scholarly journals Pre-synaptic inhibition of afferent feedback in the macaque spinal cord does not modulate with cycles of peripheral oscillations around 10 Hz

2014 ◽  
Author(s):  
Ferran Galán ◽  
Stuart N Baker
Keyword(s):  
Motor Output ◽  
Afferent Feedback ◽  
Feedback Gain ◽  
Synaptic Inhibition ◽  
Antidromic Activation ◽  
Stimulus Interval ◽  
Finger Flexion ◽  
Mean Width ◽  
Spinal Interneuron ◽  
Terminal Excitability

Spinal interneurons are partially phase-locked to physiological tremor around 10Hz. The phase of spinal interneuron activity is approximately opposite to descending drive to motoneurons, leading to partial phase cancellation and tremor reduction. Pre-synaptic inhibition of afferent feedback modulates during voluntary movements, but it is not known whether it tracks more rapid fluctuations in motor output such as during tremor. In this study, dorsal root potentials (DRPs) were recorded from the C8 and T1 roots in two macaque monkeys following intra-spinal micro-stimulation (random inter-stimulus interval 1.5-2.5 s, 30-100?A), whilst the animals performed an index finger flexion task which elicited peripheral oscillations around 10Hz. Forty one responses were identified with latency <5ms; these were narrow (mean width 0.59 ms), and likely resulted from antidromic activation of afferents following stimulation near terminals. Significant modulation during task performance occurred in 16/41 responses, reflecting terminal excitability changes generated by pre-synaptic inhibition (Wall?s excitability test). Stimuli falling during large-amplitude 8-12Hz oscillations in finger acceleration were extracted, and sub-averages of DRPs constructed for stimuli delivered at different oscillation phases. Although some apparent phase-dependent modulation was seen, this was not above the level expected by chance. We conclude that although terminal excitability reflecting pre-synaptic inhibition of afferents modulates over the timescale of a voluntary movement, it does not follow more rapid changes in motor output. This suggests that pre-synaptic inhibition is not part of the spinal systems for tremor reduction described previously, and that it plays a role in overall ? but not moment-by-moment ? regulation of feedback gain.

Human proprioceptive adaptations during states of height-induced fear and anxiety

2011 ◽  
Vol 106 (6) ◽  
pp. 3082-3090 ◽  
Author(s):  
Justin R. Davis ◽  
Brian C. Horslen ◽  
Kei Nishikawa ◽  
Katie Fukushima ◽  
Romeo Chua ◽  
...  
Keyword(s):  
Evoked Potentials ◽  
Somatosensory Cortex ◽  
Somatosensory Evoked Potentials ◽  
Emotional Experience ◽  
Afferent Feedback ◽  
Triceps Surae ◽  
Feedback Gain ◽  
Postural Threat ◽  
Fear And Anxiety ◽  
Stimulation Of

Clinical and experimental research has demonstrated that the emotional experience of fear and anxiety impairs postural stability in humans. The current study investigated whether changes in fear and anxiety can also modulate spinal stretch reflexes and the gain of afferent inputs to the primary somatosensory cortex. To do so, two separate experiments were performed on two separate groups of participants while they stood under conditions of low and high postural threat. In experiment 1, the proprioceptive system was probed using phasic mechanical stimulation of the Achilles tendon while simultaneously recording the ensuing tendon reflexes in the soleus muscle and cortical-evoked potentials over the somatosensory cortex during low and high threat conditions. In experiment 2, phasic electrical stimulation of the tibial nerve was used to examine the effect of postural threat on somatosensory evoked potentials. Results from experiment 1 demonstrated that soleus tendon reflex excitability was facilitated during states of height-induced fear and anxiety while the magnitude of the tendon-tap-evoked cortical potential was not significantly different between threat conditions. Results from experiment 2 demonstrated that the amplitudes of somatosensory-evoked potentials were also unchanged between threat conditions. The results support the hypothesis that muscle spindle sensitivity in the triceps surae muscles may be facilitated when humans stand under conditions of elevated postural threat, although the presumed increase in spindle sensitivity does not result in higher afferent feedback gain at the level of the somatosensory cortex.

The Central Nervous Control of Complex Movements in the Uropods of Crayfish

1969 ◽  
Vol 51 (1) ◽  
pp. 135-150
Author(s):  
J. L. LARIMER ◽  
D. KENNEDY
Keyword(s):  
Central Element ◽  
Simultaneous Recording ◽  
Motor Output ◽  
Afferent Feedback ◽  
Rhythmic Pattern ◽  
Nervous Control ◽  
Motor Pathways ◽  
Combined Movements ◽  
Motor Neurones ◽  
Two Sides

1. The control of postural uropod muscles in the crayfish has been investigated by stimulating ‘command’ interneurones isolated from central connectives. Reciprocity is preserved between exciters and inhibitors innervating the same muscle, and between motor axons serving antagonists. 2. The control of combined movements, involving groups of muscles that are neither synergists nor antagonists, was analysed by simultaneous recording. Most command fibres affected several different motor pathways, and different command fibres produced different combinations of output. It is concluded that quite complex movements may be encoded in the connexions of a single central element. 3. In several instances it was shown unequivocally that single central neurones were responsible for releasing the motor output. One identified command neurone produces a stereotyped, rhythmic pattern of activity in several motor pathways. This effect did not depend upon afferent feedback for its form or frequency. 4. Command interneurones often produce asymmetrical responses in the appendages of the two sides. Some of these make connexions only to the ipsilateral motor neurones, others only to contralateral ones, and most make differential connexions on the two sides.

scholarly journals An In Vitro Spinal Cord–Hindlimb Preparation for Studying Behaviorally Relevant Rat Locomotor Function

2009 ◽  
Vol 101 (2) ◽  
pp. 1114-1122 ◽  
Author(s):  
Heather Brant Hayes ◽  
Young-Hui Chang ◽  
Shawn Hochman
Keyword(s):  
Spinal Cord ◽  
Sensory Feedback ◽  
Muscle Activation ◽  
Motor Pattern ◽  
Motor Output ◽  
Afferent Feedback ◽  
Neonatal Rat ◽  
Stride Frequency ◽  
Muscle Activation Patterns

Although the spinal cord contains the pattern-generating circuitry for producing locomotion, sensory feedback reinforces and refines the spatiotemporal features of motor output to match environmental demands. In vitro preparations, such as the isolated rodent spinal cord, offer many advantages for investigating locomotor circuitry, but they lack the natural afferent feedback provided by ongoing locomotor movements. We developed a novel preparation consisting of an isolated in vitro neonatal rat spinal cord oriented dorsal-up with intact hindlimbs free to step on a custom-built treadmill. This preparation combines the neural accessibility of in vitro preparations with the modulatory influence of sensory feedback from physiological hindlimb movement. Locomotion induced by N-methyl d-aspartate and serotonin showed kinematics similar to that of normal adult rat locomotion. Changing orientation and ground interaction (dorsal-up locomotion vs ventral-up air-stepping) resulted in significant kinematic and electromyographic changes that were comparable to those reported under similar mechanical conditions in vivo. We then used two mechanosensory perturbations to demonstrate the influence of sensory feedback on in vitro motor output patterns. First, swing assistive forces induced more regular, robust muscle activation patterns. Second, altering treadmill speed induced corresponding changes in stride frequency, confirming that changes in sensory feedback can alter stride timing in vitro. In summary, intact hindlimbs in vitro can generate behaviorally appropriate locomotor kinematics and responses to sensory perturbations. Future studies combining the neural and chemical accessibility of the in vitro spinal cord with the influence of behaviorally appropriate hindlimb movements will provide further insight into the operation of spinal motor pattern-generating circuits.

scholarly journals Coherence Between Motor Cortical Activity and Peripheral Discontinuities During Slow Finger Movements

2009 ◽  
Vol 102 (2) ◽  
pp. 1296-1309 ◽  
Author(s):  
Elizabeth R. Williams ◽  
Demetris S. Soteropoulos ◽  
Stuart N. Baker
Keyword(s):  
Primary Motor Cortex ◽  
Phase Relationship ◽  
Conduction Delay ◽  
Finger Movements ◽  
Antidromic Activation ◽  
Spike Triggered Averaging ◽  
Finger Flexion ◽  
Flexion Extension ◽  
Corticomotoneuronal Cells ◽  
Flexion And Extension

Slow finger movements in man are not smooth, but are characterized by 8- to 12-Hz discontinuities in finger acceleration thought to have a central source. We trained two macaque monkeys to track a moving target by performing index finger flexion/extension movements and recorded local field potentials (LFPs) and spike activity from the primary motor cortex (M1); some cells were identified as pyramidal tract neurons by antidromic activation or as corticomotoneuronal cells by spike-triggered averaging. There was significant coherence between finger acceleration in the approximately 10-Hz range and both LFPs and spikes. LFP–acceleration coherence was similar for flexion and extension movements (0.094 at 9.8 Hz and 0.11 at 6.8 Hz, respectively), but substantially smaller during steady holding (0.0067 at 9.35 Hz). The coherence phase showed a significant linear relationship with frequency over the 6- to 13-Hz range, as expected for a constant conduction delay, but the slope indicated that LFP lagged acceleration by 18 ± 14 or 36 ± 8 ms for flexion and extension movements, respectively. Directed coherence analysis supported the conclusion that the dominant interaction was in the acceleration to LFP (i.e., sensory) direction. The phase relationships between finger acceleration and both LFPs and spikes shifted by about π radians in flexion compared with extension trials. However, for a given trial type the phase relationship with acceleration was similar for cells that increased their firing during flexion or during extension trials. We conclude that movement discontinuities during slow finger movements arise from a reciprocally coupled network, which includes M1 and the periphery.

γ-Aminobutyric acid and primary afferent depolarization in feline spinal cord

1979 ◽  
Vol 57 (10) ◽  
pp. 1157-1167 ◽  
Author(s):  
B. R. Sastry
Keyword(s):  
Spinal Cord ◽  
Nerve Stimulation ◽  
Muscle Afferents ◽  
Aminobutyric Acid ◽  
Primary Afferent Depolarization ◽  
Antidromic Activation ◽  
Primary Afferent ◽  
Afferent Terminal ◽  
Group I ◽  
Terminal Excitability

The effects of iontophoretically applied γ-aminobutyric acid (GABA), (−)-nipecotic acid (NCA), 2,4-diaminobutyric acid (DABA), and pentobarbital were examined on the thresholds for antidromic activation of single group I muscle afferents, in decerebrated spinal cats. GABA decreased the threshold for antidromic activation of the majority of the afferents. During this decrease in the threshold, the preterminal axons were depolarized. This depolarization was decreased by a prior depolarization, but increased by a hyperpolarization, of the afferent. During the depolarization of the afferent produced by GABA, the size of the orthodromic action potential was decreased. Iontophoretically applied bicuculline antagonized the effect of GABA on the threshold for antidromic activation of the afferents. NCA, DABA, and pentobarbital potentiated the action of GABA on the afferent terminal excitability. Pre-treatment of the animals with semicarbazide, which reportedly depletes spinal GABA, resulted in a reduction in the threshold produced by a conditioning stimulation of other group I afferents. GABA decreased the threshold for antidromic activation of the nonterminal regions of the afferents when applied near the stimulation sites. The amounts of GABA required to produce a decrease in the threshold of the nonterminal afferents were greater than those required to produce a comparable effect on the terminal regions of the fibres. Iontophoretically applied NCA and bicuculline, in amounts that were adequate to alter the effects of applied GABA, failed to affect the nerve stimulation-induced decrease in the threshold for antidromic activation of the fibres. Intravenously injected bicuculline, however, antagonized the actions of GABA as well as of the reduction in the threshold produced by nerve stimulation.These results indicate that (1) GABA-induced increase in the excitability of group I afferent terminals is associated with a depolarization of the afferent, (2) the uptake of iontophoretically applied amino acid into the spinal cord tissue appears to limit its action on the afferent terminal excitability, (3) GABA has a preterminal depolarizing action on group I muscle afferents, and (4) primary afferent depolarization produced by nerve stimulation may be of diffuse origin and, hence, cannot be significantly affected by iontophoretically applied NCA and bicuculline.

Slow Wave Activity Related to Working Memory Maintenance in the N-Back Task

2016 ◽  
Vol 30 (4) ◽  
pp. 141-154 ◽  
Author(s):  
Kira Bailey ◽  
Gregory Mlynarczyk ◽  
Robert West
Keyword(s):  
Working Memory ◽  
Slow Wave ◽  
Time Course ◽  
Relevant Information ◽  
Wave Activity ◽  
Slow Wave Activity ◽  
Response Accuracy ◽  
Functional Neuroanatomy ◽  
Stimulus Interval ◽  
Back Task

Abstract. Working memory supports our ability to maintain goal-relevant information that guides cognition in the face of distraction or competing tasks. The N-back task has been widely used in cognitive neuroscience to examine the functional neuroanatomy of working memory. Fewer studies have capitalized on the temporal resolution of event-related brain potentials (ERPs) to examine the time course of neural activity in the N-back task. The primary goal of the current study was to characterize slow wave activity observed in the response-to-stimulus interval in the N-back task that may be related to maintenance of information between trials in the task. In three experiments, we examined the effects of N-back load, interference, and response accuracy on the amplitude of the P3b following stimulus onset and slow wave activity elicited in the response-to-stimulus interval. Consistent with previous research, the amplitude of the P3b decreased as N-back load increased. Slow wave activity over the frontal and posterior regions of the scalp was sensitive to N-back load and was insensitive to interference or response accuracy. Together these findings lead to the suggestion that slow wave activity observed in the response-to-stimulus interval is related to the maintenance of information between trials in the 1-back task.

Behavior in the Brain

2010 ◽  
Vol 24 (2) ◽  
pp. 76-82 ◽  
Author(s):  
Martin M. Monti ◽  
Adrian M. Owen
Keyword(s):  
Motor Behavior ◽  
Functional Neuroimaging ◽  
Brain Activity ◽  
Motor Output ◽  
The Unconscious ◽  
Ethical Implications ◽  
Brain Responses ◽  
Minimally Conscious ◽  
Brain Insults ◽  
Brain Behavior

Recent evidence has suggested that functional neuroimaging may play a crucial role in assessing residual cognition and awareness in brain injury survivors. In particular, brain insults that compromise the patient’s ability to produce motor output may render standard clinical testing ineffective. Indeed, if patients were aware but unable to signal so via motor behavior, they would be impossible to distinguish, at the bedside, from vegetative patients. Considering the alarming rate with which minimally conscious patients are misdiagnosed as vegetative, and the severe medical, legal, and ethical implications of such decisions, novel tools are urgently required to complement current clinical-assessment protocols. Functional neuroimaging may be particularly suited to this aim by providing a window on brain function without requiring patients to produce any motor output. Specifically, the possibility of detecting signs of willful behavior by directly observing brain activity (i.e., “brain behavior”), rather than motoric output, allows this approach to reach beyond what is observable at the bedside with standard clinical assessments. In addition, several neuroimaging studies have already highlighted neuroimaging protocols that can distinguish automatic brain responses from willful brain activity, making it possible to employ willful brain activations as an index of awareness. Certainly, neuroimaging in patient populations faces some theoretical and experimental difficulties, but willful, task-dependent, brain activation may be the only way to discriminate the conscious, but immobile, patient from the unconscious one.

Finger flexion contrasted to extension activates higher-order motor circuitry

2005 ◽  
Vol 25 (1_suppl) ◽  
pp. S358-S358
Author(s):  
M W Stenekes ◽  
J M Hoogduin ◽  
Th Mulder ◽  
J H B Geertzen ◽  
K L Leenders ◽  
...  
Keyword(s):  
Higher Order ◽  
Finger Flexion
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