Influence of peripheral magnetic stimulation of soleus muscle on H and M waves.

[Purpose] This study evaluated the effects of repetitive peripheral magnetic stimulation of the soleus muscle on spinal cord and peripheral motor nerve excitability. [Subjects and Methods] Twelve healthy adults (mean age 22 years) who provided written informed consent were administered repetitive peripheral magnetic stimulation for 10 min. Pre-and post-stimulation latencies and amplitudes of H- and M-waves of the soleus muscle were measured using electromyography and compared using paired t-tests. [Results] Pre- and post-stimulation latencies (28.3 ± 3.3 vs. 29.1 ± 1.3 ms, respectively) and amplitudes (35.8 ± 1.3 vs. 35.8 ± 1.1 mV, respectively) of H-waves were similar. Pre-stimulation latencies of M-waves were significantly higher than post-stimulation latencies (6.1 ± 2.2 vs. 5.0 ± 0.9 ms, respectively), although pre- and post-stimulation amplitudes were similar (12.2 ± 1.4 vs. 12.2 ± 1.3 mV, respectively). Motor neuron excitability, based on the excitability of motor nerves and peripheral nerve action, was increased by M-waves following magnetic stimulation. [Conclusion] The lack of effect of magnetic stimulation on the amplitude and latency of the H-reflex suggests that magnetic stimulation did not activate sensory nerve synapses of α motor neurons in the spinal cord. However, because motor nerves were stimulated together with sensory nerves, the increased H-wave amplitude may have reflected changes in peripheral rather than in α motor nerves.

Prevalence of Genu Recurvatum during Walking and Associated Knee Pain in Chronic Hemiplegic Stroke Patients: A Preliminary Survey.

BACKGROUND: Although genu recurvatum during walking is a well-known issue in stroke rehabilitation, there are no reliable epidemiological data on its prevalence. The aim of the study was to investigate the prevalence of genu recurvatum during walking and associated knee pain among ambulatory community-dwelling patients with chronic hemiplegic stroke. METHODS: Questionnaires were sent to physical therapists working at 223 adult day care facilities in Chiba Prefecture, Japan. The number of all chronic stroke patients attending the day care who could walk without human assistance, including those who used a walking aid and/or an orthosis; the number of patients with genu recurvatum in the paretic limb during walking; and the number of patients with genu recurvatum who had experienced any knee pain in the last month were investigated. Physical therapists were also asked whether they considered genu recurvatum in stroke patients to be problematic. RESULTS: Sixty-four facilities (28.7%) responded, providing data on 1110 ambulatory stroke patients, of whom 217 (19.5%) showed genu recurvatum. Of the patients with genu recurvatum, 25 (11.5%) experienced knee pain in the paretic limb. Of 45 physical therapists who gave an opinion on whether genu recurvatum was problematic, 26 (57.8%) thought it was problematic whereas 19 thought it was not problematic. CONCLUSION: Rates of genu recurvatum and associated knee pain were relatively low among ambulatory community-dwelling stroke survivors attending adult day care.

Effects of Alternating Bilateral Training Between Non-Paretic and Paretic Upper Limbs in Patients with Hemiparetic Stroke: A Pilot Randomized Controlled Trial.

OBJECTIVE: To examine whether alternating training with both the non-paretic and paretic sides (alternating bilateral training), expecting trial-to-trial inter-limb transfer of training effects from the nonparetic to the paretic side, improves upper-limb motor performance in post-stroke patients, compared with unilateral training involving only the paretic side. DESIGN: An assessor-blinded pilot randomized controlled trial. SUBJECTS: Twenty-four right-handed post-stroke patients with hemiparesis. METHODS: Participants were randomly allocated to either an alternating bilateral training group or a unilateral training group (n = 12/group). Participants underwent dexterity training of the paretic arm using the Nine-Hole Peg Test, completing 10 trials/day for 7 consecutive days. The alternating bilateral training group additionally performed alternating trials with the non-paretic limb. Performance change, assessed 1 day and 1 week after the 7-day training period, was compared between groups. RESULTS: Although the improvement was comparable in both groups at both post-training time-points, a sub-analysis in which those with left hemiparesis and those with right hemiparesis were analyzed separately revealed potential benefits of the alternating bilateral training, specifically for those with left hemiparesis. CONCLUSION: Alternating bilateral training may augment training effects and improve upper-limb motor function in patients with left hemiparesis.

Efficiency and Stability of Step-To Gait in Slow Walking.

As humans, we constantly change our movement strategies to adapt to changes in physical functions and the external environment. We have to walk very slowly in situations with a high risk of falling, such as walking on slippery ice, carrying an overflowing cup of water, or muscle weakness owing to aging or motor deficit. However, previous studies have shown that a normal gait pattern at low speeds results in reduced efficiency and stability in comparison with those at a normal speed. Another possible strategy is to change the gait pattern from normal to step-to gait, in which the other foot is aligned with the first swing foot. However, the efficiency and stability of the step-to gait pattern at low speeds have not been investigated yet. Therefore, in this study, we compared the efficiency and stability of the normal and step-to gait patterns at intermediate, low, and very low speeds. Eleven healthy participants were asked to walk with a normal gait and step-to gait on a treadmill at five different speeds (i.e., 10, 20, 30, 40, and 60 m/min), ranging from very low to normal walking speed. The efficiency parameters (percent recovery and walk ratio) and stability parameters (center of mass lateral displacement) were analyzed from the motion capture data and then compared for the two gait patterns. The results suggested that step-to gait had a more efficient gait pattern at very low speeds of 10-30 m/min, with a larger percent recovery, and was more stable at 10-60 m/min in comparison with a normal gait. However, the efficiency of the normal gait was better than that of the step-to gait pattern at 60 m/min. Therefore, step-to gait is effective in improving gait efficiency and stability when faced with situations that force us to walk slowly or hinder quick walking because of muscle weakness owing to aging or motor deficit along with a high risk of falling.

Insensitivity of auditory mismatch negativity to classical fear conditioning and extinction in healthy humans.

The relationship between auditory mismatch negativity (MMN) and the neural cognitive processes of fear has been suggested in both healthy participants and patients with fear-related mental disorders such as post-traumatic stress disorder and panic disorder. The present study sought to confirm whether the MMN is affected by classical fear conditioning in healthy participants. MMN amplitude, N1 amplitude, and skin conductance level (SCL) in 20 healthy volunteers during a fear-conditioning paradigm consisting of three phases (habituation, fear acquisition, and fear extinction) were recorded. Red and blue light signals were presented as the conditioned stimuli CS+ (threat cue) and CS- (safety cue), respectively. In addition, an aversive electrical stimulus was delivered as the unconditioned stimulus with CS+ in the fear-acquisition phase. No MMN amplitude changes were observed between the CS types during the three phases. In the acquisition phase, the mean SCL during CS+ was significantly higher than that during CS-. The MMN amplitude and deviant N1 amplitude in the extinction phase were significantly lower than those in the other phases regardless of the CS type. Despite the clear alteration of SCL between CS types in the acquisition phase, no significant differences in MMN were observed. Decreased MMN and deviant N1 in the fear-extinction phase were considered to be mainly due to decreased arousal or attention level. Results indicate that the auditory MMN amplitude was not affected by the cognitive process of fear recognized by other sense modalities.

Transcranial direct current stimulation (tDCS) on the dorsolateral prefrontal cortex alters P50 gating.

Transcranial direct current stimulation (tDCS) has been reported to modify cortical function by inducing alterations in the underlying brain function. P50auditory evoked potentials, as assessed using a paired auditory stimulus (S1 and S2) paradigm, are thought to reflect a sensory gating process in which the functional involvement of the dorsolateral prefrontal cortex (DLPFC) is suggested. P50 sensory gating has also been reported to be associated with the pathogenesis of psychiatric diseases such as schizophrenia and anxiety-related disorders. Here we investigated whether the tDCS over the DLPFC could modulate the cortical function leading to alteration of the P50 sensory gating. P50 gating indices (the S2/S1 ratio and S1-S2 difference) were measured during the tDCS (current 1.0 mA, duration 15 min) over the DLPFC with different conditions (anodal, cathodal and sham). Ten male healthy volunteers were studied on separate days in a single blinded paradigm. We observed that the cathodaltDCS significantly altered the mean P50 gating indices compared to the other two conditions. Our results suggest that sensory gating could be modulated by cathodaltDCS on the left DLPFC but not by anodal/sham tDCS.

A comparison of the movement characteristics between the kneeling gait and the normal gait in healthy adults.

BACKGROUND: Trainings of the kneeling position, such as standing exercise on the knees and kneeling gait, have been anecdotally used in physical therapy to improve postural control of patients with various pathological conditions. However, clinical evidence is lacking and the movement characteristics of these kneeling trainings have not been well explored. The purpose of this study is to clarify the movement characteristics of the kneeling gait compared with the normal gait. METHODS: Twenty healthy volunteers (10 men and 10 women) aged 22-34 years were recruited. Participants were required to perform the kneeling gait and the normal gait at a self-selected comfortable speed on the treadmill. Surface electromyograms (EMG) and center of mass (COM) displacements were measured during each task. RESULTS: The EMGs of the gait-related proximal muscles during the kneeling gait were greater than during the normal gait, even at a comfortable speed. The COM displacement to the lateral direction was longer during the kneeling gait than it was during the normal gait. Furthermore, mechanical energy efficiency during the kneeling gait was less than that during the normal gait. CONCLUSION: The results suggest that the kneeling gait is an effective exercise to strengthen the gait-related proximal muscles. The increased muscle activities during the kneeling gait were probably due to the compensatory movements of the trunk and the pelvis.

P50 suppression in human discrimination fear conditioning paradigm using danger and safety signals.

Auditory P50 suppression, which is assessed using a paired auditory stimuli (S1 and S2) paradigm to record the P50 mid-latency evoked potential, is assumed to reflect sensory gating. Recently, P50 suppression deficits were observed in patients with anxiety disorders, including panic disorder, post-traumatic stress disorder and obsessive-compulsive disorder, as we previously reported. The processes of fear conditioning are thought to play a role in the pathophysiology of anxiety disorders. In addition, we found that the P50 sensory gating mechanism might be physiologically associated with fear conditioning and extinction in a simple human fear-conditioning paradigm that involved a light signal as a conditioned stimulus (CS+). Our objective was to investigate the different patterns of P50 suppression in a discrimination fear-conditioning paradigm with both a CS+ (danger signal) and a CS- (safety signal). Twenty healthy volunteers were recruited. We measured the auditory P50 suppression in the control (baseline) phase, in the fear-acquisition phase, and in the fear-extinction phase using a discrimination fear-conditioning paradigm. Two-way (CSs vs. phase) Analysis of variance with repeated measures demonstrated a significant interaction between the two factors. Post-hoc LSD analysis indicated that the P50 S2/S1 ratio in the CS+ acquisition phase was significantly higher than that in the CS- acquisition phase. These results suggest that the auditory P50 sensory gating might differ according to the cognition of the properties (potentially dangerous or safe) of the perceived signal.

Impaired P50 suppression in fear extinction in obsessive-compulsive disorder.

The processes of fear conditioning and extinction are thought to be related to the pathophysiology of anxiety disorders including obsessive-compulsive disorder (OCD). We have reported alterations of auditory P50 suppression in human fear conditioning and extinction in healthy control subjects (Kurayama et al., 2009). In the study, P50 suppression was impaired transiently in the course of fear acquisition and extinction. In this study, we investigated the changes of P50 suppression with OCD patients in the course of the same experimental paradigm. 39 patients with OCD and 21 healthy control subjects were recruited. In the acquisition phase of classical fear conditioning, 10 pairings of the conditioned stimulus (CS; the visual stimulus from a light-emitting diode) and the unconditioned stimulus (US; the electrical stimulus to the wrist) were administered, and in the extinction phase, 10 CS without US were administered. P50 auditory evoked potentials were measured as the first stimulus sound (S1) and the second stimulus sound (S2) in double-click paradigm with a 500 ms interval. P50 S2/S1 ratio was used to evaluate P50 suppression. The mean P50 S2/S1 ratio in patients with OCD significantly elevated from baseline level during the fear acquisition as that in healthy controls, but the elevated S2/S1 ratio did not recover to baseline level. The S2/S1 ratio in the extinction phase was significantly higher in the OCD patient group than in the healthy control group. In conclusion, our data suggested that P50 sensory gating in fear extinction was impaired in patients with OCD.

Alterations of auditory p50 suppression in human fear conditioning and extinction.

BACKGROUND: Auditory P50 suppression, assessed by using a paired auditory stimulus (S1 and S2) paradigm to record P50 mid-latency evoked potential, is assumed to reflect sensory gating. Recently, P50 suppression deficits were found in patients with anxiety disorders, including panic disorder, obsessive compulsive disorder, and posttraumatic stress disorder. The processes of fear conditioning are thought to play roles in pathophysiology of anxiety disorders. Our aim was to investigate whether sensory gating would be physiologically altered by fear conditioning. METHODS: To clarify the relationship between classical fear conditioning and the sensory gating mechanism, we measured changes of P50 and N100 suppression of 21 healthy volunteers in control (baseline) phase, in fear acquisition phase, and in fear extinction phase. RESULTS: The mean P50 S2/S1 ratio in fear acquisition phase was significantly elevated in comparison with that in control phase, and it recovered into basal level in extinction phase. In contrast, the mean N100 S2/S1 ratio showed no changes through all phases from fear acquisition to extinction. CONCLUSIONS: These results suggest that the P50 but not N100 sensory gating mechanism might be physiologically associated with fear acquisition and extinction.