Experimental Brain Research最新文献

The movement preparation of bimanual asymmetric reaching movements is longer than bimanual symmetric movements. This bimanual asymmetric cost is small for spatially cued movements and large with symbolic cues. Previous research on these bimanual asymmetric costs has relied on mean reaction time. The goal of the present study was to better understand the sensorimotor mechanisms of spatially and symbolically cued bimanual asymmetric costs by employing reaction time distribution analysis. Reaction time distributions were described with the ex-Gaussian parameters of [Formula: see text], [Formula: see text], and [Formula: see text]. Forty-eight young adults made bimanual symmetric and asymmetric reaching movements that were spatially or symbolically cued. With spatial cues, there was a small cost to [Formula: see text] for bimanual asymmetric movements compared to symmetric ones. This was depicted as a 4.8 ms rightward shift to the reaction time distribution. The bimanual asymmetric cost with spatial cues is likely caused by the temporal coupling of bimanual asymmetric movements. With symbolic cues, there was a large cost to [Formula: see text] and small costs to [Formula: see text] and [Formula: see text]. This was depicted as the Gaussian and exponential components of the distribution having longer and more disperse reaction time for asymmetric movements. The bimanual asymmetric cost with symbolic cues is likely caused by two factors: stimulus-response translation of two different symbolic cues and temporal coupling of bimanual asymmetric movements. The bimanual asymmetric cost to µ with symbolic cues is likely a combination of both factors, with stimulus-response translation contributing more than temporal coupling. The bimanual asymmetric costs to σ and τ are exclusively caused by stimulus-response translation.

The photic sneeze reflex (PSR) is an involuntary sneezing response to bright light exposure, affecting approximately 25% of the population. Despite its long history in scientific literature, the underlying mechanisms remain unclear. Several theories, including optic-trigeminal summation, parasympathetic hypersensitivity, and parasympathetic generalization, have been proposed, but none have been conclusively validated. Reproducing the PSR reliably in a laboratory setting is crucial for understanding its neural underpinnings, yet the specific light parameters that trigger PSR are not well-defined. This mini-review aims to consolidate current knowledge on the light stimulus parameters (intensity, spectral composition, wavelength, duration, timing, spatial configuration) that elicit the PSR. A comprehensive literature search was conducted using MEDLINE (PubMed), Google Scholar, Google Books, and Google, employing terms related to photic sneezing in multiple languages. Articles from 2020 to 2024 were screened, resulting in 167 records, with seven studies focusing on stimulus parameters included in this review. The reviewed studies, including four case reports and three laboratory experiments, consistently support that bright light can induce sneezing in susceptible individuals. However, there is significant variability in the methodologies and outcomes, limiting comparability and indicating a need for systematic investigation. No study has yet examined the parametric relationship between light parameters and the PSR. The heterogeneity of methods and findings in the existing literature highlights the lack of standardized research on the specific light parameters that trigger the PSR. This review underscores the need for controlled experiments to clarify these relationships and improve our understanding of the underlying neural mechanisms. Existing research on photic sneezing stimulus parameters is fragmented and lacks systematic approaches. Future studies should focus on standardized, parametric investigations to elucidate the light-sensitive mechanisms of the PSR.

The effect of neck muscle fatigue induced by prolonged isometric contraction of the neck extensor muscles on self-motion perception was studied. The magnitude of self-motion perception was assessed by evaluating the tracking of a remembered earth-fixed visual target during passive symmetric and asymmetric sinusoidal horizontal body rotation. The trunk was rotated on a stationary head for examining the role of neck proprioception and the whole-body for that of the vestibular system. To induce neck extensor muscle fatigue, participants held their head extended against a load for several minutes. Perceptual responses were examined before and during neck muscle fatigue. It was found that the perception of the movement was diminished by neck muscle fatigue as shown by a reduction of the amplitude of the tracking during trunk rotation. This suggests that fatigue affects the motion perception when the neck proprioceptive system was activated by the rotation. This effect has been observed only during slow rotation, while the responses remained unmodified during fast rotation. In contrast, neck muscle fatigue did not affect the tracking when rotation activated only the vestibular system. Furthermore, neck muscle fatigue abolished the effect of tonic head deviation on perceptual responses to whole-body rotation. Therefore, neck muscle fatigue alters the self-motion perception reducing the ability of the proprioceptive system to signal slow trunk rotations and the position of the head relative to the trunk during body movements.

The control of human balance involves an interaction between the human motor, cognitive, and sensory systems. The dynamics of this interaction are yet to be fully understood, however, work has shown the performance of cognitive tasks to have a hampering effect on motor performance, while additive sensory noise to have a beneficial effect. The current study aims to examine whether postural control will be impacted by a concurrent working memory task, and similarly, if additive noise can counteract the expected negative influence of the added cognitive demand. Postural sway of healthy young adults was collected during the performance of a modified N-back task with varying difficulty, in the presence and absence of auditory noise. Our results show a reduction in postural stability scaled to the difficulty of the cognitive task, but this effect is less prominent in the presence of additive noise. Additionally, by separating postural sway into different frequency bands, typically used to assess the exploratory vs feedback-driven stabilizing dynamics of sway, we found a differential effect between the cognitive task and additive noise, thus demonstrating that both frequency regimes of postural sway are sensitive to high cognitive load and increased sensory information.

Age-related hand motor impairments may critically depend on visual information though few studies have examined eye movements during tasks of hand function in older adults. The purpose of this study was to assess eye movements and their association with performance while tracing on a touchscreen in young and older adults. Eye movements of 21 young (age 20-38 years; 12 females, 9 males) and 20 older (65-85 years; 10 females, 10 males) adults were recorded while performing an Archimedes spiral tracing task, a common clinical assessment sensitive to age-associated impairments in hand function. Participants traced an Archimedes spiral template on a touchscreen as accurately as possible under three conditions, using (1) a stylus, (2) the index finger, and (3) the index finger while performing a visuospatial dual task. Older adults made fewer total fixations than young adults, and participants made fewer fixations when tracing parts of the spiral where vision of the spiral template was likely more obstructed by the hand. Inter-fixation distance and inter-fixation distance variability were greater in older compared to young adults. A relationship between increased inter-fixation distance and increased spiral tracing error demonstrates the association between age-related changes in eye movements and spiral tracing performance in older adults. Results contribute novel findings of age-associated changes in ocuomotor behavior during a common clinical assessment and offer insight into motor control in older adults.

Vibrating muscles to manipulate proprioceptive input creates the sensation of an apparent change in body position. This study investigates whether vibrating the right biceps muscle has similar effects as vibrating the left posterior neck muscles. Based on previous observations, we hypothesized that both types of muscle vibration would shift the perception of healthy subjects' subjective straight-ahead (SSA) orientation in the horizontal plane to the left. Such a finding would be extremely interesting for future treatment of spatial neglect, a disorder following right-sided stroke brain lesions. Twenty healthy participants (11 females, 9 males, aged 20-52) were tested under five conditions: baseline (no vibration), vibration of left neck muscles, vibration of right biceps with the arm fixed to the wall, vibration of right biceps with the arm lying on a table, and vibration of right triceps with the arm fixed to the wall. Participants had to align a laser pointer (by verbal instructions) with their perceived SSA position in complete darkness. ANOVA revealed significant SSA shifts with neck and biceps vibrations but not with triceps vibration. The largest leftward SSA shift occurred with right biceps vibration while the arm was lying on the table (-6.1°), followed by left neck muscle vibration (-6.0°), and right biceps vibration with the arm fixed to the wall (-5.4°). Post-hoc power analyses showed high power (> 0.98) for the significant differences compared to the baseline condition. The finding that right biceps vibration affects SSA perception similarly to left neck muscle vibration offers potential for clinical applications in treating spatial neglect. Future research should explore the therapeutic efficacy of vibrating the right biceps in neurological patients with spatial neglect.

Transcranial magnetic stimulation (TMS) has been used for many years to study the pathophysiology of amyotrophic lateral sclerosis (ALS). Based on single- or dual-pulse TMS and EMG and/or single motor unit (MU) recordings, many groups have described a loss of central inhibition as an early marker of ALS dysfunction, reflecting a state of cortical 'hyperexcitability'. This conclusion is not without its detractors, however, leading us to reexamine this issue using 4-pulse TMS, shown previously to be more effective for testing central motor pathway functional integrity. A total of 221 motor units were tested in 13 subjects (6 controls; 7 with ALS) across a total of 798 unique TMS conditions. MUs were studied from hand muscles (usually first dorsal interosseus) and from tibialis anterior (TA). Subjects were required to recruit a MU to fire rhythmically, during which time 4-pulse trains of TMS were delivered. A given motor unit's recruitment was examined for different stimulus intensities and interpulse intervals (IPI). All motor units from control subjects showed short latency excitation to TMS, and short latency inhibition for TMS pulses of slightly weaker intensity (i.e. the threshold for inhibition was lower than that for excitation). The same was largely true for MUs studied in subjects with ALS, with the primary difference between control and ALS subjects being the need for stronger stimulus intensities to effect recruitment in subjects with ALS. We saw no evidence for a loss or reduction of inhibition of central motor output in persons with ALS, at least when tested during voluntary contractions.

Voxel-based morphometry (VBM) of T1-weighted (T1-w) magnetic resonance imaging (MRI) is primarily used to study the association of brain structure with cognitive functions. However, in theory, T2-weighted (T2-w) MRI could also be used in VBM studies because of its sensitivity to pathology and tissue changes. We aimed to compare the T1-w and T2-w images to study brain structures in association with cognitive abilities. VBM analysis was applied to T1-w and T2-w MRI data of 120 healthy participants aged 20 to 40. The MRI data was collected using a 3T machine, and it was analyzed with CAT12 to extract maps of Gray matter(GM). We used six cognitive tasks to assess cognitive abilities, including the balloon analog risk task (BART), block design, forward and backward digit span (FDST and BDST), and trail-making tasks A and B. Compared to T2-w, T1-w data showed more brain voxels in the BART, block design, FDST, TMT-A, and TMT-B tasks. However, T2-w imaging identified a greater number of voxels in the BDST. T1-w images identified more correlated brain regions with cognitive scores in the FDST, TMT-A, and B tasks than T2-w. In BART and Block design tasks, both methods revealed the same number of correlated regions, and T2-w just showed more regions than T1-w in the BDST. Findings revealed distinct patterns of sensitivity between T1-w and T2-w imaging in detecting brain regions associated with cognition. The two approaches demonstrated different strengths in identifying areas correlated with cognitive abilities. This study provides valuable guidance for selecting appropriate methods for identifying the optimal approach for detecting brain regions that exhibit the strongest correlations with cognitive abilities.

Vestibular dysfunction has been reported as a potential cause in adolescent idiopathic scoliosis (AIS). However, it remained unclear how stochastic galvanic vestibular stimulation (GVS) affected kinetic performance of patients with AIS. This study aimed to investigate the effect of stochastic GVS on ground reaction forces (GRF) measures during obstacle negotiation among patients with AIS. Fifteen patients with AIS and 15 age/sex-matched healthy controls (HC) participated in this study. Stochastic GVS was applied via electrodes placed over bilateral mastoid process with the intensity of 80% of individual sensory thresholds. Six walking trials including 2 types of GVS (stochastic GVS/sham stimulation) and 3 obstacle conditions (Level/Low/High) were randomly allocated to each participant, and each trial was repeated 3 times. Four AMTI force plates were used to measure GRF peaks and impulses in anterior-posterior (AP₁/AP₂), medial-lateral (ML₁/ML₂), and vertical (V₁/V₂) directions. Significant interactions were observed in AP₁ (F_2,56=3.537, p = 0.036), V₁ (F_2,56=4.118, p = 0.021), ML₁ (F_2,56=3.313, p = 0.044) and medial-lateral impulses (F_2,56=4.386, p = 0.017) for the step negotiating obstacles. Post-hoc comparisons showed that in comparison to sham stimulation, the application of stochastic GVS significantly (1) increased AP₁ (Low: p = 0.038) and V₁ (Low: p < 0.001; High: p = 0.035) in two groups; (2) decreased ML₁ of two groups (AIS: ps < 0.01; HC: ps < 0.05) and medial-lateral impulses in patients with AIS (Low: p = 0.013; High: p = 0.015) during obstacle negotiation. Additionally, the rates of change in ML₁ and medial-lateral impulses among patients with AIS were significantly higher than that of HC, indicating that stochastic GVS demonstrated a greater effect of decreasing ML₁ and medial-lateral impulses in AIS. Stochastic GVS ameliorated kinetic performance of patients with AIS during obstacle negotiation, and its potential mechanism may involve the induction of stochastic resonance phenomenon to enhance vestibular perception. Our study offered stochastic GVS as a novel approach to target vestibular-related postural instability in AIS.

Tachistoscopic studies have established a right field advantage for the perception of visually presented words, which has been interpreted as reflecting a left hemispheric specialization. However, it is not clear whether this is driven by the linguistic task of word processing, or also occurs when processing properties such as the style and regularity of text. We had 23 subjects perform a tachistoscopic study while they viewed five-letter words in either computer font or handwriting. The task in one block was to respond if the word in the peripheral field matched a word just seen in the central field. In a second block with the same stimuli, the task was to respond if the style (handwriting or font) matched. We found a main effect of task: there was a right-field advantage for reading the word, but no field advantage for reporting the style of text. There was no effect of stimulus type and no interaction between task and stimulus type. We conclude that the field advantage for processing text is driven by the task, being specific for the processing the identity of the word and not the perception of the style of the text. We did not find evidence to support prior assertions that the type of text and its regularity influenced the field advantage during the word-reading task.