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The effect of Jendrassik Maneuver (JM) has been extensively studied on monosynaptic reflexes in numerous muscles below the level at which the maneuver was performed. Here we hypothesize that the effect of JM could be observed also on other reflexes, indicating a widespread influence of performing a motor act such as the JM. We examined polysynaptic reflexes caudal (i.e., the withdrawal reflex of the lower extremities) and rostral (i.e., the blink reflex to supraorbital nerve stimulation) to the level of JM contraction. We have assessed soleus tendon (T) reflex; withdrawal reflex in tibialis anterior and soleus muscle; blink reflex (BR), blink reflex excitability recovery curve (BR-ER) and prepulse inhibition of the blink reflex. Our results showed that (1) T-reflex amplitude increased during JM and decreased just after and 15 min after JM; (2) no change in the withdrawal reflex; (3) R2 area of BR reduced significantly just after or 15 min after JM; (4) Prepulse inhibition in BR reduced significantly during JM; (5) no change in BR-ER. Our results indicate that JM leads to generalized effects on neural excitability at both caudal and rostral levels. Furthermore, JM has a selective effect on excitability of reflex circuitries.

Introduction: Changes in spinal reflexes can result from alterations in the spinal cord and descending pathways. We studied whether H-reflex excitability and its recovery depend on the level and/or severity of spinal cord injury (SCI)., Methods: The soleus Hmax and Mmax responses and the H-reflex recovery curve (HRC) at interstimulus intervals (ISIs) ranging from 50 to 1,000 ms were recorded in 38 SCI individuals and 18 healthy subjects., Results: Amplitude of Mmax correlated with level and severity of lesion (smaller amplitude correlated with more severe SCI or with more caudal lesion). Hmax/Mmax correlated only with age in the SCI group. HRC was increased significantly in complete SCI at ISIs < 500 ms and in incomplete SCI at ISIs > 200 ms with respect to healthy subjects., Conclusions: The changes in spinal reflexes as measured by the H-reflex and its recovery curve after SCI depend on the severity, but not on the level of the lesion., (© 2015 Wiley Periodicals, Inc.)

Objective: Intrathecal baclofen (ITB) is an efficient treatment modality for severe spasticity that is considered to act at the spinal level. Its influence on phasic spasticity is usually determined clinically by testing muscle reflexes, and on tonic spasticity by using scores such as the Modified Ashworth Scale (MAS). Neurophysiological techniques, e.g., soleus H reflex, may provide additional information regarding ITB efficacy. There is, however, only scarce information available on time-response relationships of clinical and neurophysiological measures of spasticity obtained at different levels along the neuroaxis., Methods: Fourteen patients with severe spastic paraparesis underwent serial evaluation of MAS in upper and lower limbs and serial testing of H reflex in soleus and flexor carpi radialis muscles, T wave in quadriceps and biceps brachii muscles, and blink reflex (BR) with and without prepulse, at baseline, and 15, 30, 60, 90, 120, and 180 min following ITB bolus application., Results: ITB bolus application caused significant suppression of soleus H reflex after 15 min and of quadriceps T wave after 30 min, while MAS dropped significantly after 60 min together with significant suppression of BR R2 area without and with prepulse stimulation. H reflex in flexor carpi radialis and T wave in biceps brachii were not significantly suppressed by ITB. The time course of early changes in soleus H(max)/M(max) ratio and quadriceps T wave indicates a suppression of hyperreflexia at the spinal level, while a later reduction of MAS synchronously with suppression of BR with and without prepulse concurs with a brainstem effect of ITB., Conclusion: Temporal concurrence between suppression of brainstem reflexes and desired suppression of lower limb muscle hypertonia after ITB bolus application suggests that both may be at least partially mediated from a common CNS region of activity., Significance: Our data concur with a significant brainstem action of ITB., (Copyright © 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: Spasticity is common after spinal cord injury (SCI). Exaggerated tendon jerks, clonus, and spasms are key features of spasticity that result from hyperexcitability of the stretch reflex circuit. Here we studied the effects of vibration on the rectus femoris muscle (RF) on clinical and electrophysiological measures of spasticity in the leg., Methods: Nineteen SCI patients with spasticity and nine healthy subjects were studied at baseline and under stimulation (vibration at 50 Hz during 10 min on the thigh). Neurophysiological studies included evaluation of the soleus T wave and Hmax/Mmax ratio. Clinical measurements of spasticity were the score in the Modified Ashworth Scale (MAS), range of motion (ROM), and duration and frequency of clonus., Results: Patients with incomplete SCI (iSCI) presented higher number of cycles and longer duration of clonus than patients with complete SCI (cSCI). The Hmax/Mmax ratio and T wave amplitude at baseline were significantly larger in iSCI patients than in cSCI or healthy subjects. During vibration, we found a significant reduction of MAS and duration of clonus, and an increase in ROM, in all patients as a group. The Hmax/Mmax ratio and the T wave amplitude decreased significantly in both, patients and controls., Conclusions: Prolonged vibration on proximal lower extremity muscles decreased limb spasticity in patients with spinal cord injury, regardless of whether the lesion is complete or incomplete., Significance: Muscle vibration may be useful for physical therapy, by facilitating passive and active movements of the extremities in spastic SCI patients., (Copyright © 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: Noxious digital nerve stimulation leads to transient suppression of the electromyographic activity in isometrically contracted hand muscles, known as the "cutaneous silent period" (CSP). To date, neurotransmitters potentially involved in mediating this electromyographic (EMG) suppression remain unknown. Anecdotal observation lead to the hypothesis that antihistaminic medication may counteract nociceptive EMG suppression, as CSPs in one male subject who was accustomed to CSP recordings were temporarily lost following ingestion of an antihistaminic drug for acute rhinitis. A second otherwise healthy male subject, who was on long-term cetirizine for allergic rhinitis, presented without clearly defined CSPs when volunteering for normal values., Methods: We undertook a systematic study in five healthy subjects (including the one with temporarily lost CSPs) who underwent serial CSP testing after ingestion of 10 mg cetirizine. CSPs were elicited in thenar muscles following digit II and digit V stimulation (20 times sensory threshold, 100 sweeps rectified and averaged) before and 90, 180, and 360 min following intake of medication., Results: CSP onset latency, CSP end latency and CSP duration, as well as the index of suppression did not change significantly following ingestion of 10 mg cetirizine. Repeat study in the subject with no clearly defined CSPs on long-term treatment revealed persistently absent CSPs after a 5-week withdrawal from cetirizine., Conclusion: CSPs are not affected by therapeutic doses of the H1 antihistaminic cetirizine., Significance: Our findings suggest that histamine plays no major role as a neurotransmitter of CSPs.

Objective: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-delta fibers. The amount of muscle contraction has been reported to influence CSPs, but this has not been confirmed in studies applying clinically feasible stimulus parameters., Methods: Fourteen healthy subjects underwent comparison of CSPs while contracting the target muscle at different levels ranging from 10% to 50% of the maximum force, which was continuously monitored with a force transducer. Rectified surface electromyographic (EMG) recordings were obtained from abductor pollicis brevis muscle following ipsilateral recurrent noxious digit 2 and digit 5 stimulation., Results: Group average CSP onset and end latency, CSP duration, and the magnitude of EMG suppression were not influenced by volitional muscle contraction ranging from 10% to 50% of the maximum. In contrast, background EMG levels increased significantly with the amount of muscle force., Conclusions: CSPs prove to be robust nociceptive cutaneomuscular reflexes, which are - in contrast to previous reports - not significantly influenced by clinically easily applicable amounts of muscle force., Significance: Non-dependence on the amount of volitional target muscle activation over a range from 10% to 50% of individual maximum force levels renders CSPs particularly suitable for clinical use in patients with peripheral and spinal disorders affecting the A-delta fiber system.

Performing unlearned unimanual tasks when simultaneously carrying out another task with the contralateral hand is known to be difficult. The dual task interference theory predicts that reaction time will be delayed if the investigated task is performed in the course of ongoing contralateral movements. Ballistic movements can be performed at maximal speed in simple reaction time (SRT) experiments when subjects have adequately prepared the motor system needed for movement execution. When fully prepared, activation of subcortical motor pathways by a startling auditory stimulus (SAS) triggers the whole reaction. In this study, we have examined dual task interference with reaction time in eight healthy volunteers. They were presented with a visual imperative signal to perform unilateral SRT either in a baseline condition (control trials) or while carrying out contralateral rhythmic oscillatory movements (test trials). A SAS was introduced in 25% of the trials in both conditions. SRT was significantly delayed in the interference test trial when compared to control trials either with or without SAS (P<0.001). Control and test trials with SAS were significantly faster than those without SAS in both conditions (P<0.001). However, there were no significant differences in the percentage SRT shortening induced by SAS or in the percentage SRT delay observed in the test trials. Our results suggest that performing rhythmic oscillatory movements with one limb slows SRT in the contralateral limb and that this effect is likely related to motor preparation changes. The effect described here can be of interest for physiological studies of interlimb coordination and the mechanisms underlying the dual task interference phenomenon.

Objective: We aimed at characterizing the silent period induced in hand muscles by subcortical stimulation through electrodes implanted on the subthalamic nucleus for deep brain stimulation (STN-DBS)., Methods: In 10 patients with Parkinson's disease, we analyzed the inhibitory effects induced in the contralateral and ipsilateral thenar muscles by STN-DBS of varying stimulus intensity and strength of muscle contraction., Results: Both, the contralateral silent period (CSP) and the ipsilateral silent period (ISP) were induced by stimuli at an intensity subthreshold for eliciting a contralateral motor evoked potential (MEP) and were composed of two phases. With a stimulus intensity of 120% of active threshold and a strength of 20%, the first CSP had a mean onset latency of 38.0 +/- 2.9 ms and a mean duration of 37.7 ms +/- 2.8 ms, and the second CSP had a mean onset latency of 90.6 +/- 18.5 ms and a mean duration of 53.4 +/- 6.3 ms. The first ISP had a mean onset latency of 34.9 +/- 4.3 ms and a mean duration of 12.5 +/- 3.4 ms, and the second ISP had a mean onset latency of 76.3 +/- 10.1 ms and a mean duration of 23.1 +/- 9.0 ms. The duration of both phases of the CSP increased with increasing the stimulus intensity and the burst separating the two phases of the CSP increased in size with increasing the strength of muscle contraction or the stimulus intensity. No ipsilateral MEP was observed in any patient at any strength or stimulus intensity., Conclusion: Our results indicate that the silent period induced by STN-DBS has specific physiological mechanisms that differ from those of the silent period induced by cortical transcranial magnetic stimulation., Significance: The induction of ISP by stimulation of the motor tract at a point caudal to the corpus callosum indicates that non-callosal pathways are capable of generating ISP.