in PwMS.

Results: No statistically significant differences in interhemispheric inhibition or conduction time were found between the more affected and less affected hemisphere. Furthermore, SLA aftereffect was negatively correlated with both average percent depth of silent period (dSP%_AVE) (r = -0.40, p = 0.07) and max percent depth of silent period (dSP%_MAX) r = -0.40, p = 0.07), indicating that reduced interhemispheric inhibition was associated with greater gait adaptability in PwMS.

Conclusion: The lack of differences between the more affected and less affected hemisphere indicates that PwMS have similar interhemispheric inhibitory capacity irrespective of the more affected hemisphere. Additionally, we identified a moderate correlation between reduced interhemispheric inhibition and greater gait adaptability. These findings may indicate that interhemispheric inhibition may in part influence responsiveness to motor adaptation paradigms and the need for further research evaluating the neural mechanisms underlying the relationship between interhemispheric inhibition and motor adaptability.

The size-weight illusion is a phenomenon where a smaller object is perceived heavier than an equally weighted larger object. The sensorimotor mismatch theory proposed that this illusion occurs because of a mismatch between efferent motor commands and afferent sensory feedback received when lifting large and small objects (i.e., the application of too little and too much lifting force, respectively). This explanation has been undermined by studies demonstrating a separation between the perceived weight of objects and the lifting forces that are applied on them. However, this research suffers from inconsistencies in the choice of lifting force measures reported. Therefore, we examined the contribution of sensorimotor mismatch in the perception of weight in the size-weight illusion and in non-size-weight illusion stimuli and evaluated the use of a lifting force aggregate measure comprising the four most common lifting force measures used in previous research. In doing so, the sensorimotor mismatch theory was mostly supported. In a size-weight illusion experiment, the lifting forces correlated with weight perception and, contrary to some earlier research, did not adapt over time. In a non-size-weight illusion experiment, switches between lifting light and heavy objects resulted in perceiving the weight of these objects differently compared to no switch trials, which mirrored differences in the manner participants applied forces on the objects. Additionally, we reveal that our force aggregate measure can allow for a more sensitive and objective examination of the effects of lifting forces on objects.

Sinusoidal galvanic vestibular stimulation (sGVS) induces robust modulation of muscle sympathetic nerve activity (MSNA) alongside perceptions of side-to-side movement, sometimes with an accompanying feeling of nausea. We recently showed that transcranial alternating current stimulation (tACS) of the dorsolateral prefrontal cortex (dlPFC) also modulates MSNA, but does not generate any perceptions. Here, we tested the hypothesis that when the two stimuli are given concurrently, the modulation of MSNA would be additive. MSNA was recorded from 11 awake participants via a tungsten microelectrode inserted percutaneously into the right common peroneal nerve at the fibular head. Sinusoidal stimuli (± 2 mA, 0.08 Hz, 100 cycles) were applied in randomised order as follows: (i) tACS of the dlPFC at electroencephalogram (EEG) site F4 and referenced to the nasion; (ii) bilateral sGVS applied to the vestibular apparatuses via the mastoid processes; and (iii) tACS and sGVS together. Previously obtained data from 12 participants supplemented the data for stimulation protocols (i) and (ii). Cross-correlation analysis revealed that each stimulation protocol caused significant modulation of MSNA (modulation index (paired data): 35.2 ± 19.4% for sGVS; 27.8 ± 15.2% for tACS), but there were no additive effects when tACS and sGVS were delivered concurrently (32.1 ± 18.5%). This implies that the vestibulosympathetic reflexes are attenuated with concurrent dlPFC stimulation. These results suggest that the dlPFC is capable of blocking the processing of vestibular inputs through the brainstem and, hence, the generation of vestibulosympathetic reflexes.

Sensorimotor adaptation is a form of motor learning that is essential for maintaining motor performance across the lifespan and is integral to recovery of function after neurological injury. Recent research indicates that experiencing a balance-threatening physical consequence when making a movement error during adaptation can enhance subsequent motor memory. This is perhaps not surprising, as learning to avoid injury is critical for our survival and well-being. Reward and punishment can also differentially modify aspects of motor learning. However, it remains unclear whether other forms of non-physical consequences can impact motor learning. Here we tested the hypothesis that a loud acoustic stimulus linked to a movement error during adaptation could lead to greater generalization and consolidation. Two groups of participants (n = 12 each) adapted to a new, prism-induced visuomotor mapping while performing a precision walking task. One group experienced an unexpected loud acoustic stimulus (85 dB tone) when making foot-placement errors during adaptation. This auditory consequence group adapted faster and showed greater generalization with an interlimb transfer task, but not greater generalization to an obstacle avoidance task. Both groups showed faster relearning (i.e., savings) during the second testing session one week later despite the presence of an interference block of trials following initial adaptation, indicating successful consolidation. However, we did not find significant differences between groups with relearning during session 2. Overall, our results suggest that auditory consequences may serve as a useful method to improve motor learning, though further research is required.

Differences in organization of the primary motor cortex and altered trunk motor control (sensing, processing and motor output) have been reported in people with low back pain (LBP). Little is known to what extent these differences are related. We investigated differences in 1) organization of the primary motor cortex and 2) motor and sensory tests between people with and without LBP, and 3) investigated associations between the organization of the primary motor cortex and motor and sensory tests. We conducted a case-control study in people with (N=25) and without (N=25) LBP. The organization of the primary motor cortex (Center of Gravity (CoG) and Area of the cortical representation of trunk muscles) was assessed using neuronavigated transcranial magnetic stimulation, based on individual MRIs. Sensory tests (quantitative sensory testing, graphaesthesia, two-point discrimination threshold) and a motor test (spiral-tracking test) were assessed. Participants with LBP had a more lateral and lower location of the CoG and a higher temporal summation of pain. For all participants combined, better vibration test scores were associated with a more anterior, lateral, and lower CoG and a better two-point discrimination threshold was associated with a lower CoG. A small subset of variables showed significance. Although this aligns with the concept of altered organization of the primary motor cortex in LBP, there is no strong evidence of the association between altered organization of the primary motor cortex and motor and sensory test performance in LBP. Focusing on subgroup analyses regarding pain duration can be a topic for future research.

Humans can selectively process information and make decisions by directing their attention to desired locations in their daily lives. Numerous studies have shown that attention increases the rate of correct responses and shortens reaction time, and it has been hypothesized that this phenomenon is caused by an increase in sensitivity of the sensory signals to which attention is directed. The present study employed psychophysical methods and electroencephalography (EEG) to test the hypothesis that attention accelerates the onset of information accumulation. Participants were asked to discriminate the motion direction of one of two random dot kinematograms presented on the left and right sides of the visual field, one of which was cued by an arrow in 80% of the trials. The drift-diffusion model was applied to the percentage of correct responses and reaction times in the attended and unattended fields of view. Attention primarily increased sensory sensitivity and shortened the time unrelated to decision making. Next, we measured centroparietal positivity (CPP), an EEG measure associated with decision making, and found that CPP latency was shorter in attended trials than in unattended trials. These results suggest that attention not only increases sensory sensitivity but also accelerates the initiation of decision making.

Prism adaptation (PA) affects visuospatial attention such as spatial orienting in both the right and left hemifields; however, the systematic after-effects of PA on visuospatial attention remain unclear. Visuospatial attention can be affected by non-spatial attentional factors, and postural control difficulty, which delays the reaction time (RT) to external stimulation, may be one such factor. Therefore, we aimed to investigate the influence of postural control difficulty on changes in spatial orienting of attention after leftward PA. Seventeen healthy young adults underwent 15-min and 5-min PA procedures for a leftward visual shift (30 diopters). Participants underwent the Posner cueing test immediately before (pre-evaluation) and in between and after the PA procedures (post-evaluations) while standing barefoot on the floor (normal standing condition) and on a balance-disc (balance standing condition). In the pre-evaluation, RTs in the balance standing condition were significantly longer compared to those in the normal standing condition for targets appearing in both the right and left hemifields. Leftward PA improved the RT for targets appearing in the right, but no left, hemifield in the balance standing condition, such that RTs for targets in the right hemifield in the post-evaluation were not significantly different between the two standing conditions. However, leftward PA did not significantly change RTs for targets in both hemifields in the normal standing condition. Therefore, postural control difficulty may enhance sensitivity to the features of the visuospatial cognitive after-effects of leftward PA.