Single cell and ensemble activity of lumbar intermediate and ventral horn interneurons in the spinal air-stepping cat

We explored the relationship between population interneuronal network activation and motor output in the adult, in-vivo, air stepping, spinal cat. By simultaneously measuring the activity of large numbers of spinal interneurons, we explored ensembles of coherently firing interneurons and their relation to motor output. Additionally, the networks were analyzed in relation to their spatial distribution along the lumbar enlargement for evidence of localized groups driving particular phases of the locomotor step cycle. We simultaneously recorded hindlimb EMG activity during stepping and extracellular signals from 128 channels across two polytrodes inserted within lamina V-VII of two separate lumbar segments. Results indicated that spinal interneurons participate in one of two ensembles that are highly correlated with the flexor or the extensor muscle bursts during stepping. Interestingly, less than half of the isolated single units were significantly unimodally tuned during the step cycle while >97% of the single units of the ensembles were significantly correlated with muscle activity. These results show the importance of population scale analysis in neural studies of behavior as there is a much greater correlation between muscle activity and ensemble firing than between muscle activity and individual neurons. Finally, we show that there is no correlation between interneurons' rostrocaudal locations within the lumbar enlargement and their preferred phase of firing or ensemble participation. These findings indicate that spinal interneurons of lamina V-VII encoding for different phases of the locomotor cycle are spread throughout the lumbar enlargement in the adult spinal cord.

Putting the theory into 'burstlet theory': A biophysical model of bursts and burstlets in the respiratory preBötzinger complex

Inspiratory breathing rhythms arise from synchronized neuronal activity in a bilaterally distributed brainstem structure known as the preBötzinger complex (preBötC). In in vitro slice preparations containing the preBötC, extracellular potassium must be elevated above physiological levels (to 7-9mM) to observe regular rhythmic respiratory motor output in the hypoglossal nerve to which the preBötC projects. Reexamination of how extracellular K+ affects preBötC neuronal activity has revealed that low amplitude oscillations persist at physiological levels. These oscillatory events are sub-threshold from the standpoint of transmission to motor output and are dubbed burstlets. Burstlets arise from synchronized neural activity in a rhythmogenic neuronal subpopulation within the preBötC that in some instances may fail to recruit the larger network events, or bursts, required to generate motor output. The fraction of subthreshold preBötC oscillatory events (burstlet fraction) decreases sigmoidally with increasing extracellular potassium. These observations underlie the burstlet theory of respiratory rhythm generation. Experimental and computational studies have suggested that recruitment of the non-rhythmogenic component of the preBötC population requires intracellular Ca2+ dynamics and activation of a calcium-activated non-selective cationic current. In this computational study, we show how intracellular calcium dynamics driven by synaptically triggered Ca2+ influx as well as Ca2+ release/uptake by the endoplasmic reticulum in conjunction with a calcium-activated non-selective cationic current can explain all of the key observations underlying the burstlet theory of respiratory rhythm generation. Thus, we provide a mechanistic basis to unify the experimental findings on rhythm generation and motor output recruitment in the preBötC.

Phrenic afferent activation modulates cardiorespiratory output in the adult rat

Phrenic afferents project to brainstem areas responsible for cardiorespiratory control and the mid-cervical spinal cord containing the phrenic motor nucleus. Our purpose was to quantify the impact of small and large diameter phrenic afferent activation on phrenic motor output. Anesthetized and ventilated rats received unilateral phrenic nerve stimulation while contralateral phrenic motor output and blood pressure were recorded. Twelve currents of 40Hz inspiratory-triggered stimulation were delivered (20 seconds on, 5 minutes off) to establish current response curves. Stimulation pulse width was varied to preferentially activate large diameter phrenic afferents (narrow pulse width) and recruit small diameter fibers (wide pulse width). Contralateral phrenic amplitude was elevated immediately post-stimulation at currents above 35 µA for wide, and 70 µA for narrow pulse stimulation when compared to animals not receiving stimulation (time controls). Wide pulse width stimulation also increased phrenic burst frequency at currents ≥35 µA, caused a transient decrease in mean arterial blood pressure at currents ≥50 µA, and resulted in a small change in heart rate at 300 µA. Unilateral dorsal rhizotomy attenuated stimulation-induced cardiorespiratory responses, indicating phrenic afferent activation is required. Additional analyses compared phrenic motor amplitude to output before stimulation and showed that episodic activation of phrenic afferents with narrow pulse stimulation can induce short-term plasticity. We conclude that activation of phrenic afferents: 1) enhances contralateral phrenic motor amplitude when large diameter afferents are activated, and 2) when small diameter fibers are recruited the amplitude response is associated with changes in burst frequency and cardiovascular parameters.

Neuromuscular Fatigue in Unimanual Handgrip Does Not Completely Affect Simultaneous Bimanual Handgrip

Simultaneous bimanual movements are not merely the sum of two unimanual movements. Here, we considered the unimanual/bimanual motor system as comprising three components: unimanual-specific, bimanual-specific, and overlapping (mobilized during both unimanual and bimanual movements). If the force-generating system controlling the same limb differs between unimanual and bimanual movements, unimanual exercise would be expected to fatigue the unimanual-specific and overlapping parts in the force-generating system but not the bimanual-specific part. Therefore, we predicted that the decrease in bimanual force generation induced by unimanual neuromuscular fatigue would be smaller than the decrease in unimanual force generation. Sixteen healthy right-handed adults performed unimanual and bimanual maximal handgrip measurements before and after a submaximal fatiguing handgrip task. In the fatigue task, participants were instructed to maintain unimanual handgrip force at 50% of their maximal handgrip force until the time to task failure. Each participant performed this task in a left-hand fatigue (LF) condition and a right-hand fatigue (RF) condition, in a random order. Although the degree of neuromuscular fatigue was comparable in both conditions, as expected, the decrease in bimanual right handgrip force was significantly smaller than those during unimanual right performance in the RF condition, but not in the LF condition. These results indicate that for the right-hand, neuromuscular fatigue in unimanual handgrip does not completely affect simultaneous bimanual handgrip. Regarding the underlying mechanisms, we propose that although neuromuscular fatigue caused by unimanual handgrip reduces the motor output of unimanual-specific and overlapping parts in the force-generating system, when simultaneous bimanual handgrip is performed, the overlapping part (which is partially fatigued) and the bimanual-specific part (which is not yet fatigued) generate motor output, thus decreasing the force reduction.

Methods and Strategies for Reconditioning Motor Output and Postural Balance in Frail Older Subjects Prone to Falls

In frail older subjects, the motor output of the antigravity muscles is fundamental in resisting falls. These muscles undergo accelerated involutions when they are inactive and the risk of falling increases during leisure and domestic physical activity. In order to reduce their risk of falling, frail older subjects limit their physical activities/exercises. The problem is that the less they exercise, the less they are able to exercise and the greater the risk in exercising. Hence, a vicious circle sets up and the antigravity muscles inevitably continue to deteriorate. This vicious circle must be broken by starting a reconditioning program based on developing the strength of antigravity muscles (especially lower-limb muscles). To begin with, for each increase in muscle strength, postural balance is improved. Once this increase reaches the threshold beyond which postural balance no longer improves, it seems appropriate to implement exercises aimed at concomitantly improving motor output and postural balance in order to counteract or even reverse the involution process of the postural balance system. Methods and strategies toward this end are proposed in this present communication. However, the transfer effects between strength increase and postural balance ability are not yet totally known and future research should evaluate the relationship between muscle strength and postural balance throughout rehabilitation programs (i.e., program follow-ups) in frail older subjects in order to advance knowledge of this relationship.

Distance estimation from monocular cues in an ethological visuomotor task

In natural contexts, sensory processing and motor output are closely coupled, which is reflected in the fact that many brain areas contain both sensory and movement signals. However, standard reductionist paradigms decouple sensory decisions from their natural motor consequences, and head-fixation prevents the natural sensory consequences of self-motion. In particular, movement through the environment provides a number of depth cues beyond stereo vision that are poorly understood. To study the integration of visual processing and motor output in a naturalistic task, we investigated distance estimation in freely moving mice. We found that mice use vision to accurately jump across a variable gap, thus directly coupling a visual computation to its corresponding ethological motor output. Monocular eyelid suture did not affect performance, thus mice can use cues that do not depend on binocular disparity and stereo vision. Under monocular conditions, mice performed more vertical head movements, consistent with the use of motion parallax cues, and optogenetic suppression of primary visual cortex impaired task performance. Together, these results show that mice can use monocular cues, relying on visual cortex, to accurately judge distance. Furthermore, this behavioral paradigm provides a foundation for studying how neural circuits convert sensory information into ethological motor output.

Calculation of transient temperature and rated capacity of three-phase induction motor under different working systems

This paper aims to propose a method to determine the temperature rise and rated capacity of induction motors under different working systems. A dynamic mathematical model, a 3D temperature field model, and finite element method are used to analyze the electromagnetic loss and transient temperature rise, respectively. The influence of the motor starting process on the temperature rise is taken into account, which resolves the complex loading of transient heat source. The maximum allowable running times for the motor operating with different overloads are determined. The relationship between the motor output power and the allowable running time is obtained, and it provides a basis to determine the rated capacity of motor under S2 working system. The relationship between the motor output power and the temperature rise under different load duration rates is also obtained and provides reasonable evidence to determine the rated capacity of the motor under S3-working system.

Prediction and action in cortical pain processing

Predicting that a stimulus is painful facilitates action to avoid harm. But does the prediction of upcoming painful events engage the same or different processes than acting to avoid or reduce current pain? In this fMRI experiment, we investigated brain activity as a function of current and predicted painful or nonpainful thermal stimulation, and the ability of voluntary action to affect the duration of the upcoming stimulation. Participants (n = 30) performed a task which involved the administration of a painful or nonpainful stimulus (S1), which predicted an immediately subsequent very painful or nonpainful stimulus (S2). Participants’ task was to press a response button within a short time window upon the presentation of a response cue during S1. On action-effective trials, pressing the button within the specified time window reduced the duration of the upcoming stimulation. On action-ineffective trials, pressing the button had no effect on upcoming stimulation. Predicted pain increased activation in regions including anterior cingulate cortex (ACC), midcingulate cortex (MCC), and insula; however, activation in ACC and MCC depended on whether a meaningful action was performed, with MCC activation showing a direct relationship with motor output. Region-of-interest analyses revealed that insula’s responses for predicted pain were also modulated by potential action consequences, especially in the left hemisphere, albeit without a direct relationship with motor output. Taken together, these findings suggest that cortical pain processing is not specifically tied to the sensory stimulus, but instead depends on the consequences of that stimulus for sensorimotor control of behavior.Significance statementDuring acute pain, the processing of an acute sensory event likely occurs in parallel with predictive processing about its relevance for current and upcoming voluntary behavior. Here, we temporally separated the functional processes underlying current and predicted pain and found that activation in regions typically implicated in acute pain is modulated both by the noxious nature of upcoming events, as well as by the possibility to affect those events via voluntary action. Specifically, activation in anterior cingulate cortex (ACC), midcingulate cortex (MCC), and insula during the delivery of a painful or nonpainful stimulus was modulated by whether an upcoming stimulus would be painful. Furthermore, ACC/MCC involvement in pain prediction depended on whether a meaningful action was performed, i.e., whether a button-press action would reduce the duration of the upcoming stimulus. Although insula activation was also affected by the possibility of the button-press action to reduce the duration of the upcoming stimulation, only MCC had a direct relationship with motor output.