Journal of neurophysiology
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Randomized Controlled Trial
Neurophysiological correlates of nociceptive heterosynaptic long-term potentiation in humans.
Long-term potentiation (LTP) is a cellular model of synaptic plasticity and reflects an increase of synaptic strength. LTP is also present in the nociceptive system and is believed to be one of the key mechanisms involved in the manifestations of chronic pain. LTP manifested as an increased response in pain perception can be induced in humans using high-frequency electrical stimulation (HFS). ⋯ Conditioning HFS resulted in significant heterotopic effects after 30 min, including increased perceived intensity in response to (pinprick) mechanical and paired nonpainful electrical stimulation compared with control. The paired nonpainful electrical stimuli were accompanied by significantly enhanced responses regarding the ERP N1-P2 peak-to-peak and P300 amplitude compared with control. These findings suggest that HFS is capable of producing heterosynaptic spinal LTP that can be measured not only behaviorally but also using ERPs.
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Randomized Controlled Trial
Dyspnea as a noxious sensation: inspiratory threshold loading may trigger diffuse noxious inhibitory controls in humans.
Dyspnea, a leading respiratory symptom, shares many clinical, physiological, and psychological features with pain. Both activate similar brain areas. The neural mechanisms of dyspnea are less well described than those of pain. ⋯ The myotatic H-reflex was not inhibited by inspiratory loading, arguing against postsynaptic alpha motoneuron inhibition. Dyspnea, like pain, thus induced counterirritation, possibly indicating a C-fiber stimulation and activation of diffuse noxious inhibitory descending controls known to project onto spinal dorsal horn wide dynamic range neurons. This confirms the noxious nature of certain types of breathlessness, thus opening new physiological and perhaps therapeutic perspectives.
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Randomized Controlled Trial Clinical Trial
Spatio-temporal separation of roll and pitch balance-correcting commands in humans.
This study was designed to provide evidence for the hypothesis that human balance corrections in response to pitch perturbations are controlled by muscle action mainly about the ankle and knee joints, whereas balance corrections for roll perturbations are controlled predominantly by motion about the hip and lumbro-sacral joints. A dual-axis rotating support surface delivered unexpected random perturbations to the stance of 19 healthy young adults through eight different directions in the pitch and the roll planes and three delays between pitch and roll directions. Roll delays with respect to pitch were no delay, a short 50-ms delay of roll with respect to pitch movements, (chosen to correspond to the onset time of leg muscle stretch reflexes), and a long 150-ms delay between roll and pitch movements (chosen to shift the time when trunk roll velocity peaks to the time when trunk peak pitch velocity normally occurs). ⋯ Lower leg and trunk muscle activity appears to have a dual action in balance corrections. In trunk muscles the main action is to correct for roll perturbations and the lesser action may be an anticipatory stabilizing reaction for pitch perturbations. Likewise, the small changes in lower leg muscle activity may result from a generalized stabilizing reaction to roll perturbations, but the main action is to correct for pitch perturbations.
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Randomized Controlled Trial Clinical Trial
Human express saccade makers are impaired at suppressing visually evoked saccades.
1. We report the oculomotor behavior of human subjects who produce unusually high numbers (> 30%) of express saccades (latency range 85-135 ms) in the overlap saccade task, where express saccades are usually absent or small in number (< 15%). We refer to these subjects as "express saccade makers" (ES makers). 2. ⋯ The collicular fixation neurons are probably the final common pathway in the control of active fixation, and are in mutual inhibitory relationship with the saccade cells. 6. The decreased saccadic control observed in the ES makers suggests that saccade execution in humans is also gated by a fixation system. These ES makers may have reduced voluntarily control over saccade generation as a result of a defect or poor development of their fixation system.
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Randomized Controlled Trial Clinical Trial
Influence of instruction, prediction, and afferent sensory information on the postural organization of step initiation.
1. Our previous study showed that two distinct postural modifications occurred when subjects were instructed to step, rather than maintain stance, in response to a backward surface translation: 1) the automatic postural responses to the surfaces perturbation were reduced in magnitude and 2) the anticipatory postural adjustments promoting foot-off were shortened in duration. This study investigates the extent to which task instruction, prediction of perturbation velocity, and afferent sensory information related to perturbation velocity are responsible for these postural modification. 2. ⋯ We conclude that the CNS uses prediction of perturbation velocity to modify the excitability of early automatic postural responses when the postural goal changes. In contrast, actual afferent velocity information can be used to modify the duration of the anticipatory postural adjustments for a voluntary step in response to perturbation. Thus the CNS utilizes feed-forward prediction to modify peripherally triggered postural responses, and utilizes immediate afferent information to modify the centrally initiated postural adjustments associated with voluntary movement.