Journal of neurophysiology最新文献

Autism Spectrum Disorder (ASD) is characterized by deficits in social communication and restricted, repetitive behavioral patterns. While other physiological presentations in individuals with ASD are heterogeneous, neuroimaging studies have consistently revealed a developmental pattern of initial white matter hypermyelination followed by reduced myelination compared to typically developing peers. Multiple studies have demonstrated that core ASD symptoms, including impairments in social skills, language acquisition, learning capabilities, motor performance, and sensory processing, correlate significantly with white matter dysregulation measured through diffusion tensor imaging. Longitudinal studies have shown that decreased gut microbiome diversity, particularly reductions in beneficial bacteria such as Bifidobacterium and Lactobacillus, correlates with symptom severity. Emerging mechanistic evidence suggests bidirectional relationships between microbiome composition and white matter development, both directly through metabolites like short-chain fatty acids (SCFAs) that regulate oligodendrocyte function and subsequent myelination, and indirectly through modulation of neuroinflammatory pathways. By integrating molecular-level gut physiology findings with macro-level brain imaging data, we may identify novel therapeutic approaches targeting the gut-brain axis in ASD management.

Sensory feedback arising from muscles in the lower limb make an important contribution to the activation of muscles on the opposite side. To date little is known about this interlimb communication for muscles of the upper leg. Here we quantify interlimb reflexes of the quadriceps muscles elicited by femoral nerve stimulation. The reflex response of 10 able-bodied participants was analyzed at eight stimulation intensities (0.7x motor threshold (MT) - 100 % maximal M-wave (M-max)), during standing and sitting. EMG signals of the contralateral vastus lateralis (cVL), rectus femoris (cRF), biceps femoris (cBF) and soleus (cSOL) muscle were analyzed. Significant inhibitory long-latency responses were observed at stimulation intensities higher than 0.7xMT, for the cVL and cRF. Onset latencies ranged from 67 ± 12 ms - 70 ± 13 ms during standing and from 61 ± 14 ms - 67 ± 15 ms during sitting. The strongest depression (- 32,39 % compared to baseline EMG activity) was observed for the cRF during standing at 50 % M-max. The cBF showed excitatory long-latency responses during standing (strongest at 100 % M-max with + 52.36 %) and inhibitory once during sitting, as well as small excitatory short-latency responses during standing. The cSOL showed inhibitory long-latency responses (- 18.15 % at 25 % M-max) during standing. In conclusion, the results show that femoral nerve stimulation elicits consistent contralateral reflex responses in the quadriceps muscles. The occurrence at all intensities suggests that group Ia, Ib and II afferents are involved in the pathways.

There is a growing interest in measuring cortical activity during balance control for understanding mechanisms of impaired balance with aging and neurological dysfunction. The most well-characterized electrophysiological signal elicited by a balance disturbance is the perturbation-evoked N1 potential. We previously found associations between the N1 and balance ability, suggesting it may be a potential biomarker of balance health. However, a potential biomarker will be limited by its reliability and clinical feasibility, which has yet to be established. Here, we characterized the reliability of the balance N1 within and between sessions over a one-week interval in 10 younger and 14 older adults, and over a one-year interval in a subset of older adults (n=12). We extracted N1 amplitude and latency from the Cz electrode using an advanced, computationally-intensive approach (64 electrodes, many trials). Test-retest reliability was assessed using the intra-class correlation coefficient (ICC). Internal consistency was quantified by split-half reliability using the Spearman correlation coefficient. N1s varied across individuals, yet within individuals, showed excellent test-retest reliability (ICC>0.9) and internal reliability (r>0.9). N1 amplitude reliability generally plateaued within 6 trials, while more trials were needed to reliably measure latency. Similar results were obtained using a minimal approach (three electrodes, simple preprocessing) and at the component level (largest contributing N1 source). The N1's stability, reliability, and feasibility make it well-suited for potential use as a clinical biomarker. Characterizing N1 reliability in different populations and contexts will be necessary to enhance our understanding, optimize experimental design, and determine its predictive validity (e.g., falls risk).

The stochastic flickering of ion channels is known to cause ongoing membrane potential fluctuations in neurons. This channel noise is often considered negligible in comparison to synaptic noise, yet it can shape the integrative properties of neurons. Here, in vitro recordings of electrosensory pyramidal neurons under synaptic blockade are characterized and shown to contain a non-trivial repertoire of dynamical features. Our analyses reveal an intrinsic noise structure that is much richer than what could be expected based on previous studies: we identify rapid, small-amplitude, shot noise-like events and we quantify how their rate and amplitude are modulated by slower, large-amplitude fluctuations. This cross-relation is evidence that, at the single-neuron level, membrane potential dynamics can exhibit a form of phase-amplitude coupling. We also investigate the appearance of fast, intermittent subthreshold oscillations and conclude that they are manifestation of stochastic linear dynamics, possibly with time-varying parameters. Our results, collectively, highlight that neurons can spontaneously display rich intrinsic behaviour, which is likely to impact how they process synaptic input.

Previous work has shown that compared with young adults, older adults generalize their walking patterns more across environments that impose different motor demands (i.e., split-belt treadmill vs. overground). However, in this previous study, all participants walked at a speed that was more comfortable for older adults than young participants, which leads to the question of whether young adults would generalize more their walking patterns than older adults when exposed to faster speeds that are more comfortable for them. To address this question, we examined the interaction between healthy aging and walking speed on the generalization of a pattern learned on a split-belt treadmill (i.e., legs moving at different speeds) to overground. We hypothesized that walking speed during split-belt walking regulates the generalization of walking patterns in an age-specific manner. To this end, groups of young (<30 y/o) and older (65+ y/o) adults adapted their gait on a split-belt treadmill at either slower or faster walking speeds. We assessed the generalization of movements between the groups by quantifying their aftereffects during overground walking, where larger overground aftereffects represent more generalization, and zero aftereffects represent no generalization. We found an interaction between age and walking speed in the generalization of walking patterns. More specifically, older adults generalized more when adapted at slower speeds, whereas younger adults did so when adapted at faster speeds. These results suggest that comfortable walking speeds lead to more generalization of newly acquired motor patterns beyond the training contexts.

Predictions are combined with sensory information when making choices. Accumulator models have conceptualized predictions as trial-by-trial updates to a baseline evidence level. These models have been successful in explaining the influence of choice history across-trials, however they do not account for how sensory information is transformed into choice evidence. Here, we derive a gated accumulator that models the onset of evidence accumulation as a combination of delayed sensory information and a prediction of sensory timing. To test how delays interact with predictions, we designed a free choice saccade task where participants directed eye movements to either of two targets that appeared with variable delays and asynchronies. Despite instructions not to anticipate, participants responded prior to target onset on some trials. We reasoned that anticipatory responses reflected a trade-off between inhibiting and facilitating the onset of evidence accumulation via a gating mechanism as target appearance became more likely. We then found that anticipatory responses were more likely following repeated choices, suggesting that the balance between anticipatory and sensory responses was driven by a prediction of sensory timing. By fitting the gated accumulator model to the data, we found that variance in within-trial fluctuations in baseline evidence best explained the joint increase of anticipatory responses and faster sensory-guided responses with longer delays. Thus, we conclude that a prediction of sensory timing is involved in balancing the costs of anticipation with lowering the amount of accumulated evidence required to trigger saccadic choice.

We recorded from neurons in primary auditory cortex (A1) and middle-lateral belt area (ML) while rhesus macaques either discriminated amplitude-modulated noise (AM) from unmodulated noise or passively heard the same stimuli. We used several post-hoc pooling models to investigate the ability of auditory cortex to leverage population coding for AM detection. We find that pooled-response AM detection is better in the active condition than the passive condition, and better using rate-based coding than synchrony-based coding. Neurons can be segregated into two classes based on whether they increase (INC) or decrease (DEC) their firing rate in response to increasing modulation depth. In these samples, A1 had relatively fewer DEC neurons (26%) than ML (45%). When responses were pooled without segregating these classes, AM detection using rate-based coding was much better in A1 than in ML, but when pooling only INC neurons, AM detection in ML approached that found in A1. Pooling only DEC neurons resulted in impaired AM detection in both areas. To investigate the role of DEC neurons, we devised two pooling methods that opposed DEC and INC neurons: a direct subtractive method and a two-pool push-pull opponent method. Only the push-pull opponent method resulted in superior AM detection relative to indiscriminate pooling. In the active condition, the opponent method was superior to pooling only INC neurons during the late portion of the response in ML. These results suggest that the increasing prevalence of the DEC response type in ML can be leveraged by appropriate methods to improve AM detection.

How do differences in the constraints of a practiced motor task affect oscillatory functional connectivity between the motor cortex and muscle? Here, we investigate corticomuscular (CM) and intermuscular (IM) coherence during the hold-phase of a dynamic position control (PC) and isometric force control (FC) task. We also investigate the effects of PC motor practice requiring precise wrist flexions to designated target positions, and effects of FC motor practice involving isometric wrist flexions to designated target force levels or rest in a control group. In forty-six young healthy adults (aged 20-30), full-cap electroencephalography (EEG) and electromyography (EMG) were recorded from the flexor and extensor carpi radialis muscles during the tasks. Beta-band (15-35 Hz) CM and IM coherence were investigated as a task-related marker of oscillatory activity in the corticospinal system. At baseline, higher CM coupling was demonstrated during position control compared to force control. Following PC motor practice, CM beta-band coherence increased (P = 0.038), while it remained unchanged for participants who practiced FC or rested. This pattern was also found for IM coherence. The increased oscillatory synchronization following PC practice was driven by greater descending signaling (P = 0.025). We speculate that the observed differences between position and force control relate to task differences in corticomuscular control-strategy and the influence of different sensory modalities during motor practice. We interpret the results as indicating increased coupling between the motor cortex and the motoneuron pool of the contracting muscle following dynamic motor practice emphasizing requirements for position control in motor learning.

Eye movements in vertebrates moving around stabilize retinal images, achieved through the vestibuloocular reflex (VOR) and the optokinetic response (OKR). While VOR compensates for head velocity, its effectiveness declines with prolonged motion, necessitating the OKR. This study explores the three-dimensional (3D) nature of the OKR in goldfish, focusing on horizontal (H), vertical (V), and torsional (T) responses and their adaptation. We found that naïve goldfish exhibited minimal V and TOKR unlike robust HOKR having low-pass characteristics. Through visual training, V and TOKR manifested with flatter frequency spectra, although TOKR toward intorsion unchanged. Memory retention revealed a slower decay of adapted TOKR compared to others. These are the first evaluation of V and TOKR in fish, demonstrating that while naïve goldfish do not rely on V and TOKR in their natural behavior, they retain adaptative capabilities. Vertical and torsional ocular ranges, measured through tilt VOR, well exceeded OKR movement ranges, indicating that minimal VOKR and TOKR are not due to ocular muscle limitations but inherent OKR properties. Head motion analysis in freely-swimming goldfish and carp, a closely related species, revealed small, flat frequency spectra in roll and pitch, and large low-pass spectra in yaw in the former, and a significant pitch-down bias during foraging in the latter. These findings suggest that goldfish OKRs are adaptable across axes, reflecting the unique vestibular and visual experiences associated with goldfish locomotor behavior patterns. Notably, the asymmetrical adaptability of TOKR potentially linked to foraging behaviors.