Journal of neurophysiology最新文献

To track moving targets, humans move their eyes using both saccades and smooth pursuit. If pursuit eye movements fail to accurately track the moving target, catch-up saccades are initiated to rectify the tracking error. It is well known that retinal position and velocity errors determine saccade latency and amplitude, but the extent to which retinal acceleration error influences these aspects is not well quantified. To test this, 13 adult human participants performed an experiment where they pursued accelerating/decelerating targets. During the ongoing pursuit, we introduced a randomly sized target step to evoke a catch-up saccade and analyzed its latency and amplitude. We observed that retinal acceleration error (computed over a 200 ms range centered 100 ms before the saccade) was a statistically significant predictor of saccade amplitude and latency. A multiple linear regression supported our hypothesis that retinal acceleration errors influence saccade amplitude in addition to the influence of retinal position and velocity errors. We also found that saccade latencies were shorter when retinal acceleration error increased the tracking error and vice versa. In summary, our findings support a model in which retinal acceleration error is used to compute a predicted position error ∼100 ms into the future to trigger saccades and determine saccade amplitude.NEW & NOTEWORTHY When visually tracking object motion, humans combine smooth pursuit and saccadic eye movements to maintain the target image on the fovea. Retinal position and velocity errors are known to determine catch-up saccade amplitude and latency, however, it is unknown if retinal acceleration error is also used to predict future target position. This study provides evidence of a small but statistically significant contribution of retinal acceleration error in determining saccade amplitude and latency.

Prolonged local vibration (LV) is thought to promote brain plasticity through repeated Ia afferents discharge. However, the underlying mechanisms remain unclear. This study therefore aimed at determining the acute after-effects of 30-min LV of the flexor carpi radialis muscle (FCR) on sensorimotor (S1, M1) and posterior parietal cortex (PPC) areas activity. Sixteen healthy participants were tested before and immediately after 30 min of FCR LV. Electroencephalographic signals were recorded during isometric submaximal wrist flexions. Time-frequency analyses were performed at source levels during contraction preparation, contraction initiation, force plateau, and relaxation. After LV, the results showed an increase in α and β desynchronizations in the source activity for the estimated M1, S1, and PPC during contraction preparation (P ≤ 0.05) and contraction initiation (P ≤ 0.05; except for PPC in the β band: P = 0.07), and a greater α desynchronization in M1, S1, and PPC (P < 0.01) during force plateau. No LV-induced changes were observed during relaxation. Prolonged LV on the upper limb could increase estimated cortical activity within M1, S1, and PPC areas during subsequent isometric contractions. This could be due to LV-induced Ia afferents inputs projecting onto cortical areas through proprioceptive pathways, and likely triggering brain use-dependent plasticity.NEW & NOTEWORTHY Prolonged local vibration (LV) is thought to promote brain plasticity, yet the underlying mechanisms remain unclear. In the present study, we used electroencephalography in healthy subjects and found increased activity in primary motor, primary somatosensory, and posterior parietal areas after a single exposure to LV. This may be due to LV-induced Ia afferents inputs projecting onto cortical areas through proprioceptive pathways, and likely triggering brain plasticity.

In many species, olfactory abilities in females are more acute than those in males. Studies in humans show that women have lower olfactory thresholds and are better able to discriminate and identify odors than men. In mice, odorants elicit faster activation from a larger number of olfactory bulb glomeruli in females than in males. Our study explores sex differences in olfaction in Long Evans rats from a behavioral and electrophysiological perspective. Local field potentials (LFPs) in the olfactory bulb (OB) represent the coordinated activity of bulbar neurons. Olfactory gamma (65-120 Hz) and beta (15-30 Hz) oscillations have been functionally linked to odor perception. Spontaneous and odor-evoked OB LFPs were recorded from awake rats at the same time for 12 days. Odors used included urine of both sexes and monomolecular odorants characterized previously for correlation of volatility with behavior and OB oscillations. Sampling duration in a habituation context, baseline gamma and beta power, and odor-elicited beta and gamma power were analyzed. We find that females sample odorants for a shorter duration than males (just over 1-s difference). Although baseline gamma and beta power do not show significant differences between the two sexes, odor-elicited gamma and beta power in females is significantly lower than in males. Neither sampling duration nor beta and gamma power in females varied systematically with day of estrus. We further verify that variance of these behavioral and physiological measures is not different across sexes, adding to growing evidence that researchers need not be concerned about often-claimed additional variance in female subjects.NEW & NOTEWORTHY Olfaction plays a large role in evolutionary processes. However, we know little about sex differences in olfactory bulb neurophysiology, and many scientists believe that females are more variable because of estrus. We show that female rats sniff odors for shorter durations than males and have lower power in neural oscillations related to cognition. Estrus was not related to variance in any measures. Finally, males and females show equal variance on these behavioral and physiological processes.

Diabetic peripheral neuropathy (DPN) affects approximately half of the 500 million people with type 2 diabetes worldwide. Previous studies have suggested that glucagon-like peptide-1 (GLP-1) receptors in the peripheral nervous system may be a suitable target for DPN treatment. Fourteen participants were consecutively recruited after being prescribed either semaglutide or dulaglutide as part of standard clinical care for type 2 diabetes. Participants underwent clinical assessment, nerve conduction studies, and axonal excitability assessment at baseline and at 3 mo following commencement of GLP-1 receptor agonist (GLP-1RA) therapy. These data were combined with 10 participants who had previously received exenatide therapy, and mathematical modeling of excitability data was undertaken. Clinical neuropathy scores improved at 3 mo following commencement of GLP-1 (baseline TNS 3.7 ± 4.5, posttreatment TNS 2.3 ± 3.4, P = 0.005). Nerve conduction studies demonstrated an improvement in sural amplitude at 3 mo (baseline 11.9 ± 8.5 μV, posttreatment 14.2 ± 9.2 μV; P = 0.013). Axonal excitability studies revealed changes consistent with improvements in Na⁺/K⁺-ATPase pump function and Na⁺ permeability, and this was supported by mathematical modeling. GLP-1RA therapy improves clinical and neurophysiological outcomes in DPN. Treatment with GLP-1RA may reverse axonal dysfunction by improving Na⁺/K⁺-ATPase pump function.NEW & NOTEWORTHY Diabetic peripheral neuropathy is known to be relentlessly progressive and irreversible. Prospective studies in 24 participants with diabetic peripheral neuropathy (DPN) treated with glucagon-like peptide-1 receptor agonists (GLP-1RA) demonstrated improvements in clinical neuropathy scores, nerve conduction studies, and axonal excitability recordings. Analysis of axonal excitability recordings revealed the mechanism for GLP-1RA improvement in DPN were changed consistent with improvements in Na⁺/K⁺-ATPase pump function, and this was supported by mathematical modeling.

Human body movements are supported by a somatotopic map, primary motor cortex (M1), that is found along the precentral gyrus. Recent evidence has suggested two further motor maps that span the lateral occipitotemporal cortex (LOTC) and the precuneus. Confirmation of these maps is important, as they influence our understanding of the organization of motor behavior, for example by revealing how visual- and motor-related activity interact. However, evidence for these recently proposed maps is limited. We analyzed an open functional MRI (fMRI) dataset of 62 participants who performed 12 different body part movements. We analyzed the magnitude of responses evoked by movements with novel quantitative indices that test for maplike organization. We found strong evidence for bilateral somatotopic maps in precentral and postcentral gyri. In LOTC, we found much weaker responses to movement and little evidence of somatotopy. In the precuneus, we found only limited evidence for somatotopy. We also adopted a background connectivity approach to examine correlations between M1, LOTC, and the precuneus in the residual time series data. This revealed a ventral-posterior/dorsal-anterior distinction in the connectivity between precuneus and M1, favoring the head and arms, respectively. Posterior right hemisphere LOTC showed some evidence of preferential connectivity to arm-selective regions of M1. Overall, our results do not support the existence of a somatotopic motor map in LOTC but provide some support for a coarse map in the precuneus, especially as revealed in connectivity patterns. These findings help clarify the organization of human motor representations beyond the precentral gyrus.NEW & NOTEWORTHY We investigated previous claims about the existence of somatotopic motor maps in the human lateral occipitotemporal cortex (LOTC) and the precuneus, in comparison to known maps in the precentral and postcentral gyri. Consistent with previous findings, we identified clear somatotopic motor maps in the latter two regions. With multiple quantitative measures of activity and connectivity, however, we found no evidence for a map in the LOTC and limited evidence for a map in the precuneus.

Although the dominant hand has been shown to have performance advantages over the nondominant hand, these interlimb differences have found to be dependent on task and biomechanical demands. The dynamic dominance hypothesis suggests that the left hemisphere is specialized for the control of intersegmental dynamics while the nondominant right hemisphere is specialized for postural control, in right-handers. In a real-world scenario, however, cognitive challenges might be expected to modulate these specialized behaviors. Therefore, we hypothesized that with increased cognitive load, lateralized motor control processes would become even more asymmetrical. We recruited 16 right-handed older adults (11 females, 5 males; 65.88 yr ± 1.99 SE) to perform 170 trials of a unilateral reaching task with each of their hands on the Kinereach system. In each trial, participants rapidly memorized pictorial instructions before identifying and reaching for the correct object on a screen. The complexity of the task increased over the course of the experiment. Our results demonstrated higher reaction times in the right than in the left hand (P = 0.0004). Movements became increasingly curved and erroneous with cognitive load, but interlimb differences in movement quality were absent. We found higher joint cocontraction in the right than in the left arm (P < 0.05), but these differences were unaffected by cognitive load. Hence, with the addition of a cognitive load, we observed asymmetries in reaction time but not in joint coordination or movement quality. This highlights the role of cognitive load in modulating limb/hemisphere specializations for control processes.NEW & NOTEWORTHY Although we know that motor control processes are lateralized to each hemisphere, the role of cognitive load on these specialized processes is undefined. We designed a unique task that incorporates a cognitive challenge to a typical reaching movement to examine how cognitive load affects limb asymmetries in motor control. In a group of typical older adults, we demonstrated interlimb asymmetries in reaction time but not in joint coordination or movement quality.

When we run our hand across a surface, each finger typically repeats the sensory stimulation that the leading finger has already experienced. Because of this redundancy, the leading finger may attract more attention and contribute more strongly when tactile signals are integrated across fingers to form an overall percept. To test this hypothesis, we re-analyzed data collected in a previous study (Arslanova I, Takamuku S, Gomi H, Haggard P, J Neurophysiol 128: 418-433, 2022), where two probes were moved in different directions on two different fingerpads and participants reported the probes' average direction. Here, we evaluate the relative contribution of each finger to the percept and examine whether multidigit integration gives priority to the leading finger. Although the hand actually remained static in these experiments, a "functional leading finger" could be defined with reference to the average direction of the stimuli and the direction of hand-object relative motion that this implied. When participants averaged the motion direction across fingers of the same hand, the leading finger received a higher weighting than the nonleading finger, even though this biased estimate of average direction. Importantly, this bias disappeared when averaging motion direction across the two hands. Both the reported average direction and its systematic relation to the difference between the individual stimulus directions were explained by a model of motion integration in which the sensory weighting of stimuli depends on the directions of the applied stimuli. Our finding supports the hypothesis that the leading finger, which often receives novel information in natural hand-object interactions, is prioritized in forming our tactile perception.NEW & NOTEWORTHY The capacity of the tactile system to process multiple simultaneous stimuli is restricted. One solution could be to prioritize input from more informative sources. Here, we show that sensory weighting accorded to each finger during multidigit touch is biased in a direction-dependent manner when different motions are delivered to the fingers of the same hand. We argue that tactile inputs are weighted based on purely geometric information to prioritize "novel" information from the leading finger.

Prior research has highlighted the therapeutic benefits of acute intermittent hypoxia (AIH) in enhancing motor performance after motor incomplete spinal cord injury and in able-bodied individuals. Although studies in rodents and humans indicate that AIH may facilitate motor excitability, the relationship between excitability changes and functional performance remains unclear. In addition, discrepancies in the effects of AIH on excitability in able-bodied individuals merit further investigation. Understanding the concurrent impact of repetitive AIH on voluntary activation and spinal reflex excitability may clarify the functional implications of AIH for muscle force production. High voluntary activation is vital for sustaining torque production during activities that require repeated muscle contractions. We hypothesized that repetitive AIH would attenuate decreases in both voluntary activation and maximum torque production typically observed during fatiguing contractions. To test this hypothesis, we examined the effects of four consecutive days of AIH on voluntary activation and torque generation during repeated maximal plantar flexion contractions. We assessed changes in voluntary activation using the central activation ratio by calculating the ratio of voluntary torque to the torque produced with supramaximal electrical stimulation. Consistent with our hypothesis, we show that repetitive AIH significantly increases both voluntary activation and peak torque during fatiguing contractions. We did not observe any changes in resting spinal reflex excitability or antagonist muscle coactivation during fatiguing contractions post-AIH. Together, these findings suggest that repetitive AIH reduces performance fatigability through enhanced descending neural drive. Optimizing voluntary activation is critical for facilitating the recovery of functional walking skills after neurological injury.NEW & NOTEWORTHY This study shows that repetitive acute intermittent hypoxia (AIH) significantly increases both voluntary activation and peak torque during fatiguing lower limb contractions. However, resting spinal reflex excitability and antagonist muscle coactivation during fatiguing contractions did not change following repetitive AIH. Together, these observations indicate that repetitive AIH reduces performance fatigability through enhanced descending neural drive. These findings underscore the therapeutic potential of AIH for promoting motor recovery after neurological injury.