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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.

High-frequency rTMS combined with gait training improves lower extremity motor score (LEMS) and gait velocity in SCI subjects who are able to walk over ground. The aim of this study was to optimize the functional outcome in early phases of gait rehabilitation in SCI using rTMS as an additional treatment to physical therapy. The present study included 31 motor incomplete SCI subjects randomized to receive real or sham rTMS, just before Lokomat gait training (15 subjects for real, 16 for sham rTMS). rTMS consisted of one daily session for 20 days over vertex (at 20 Hz). The subjects were evaluated using modified Ashworth scale (MAS) for spasticity, upper and lower extremity motor score (UEMS and LEMS, respectively), ten meters walking test (10MWT) and Walking Index for SCI (WISCI-II) for gait at baseline, after last rTMS session, and during follow-up. UEMS and LEMS improved significantly after last session in both groups and during follow-up period. The improvement was greater in real than in sham rTMS group. At follow-up, 71.4 % of the subjects after real rTMS and 40 % of the subjects after sham rTMS could perform 10MWT without significant differences in gait velocity, cadence, step length and WISCI-II between both groups. We conclude that 20 sessions of daily high-frequency rTMS combined with Lokomat gait training can lead to clinical improvement of gait in motor incomplete SCI. Such combined treatment improved motor strength in lower extremity in incomplete SCI subjects and in upper extremity in those with cervical SCI.

Imagining motor actions is enough to enhance cortical motor excitability. However, the fact that execution of the motor task has to be inhibited should have a correlate on the extent of cortical excitability enhancement. Therefore, we examined the possible differences between real and motor imagery of simple reaction time tasks (SRT) in the facilitation of the motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS) and in the reduction of short-interval intracortical inhibition (SICI) taking place before the movement onset. Thirteen healthy volunteers were requested to perform visual real or imaginary SRT tasks (rSRT and iSRT) with their dominant hand. For rSRT, subjects had to perform a rapid isometric squeeze as soon as possible after the imperative signal. For iSRT they had to imagine the same movement without actually doing it. Electromyographic (EMG) signals were recorded from the first dorsal interosseus (FDI) muscle. The mean EMG onset was calculated for each subject in rSRT trials. Single-and paired-pulse TMS (at an interstimulus interval of 2.5 ms) were applied at rest and at time intervals of -25, -50, -75, -100 and -125 ms before the expected real (rSRT) mean EMG onset. In rSRT there was a significant increase of MEP to single-pulseTMS at the intervals of -50 and -25 ms, and in iSRT at -50 ms in comparison to the rest condition. % SICI changes were significantly reduced at the intervals of -75, -50 and -25 ms, before EMG the onset in rSRT and at -50 and -25 in iSRT (P < 0.05) in comparison to % SICI changes at rest. The differences between MEPs to spTMS and MEP to ppTMS were significantly larger at rest, -125 and -100 ms intervals in rSRT, and at all intervals in iSRT. Imagining to move causes an increase in corticospinal excitability and a decrease in intracortical inhibition that follow a temporal profile similar to those observed with real movements. However, complete removal of SICI happened only in rSRT at the shortest intervals before the EMG onset. Such action may delineate new tool in motor rehabilitation of patients who have limitation to move.

The startle reaction (SR) is usually understood as an involuntary reaction to an unexpected sensory input. However, there is evidence that the mechanisms involved in the SR contribute also to the execution of actions that we consider voluntary. We need to exert a fine control of the motor output, which usually involves inhibition of the reflex reaction but it may also imply letting the SR manifest, shaped in accordance with our willed actions. The latter occurs mainly with relatively simple ballistic movements but it has also been shown to occur in complex movements. In this review, we describe arguments published in the literature in favour of the contribution of subcortical motor tracts involved in the generation of the SR to the execution of voluntary movements. Some of these studies have brought insight on the mechanisms accounting for motor preparation and execution of voluntary movements.

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.

The control of eye movements depends in part on subcortical motor centres. Gaze is often directed towards salient visual stimuli of our environment with no conscious voluntary commands. To further understand to what extent preprogrammed eye movements can be triggered subcortically, we carried out a study in normal volunteers to examine the effects of a startling auditory stimulus (SAS) on externally guided saccades. A peripheral visual cue was presented in the horizontal plane at a site distant 15 degrees from the fixation point, and subjects were instructed to make a saccade to it. SAS was presented together with the peripheral visual cue in 20% of trials. To force rapid visual fixation at the end of the saccade, targets were loaded with a second cue, a small arrow pointing towards the right or the left (or a neutral sign), not distinguishable with peripheral vision. Subjects were requested to perform a flexion/extension wrist movement, according to the direction of the arrow (or not to move if the second cue was the neutral sign). SAS presented together with the visual target caused a significant shortening of the latency of saccadic movements. The wrist movements performed as a response to the second cue had similar reaction times regardless of whether the trial contained a SAS or not. Our results show that voluntary saccades to peripheral targets are speeded up by activation of the startle circuit, and that this effect does not cause a significant disturbance in the execution of simple in-target cues. These results suggest that subcortical structures play a main role in preparation of externally guided saccades.

Studies with transcranial electrical or magnetic stimulation have shown a progressive increase of motor cortex excitability beginning at about 80 ms before the onset of electromyographic (EMG) activity in a voluntary movement. We studied whether a similar increase in excitability occurs in subcortical motor tracts before execution of a ballistic movement. In ten healthy volunteers, we examined the effects of a startling auditory stimulus (SAS) applied at various intervals following the imperative signal (IS) in a reaction time task experiment. We hypothesized that, if the excitability of the reticulospinal tract increases before onset of muscle activity, there would be a corresponding change in the size of the startle response elicited either in muscles responding to the SAS, the orbicularis oculi (OOc) and sternocleidomastoid (SCM), or in the agonist muscle for the reaction. A SAS was applied at intervals of 0, 20, 40, 60, 80, and 100 ms after IS in a reaction time task paradigm in which subjects had to perform a ballistic movement of wrist flexion. We measured the size of the EMG bursts recorded in the OOc and the SCM, as well as the size of the first EMG burst in the wrist flexors (WF). Comparisons were done with data obtained in baseline trials, in which unexpected SAS of the same intensity were delivered without preparation, and control trials, in which subjects performed the same motor task with no SAS. The size of the averaged OOc, SCM, and WF were larger in trials with SAS than in baseline or control trials, with significant differences in the SCM and in the WF (p<0.05). However, there were no effects of time interval on the size of OOc, SCM, or WF (p>0.05). These results indicate that, in the execution of a ballistic movement, the excitability of the subcortical motor tracts activated by a SAS is similarly enhanced at the time of the IS and 100 ms afterwards, just before the onset of EMG activity. We conclude that, in contrast with the reported progressive increase of excitability in the corticospinal tract, the excitability of the tracts activated by a SAS do not change between the IS and the onset of EMG activity.

A startling auditory stimulus delivered during preparation for execution of a ballistic movement in a simple reaction time task experiment induces two effects: a startle response and a reaction time shortening (the StartReact effect). We investigated whether prepulse inhibition of the startle response is effective in suppressing either one of these effects during motor preparation. Twelve healthy volunteers were presented with seven different experimental conditions in random order: while at rest, subjects received a low intensity electrical shock on the middle finger of the left hand (Prep), a loud auditory stimulus (Start), or a combination of these two (PrepStart). While engaged in preparation for a visual simple reaction time task, they were presented with the imperative signal for execution of the reaction (React), or with any of the combinations PrepReact, StartReact, or PrepStartReact. We recorded the EMG activity from the orbicularis oculi and the sternocleidomastoid muscles to assess the startle response, and from the wrist extensor muscles to assess reaction time. The startle response was markedly reduced when Prep was presented 100 ms before Start regardless of whether the subjects were at rest or preparing for the reaction. Reaction time shortened significantly in StartReact trials with respect to React trials, and the percentage shortening was not different in trials in which Prep preceded StartReact and inhibited the startle response. The fact that prepulse inhibition of the startle response is not accompanied by modification of the StartReact effect indicates that there are separate physiological mechanisms for the two effects, an observation that has implications for further understanding of the processes underlying motor preparation for a ballistic reaction.