Journal of neurophysiology最新文献

The crustacean cardiac ganglion network coordinates rhythmic contractions of the heart muscle to control the circulation of blood. The specific network of the crab (Cancer borealis) consists of 9 cells: 5 large cell motor neurons (LC1-5) and 4 small endogenous pacemaker cells (SCs). We report a new three-compartmental biophysical LC model that includes synaptic inputs from SCs onto gap-junction coupled spike-initiation-zone (SIZ) compartments. To determine physiologically viable LC models in this realistic configuration, we sampled maximal conductances from a biologically constrained 9D-parameter space, followed by a selection protocol that had three levels. Our results provide previously unknown structure-function insights related to the crustacean cardiac ganglion large cell, including predictions about morphology, SIZ, and the differential roles of active conductances in the three compartments. An analysis of conductance relationships in model neurons revealed a lack of notable correlations among active conductances in the model population, despite clear reports of such relationships in biological neurons. When combined with the interpretations from other model systems, we hypothesize that modes of bursting driven by a strong presynaptic influence (i.e., "forced" bursting) may not require such conductance relationships, whereas endogenous bursters may require them. We further suggest that conductance relationships in a forced burster neuron will more likely serve to shape the characteristics of the firing pattern in the burst, once generated, rather than contribute to a generative mechanism for bursting itself.

The aim of this study was to describe the age-related differences in motor unit behavior during concentric, isometric, and eccentric ankle dorsiflexions. Fourteen young adults (age: 23±3 years) and 12 older adults (age: 68±5 years) performed cycles of concentric/isometric/eccentric ankle dorsiflexions at low velocity (5°/s) and low force level (10% maximum isometric voluntary contraction). Muscle activity was recorded using high-density surface electromyography (HD-sEMG) and decomposed using blind source separation. Motor units were divided into continuous motor units (CNT_MU, e.g., units recruited >=90% of the task duration) and intermittent motor units (INT_MU, e.g., units recruited <90% of the task duration). The average discharge rate (AVR_DR) and discharge rate slopes (SLOPE_DR) were estimated from each extracted motor unit. Joint torque, position and motor unit discharge rate variability were assessed using coefficient of variation (COV). The results revealed that older adults present significantly greater variability in torque, position and discharge rates, especially in dynamic contractions. Regarding motor unit discharge properties statistics, older adults presented reduced AVR_DR for CNT_MU during concentric contractions, whereas their AVR_DR was increased for INT_MU during eccentric contractions compared to young adults, with no differences during isometric contractions. Moreover, older adults presented reduced concentric SLOPE_DR for INT_MU when compared to young adults. Our results demonstrate that older adults present altered neural drive to the muscles, reducing their ability to modulate rate coding and subsequently maintain force steadiness at low force levels in concentric and eccentric contractions.

Human locomotion exhibits remarkable adaptability, allowing individuals to dynamically adjust their gait patten in response to changing environmental demands. Locomotor adaptation on a split-belt treadmill has been a widely studied motor learning technique where two independent treadmill belts move at different speeds, generating adaptation of stepping symmetry over time. This review synthesizes current knowledge on how distinct neural substrates modulate gait in response to the split-belt treadmill through reactive and adaptive processes, highlighting the cerebellum's role in forward model recalibration driven by sensory prediction errors. Particular emphasis is placed on integrating findings across all investigated modulators of locomotor adaptation, including error size, sensory environment, visual feedback, neuromodulation, and cognitive demands, examining both well-established effects on adaptation dynamics and areas where knowledge remains limited. Despite considerable research on the locomotor adaptation paradigm with robust effects on the treadmill, the limited transfer of locomotor adaptation to overground walking remains a major clinical barrier, likely due to the sensory differences between walking contexts. Recent evidence supporting a credit assignment framework is discussed, which suggests that the nervous system attributes motor errors to either shared or context-specific forward models, influencing generalization. Understanding and manipulating this mechanism, with a focus on the sensory environment during adaptation, may be essential to improving the clinical utility of locomotor adaptation and enhancing neurorehabilitation strategies aimed at restoring symmetrical walking in neurological populations.

Gustatory cortical (GC) and basolateral amygdalar (BLA) taste responses consist of an inter-regionally coherent 3-part state sequence. This coherence suggests that reciprocal BLA-GC connectivity is important for taste processing, but it remains unknown: 1) whether BLA-GC coherence actually reflects a reciprocal "conversation" (as opposed to one region simply driving the other); and 2) whether such a "conversation" has anything to do with the taste processing observed within GC response dynamics. Here, we address these questions using network and single-neuron analysis of simultaneously-recorded GC and BLA taste responses in awake rats. We find asymmetric, reciprocal µ-frequency influences that reflect taste processing dynamics: BLA→GC influence dominates between 300 and 1000msec (the epoch in which BLA codes palatability); afterward, when GC responses become palatability-related and GC has been shown to release a behavior-relevant signal, the direction of influence reverses, becoming GC→BLA. Follow-up analyses demonstrate that this "turn-taking" exists alongside effectively synchronous amygdala-cortical coupling-the two regions functioning as a unified structure. Finally, to assess the implications of these interactions for single-neuron responses, we tested the response properties of GC neurons categorized by their inferred connectivity with BLA: GC neurons influenced by BLA produce stronger taste-specific and palatability-related responses than other GC neurons, and the strongest taste encoding is specifically found in GC neurons that both influence and receive influence from BLA-those most deeply embedded in the reciprocal circuit. These results, consistent with findings in multiple systems, support the novel conclusion that taste processing and decision-making is a function of the amygdala-cortical loop.

A clear understanding of how visual information affects postural sway is crucial for assessing normal balance control and developing diagnostic and rehabilitation methods for balance disorders. However, a quantitative model of sway responses to visual perturbations with improved accuracy is still needed. We used virtual reality to apply rotational visual perturbations (0.04-1 Hz, 2.5°-15°) to fourteen healthy adults. Participants were splinted at the knee and hip to ensure the ankle strategy was used. Postural responses, including body angles and ankle torques, were recorded. Initial analysis demonstrated that right-eye dominant subjects showed more coherent body sway responses, possibly related to the higher magnitude of the optical flow in the right half-plane of the visual field. Detailed analysis was therefore focused on eight subjects with large, coherent responses. A detrending method was applied to angles and torques based on inverse Fourier transform to remove frequencies below the smallest stimuli frequency. Our methodology yielded a model with improved accuracy between the visual input and body angle output, i.e., coherence values close to 1. Frequency response analysis revealed a low-pass gain characteristic and a linear phase decrease showing a consistent delay in the system across all amplitudes. A parametric model fitted to the frequency response yielded a delayed, second-order, low-pass transfer function. The transfer function gain decreased with increasing stimulus amplitude, demonstrating a nonlinear response reflecting reduced responsiveness to larger visual amplitudes. In conclusion, this paper provides an experimental and analytical framework to accurately quantify the nonlinear dynamics of postural responses to visual stimuli.

Based on electromyography (EMG) recordings, EMG-EMG coherence provides a practical approach to investigate neural mechanisms involved in locomotion. Although some studies indicated the influence of age and walking conditions on EMG-EMG coherence, no clear consensus emerged from the existing literature. The aim of this scoping review was to map the literature on EMG-EMG coherence in healthy individuals across ages and walking tasks. Six databases (CINAHL, Cochrane Central, CDSR, MEDLINE, Embase, and Web of Science) were searched, resulting in 31 studies included (551 individuals). These studies analyzed EMG EMG coherence of muscles involved during different locomotor tasks. The results revealed a consensus regarding the decrease in EMG-EMG coherence during walking with aging, particularly in the Beta and Gamma bands, which could be attributed to natural alterations in the corticospinal tract with age. Furthermore, Beta and Gamma EMG-EMG coherence showed an increased tendency during proprioceptive (perturbation-based tasks) and proactive (obstacle negotiation) locomotor tasks, which is interpreted as an enhancement of cortical involvement in gait control. This review also highlights the necessity for future research to examine EMG-EMG coherence in frequency bands such as Alpha using standardized signal processing techniques and frequency classifications, and to investigate coherence in children across various locomotor tasks.

Aging commonly leads to balance problems, yet the neural processes driving this decline remain unclear. Recent structural, resting-state, and EEG combined with virtual reality (VR) studies suggest that age-related instability stems from reduced flexibility in combining visual, vestibular, and somatosensory cues rather than from losses in any single system. These findings indicate that diminished neural adaptability is a key contributor to balance impairment and point toward specific network-level mechanisms that future interventions may target.

Purpose: As individuals age, the ability to perceive and interpret tactile stimuli declines, impacting daily function and quality of life. One factor contributing to this decline is cognitive-perceptual load, which refers to the demand placed on limited cognitive resources allocated for processing and attending to sensory stimuli. This study investigates the modulation of cognitive-perceptual load on tactile detection and gap detection in older adults, incorporating concurrent auditory stimuli to replicate real-world multi-sensory environments. Methods: Detection and gap detection of electrotactile stimuli applied to the skin were assessed in two studies, examining a total of 26 right arm dominant older adults. Participants completed tactile detection and gap detection tasks under two conditions, with and without concurrent auditory stimuli. Results: Detecting auditory stimuli significantly impacted the variance of electrotactile stimuli detection (p<0.001), but not mean (p=0.145). In contrast, discriminating auditory stimuli significantly impacted the mean of electrotactile stimuli gap detection (p<0.001), but not variance (p=0.698). Arm dominance significantly impacted the mean of electrotactile stimuli gap detection (p=0.011), but not detection (p=0.936). Participant age significantly impacted the mean of electrotactile stimuli detection (p=0.018), but not gap detection (p=0.558). Conclusion: This work highlights the importance of accounting for cognitive-perceptual load when assessing tactile perception in older adults. Future work can further explore the influence of cognitive-perceptual load in clinical populations (e.g., following a brain injury), and examine additional factors that influence conscious tactile perception.

The development of upper limb movements has been primarily described through reaching movements, which may not have the complex motor planning and execution demands of many daily tasks. In this study, we introduced a complex task in which individuals had to navigate their hand from a start target through two openings in a simple maze to reach an end target. In half the trials, participants received visual feedback of their hand position, and in half of the trials they did not. Thirty-one participants ages 8 to 17 years completed the study. We found that with visual feedback, reaction time, number of speed peaks, movement time, and hand path length all decreased with age. Number of speed peaks, movement time, and hand path length were all increased without visual feedback. Our results demonstrate that complex upper limb movements are refined across childhood and adolescence, potentially reflecting more anticipatory planning and feedforward control. This task can be applied to clinical populations such as cerebral palsy to assess impairments in motor planning and execution as well as determine how proprioceptive impairments contribute to complex movements.

Implicit sensorimotor adaptation-the automatic correction of movement errors-is driven by a perceptual prediction error, the mismatch between the perceived movement outcome and its intended goal. Although perceptual uncertainty is known to attenuate adaptation, the impact of goal uncertainty on adaptation remains unknown. We used a visuomotor adaptation task that isolates implicit adaptation (n = 180), manipulating goal uncertainty by varying how precisely the goal's midpoint could be identified. Display format was varied independently to control for the objective size and luminance of visual features, and targets were hidden at movement onset, ensuring that identical visual input at the moment the error was experienced. We found that goal uncertainty significantly attenuated implicit adaptation, independent of low-level visual and kinematic features. Together, these results demonstrate that a precise internal representation of the goal is critical for sensorimotor adaptation, motivating a fundamental revision of motor learning models to explicitly incorporate goal uncertainty as a key determinant of performance.NEW & NOTEWORTHY Implicit adaptation depends not only on feedback uncertainty but also on goal uncertainty. In a large-scale online visuomotor rotation study (n = 180), increasing spatial ambiguity in the target midpoint-while keeping visual input constant-systematically attenuated implicit adaptation. These results call for a revision of standard models of motor adaptation, positioning the precision of the motor goal as a fundamental component in modulating motor learning.