Adaptation of sensorimotor coupling in postural control Is impaired by sleep deprivation

The purpose of the study was to investigate the effects of sleep deprivation (SD) in adaptation of the coupling between visual information and body sway in young adults'postural control due to changes in optic flow characteristics. Fifteen young adults were kept awake for approximately 25 hours and formed the SD group, while fifteen adults who slept normally the night before the experiment participated as part of the control group. All participants stood as still as possible in a moving room before and after being exposed to one trial with higher amplitude and velocity of room movement. Postural performance and the coupling between visual information, provided by a moving room, and body sway were examined. Results showed that after an abrupt change in visual cues, larger amplitude, and higher velocity of the room, the influence of room motion on body sway was decreased in both groups. However, such a decrease was less pronounced in sleep deprived as compared to control subjects. Sleep deprived adults were able to adapt motor responses to the environmental change provided by the increase in room motion amplitude. Nevertheless, they were not as efficient as control subjects in doing so, which demonstrates that SD impairs the ability to adapt sensorimotor coupling while controlling posture when a perturbation occurs.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Descending Inputs to Spinal Circuits Facilitating and Inhibiting Human Wrist Flexors

Recently we reported in humans that electrical stimulation of the wrist extensor muscle extensor carpi radialis (ECR) could facilitate or suppress the H reflex elicited in flexor carpi radialis (FCR), for inter-stimulus intervals (ISIs) of 30 ms or 70 ms, respectively. The facilitation at 30 ms may be produced by both flexor afferents and extensor Ib afferents acting on a spinal circuit; the origin of the suppression at 70 ms is less certain. In this study, we investigated possible descending inputs to these systems. We used magnetic stimulation of the contralateral primary motor cortex, and click sound stimulation, to activate the corticospinal and the reticulospinal tracts respectively, and measured the effects on the H reflex conditioned by ECR stimulation. Corticospinal inputs reduced both the 30 ms facilitation and 70 ms suppression, indicating corticospinal inhibition of both circuits. By contrast, we failed to show any effect of clicks, either on the H reflex or on its modulation by ECR stimulation. This suggests that click-activated reticulospinal inputs to these circuits may be weak or absent

Mean and standard deviation values of position and velocity variability in pre- and post-change trials for both sleep deprivation (SD) and control groups.

<p>Note: (*) represent significant pairwise comparisons, which was used for group x trial interaction for both position and velocity variability.</p

Mean and standard deviation values of mean sway amplitude in pre- and post-change trials for both sleep deprivation (SD) and control groups.

<p>Note: (*) represent significant pairwise comparisons, which was used for a group x trial interaction.</p

Mean and standard deviation values of gain and phase in all room movement cycles in pre-change, change, and post-change trials for both sleep deprivation (SD) and control groups.

<p>Mean and standard deviation values of gain and phase in all room movement cycles in pre-change, change, and post-change trials for both sleep deprivation (SD) and control groups.</p

Time-series and amplitude spectra of body oscillation and moving room displacement of a representative subject of the control group during a pre-change trial.

<p>Time-series and amplitude spectra of body oscillation and moving room displacement of a representative subject of the control group during a pre-change trial.</p

Schematic representation of the experimental design employed in this study.

<p>Number of trials and room movement parameters are described for pre-change, change, and post-change trials. Results for all dependent variables were averaged for each subject in the three trials of both pre- and post-change trials. Results of change trials were not included the in analyses.</p

Effect of central lesions on a spinal circuit facilitating human wrist flexors

Abstract A putative spinal circuit with convergent inputs facilitating human wrist flexors has been recently described. This study investigated how central nervous system lesions may affect this pathway. We measured the flexor carpi radialis H-reflex conditioned with stimulation above motor threshold to the extensor carpi radialis at different intervals in fifteen patients with stroke and nine with spinal cord injury. Measurements after stroke revealed a prolonged facilitation of the H-reflex, which replaced the later suppression seen in healthy subjects at longer intervals (30–60 ms). Measurements in patients with incomplete spinal cord injury at cervical level revealed heterogeneous responses. Results from patients with stroke could represent either an excessive facilitation or a loss of inhibition, which may reflect the development of spasticity. Spinal cord injury results possibly reflect damage to the segmental interneuron pathways. We report a straightforward method to assess changes to spinal circuits controlling wrist flexors after central nervous system lesion

Spasms after spinal cord injury show low-frequency intermuscular coherence

Intermuscular coherence allows the investigation of common input to muscle groups. Although beta-band (15-30 Hz) intermuscular coherence is well understood as originating from the cortex, the source of intermuscular coherence at lower frequencies is still unclear. We used a wearable device that recorded electromyographic (EMG) signals during a 24-h period in four lower limb muscles of seven spinal cord injury patients (American Spinal Cord Injury Association impairment scale: A, 6 subjects; B, 1 subject) while they went about their normal daily life activities. We detected natural spasms occurring during these long-lasting recordings and calculated intermuscular coherence between all six possible combinations of muscle pairs. There was significant intermuscular coherence at low frequencies, between 2 and 13 Hz. The most likely source for this was the spinal cord and its peripheral feedback loops, because the spinal lesions in these patients had interrupted connections to supraspinal structures. This is the first report to demonstrate that the spinal cord is capable of producing low-frequency intermuscular coherence with severely reduced or abolished descending drive. NEW & NOTEWORTHY This is the first report to demonstrate that intermuscular coherence between lower limb muscles at low frequencies can be produced by the spinal cord with severely reduced or abolished descending drive