Spatiotemporal Gait Patterns During Overt and Covert Evaluation in Patients With Parkinson´s Disease and Healthy Subjects: Is There a Hawthorne Effect?

Parkinson's disease (PD) and aging lead to gait impairments. Some of the disturbances of gait are focused on step length, cadence, and temporal variability of gait cycle. Under experimental conditions gait can be overtly evaluated, but patients with PD are prone to expectancy effects; thus it seems relevant to determine if such evaluation truly reflects the spontaneous gait pattern in such patients, and also in healthy subjects. Thirty subjects (15 subjects with PD and 15 healthy control subjects) were asked to walk using their natural, preferred gait pattern. In half of the trials subjects were made aware that they were being evaluated (overt evaluation), while in the rest of the trials the evaluation was performed covertly (covert evaluation). During covert evaluation the gait pattern was modified in all groups. Gait speed was significantly increased (P = .022); step cadence and average step length were also significantly modified, the average step length increased (P = .002) and the cadence was reduced (P ≤ .001). Stride cycle time variability was unchanged significantly (P = .084). These changes were not significantly different compared between elderly and young healthy controls either. Due to the small sample size, a note of caution is in order; however, the significant results suggest that covert evaluation of gait might be considered to complement experimental evaluations of gait.

The effects of expectancy on corticospinal excitability: passively preparing to observe a movement.

The corticospinal tract excitability is modulated when preparing movements. Earlier to movement execution, the excitability of the spinal cord increases waiting for supraspinal commands to release the movement. Movement execution and movement observation share processes within the motor system, although movement observation research has focused on processes later to movement onset. We used single and paired pulse transcranial magnetic stimulation on M1 (n = 12), and electrical cervicomedullary stimulation (n = 7), to understand the modulation of the corticospinal system during the "preparation" to observe a third person's movement. Subjects passively observed a hand that would remain still or make an index finger extension. The observer's corticospinal excitability rose when "expecting to see a movement" vs. when "expecting to see a still hand." The modulation took origin at a spinal level and not at the corticocortical networks explored. We conclude that expectancy of seeing movements increases the excitability of the spinal cord.

Effects of early or late-evening fatiguing physical activity on sleep quality in non-professional sportsmen.

BACKGROUND: This study aims to understand whether night sleep-quality is distorted by fatiguing physical activity (PA) when conducted early or late in the evening. METHODS: Nine males (18-38yrs) performed sessions of fatiguing-PA over 3 consecutive days (Mon-Wed), for 2 weeks. One week the PA was performed at 17h, and in the other week at 21h. A Control-week included no PA (PAABSENT). The fatiguing-PA sessions comprised several sets of the 20m Shuttle-Run-Test (20mSRT). Sleep was assessed by actigraphic recordings acquired over three nights each week. It included the nights following the PA-sessions and the same days in the week of PAABSENT. Sleep-quality perception was evaluated by mean of the National Sleep Foundation-Sleep Diary. The heart-rate (HR) and body-temperature (BT) at bed-time and waking-up were also registered. RESULTS: Neither the 20mSTR-estimated VO2max nor the number of maximal 20mSRT sets were different in the PA17h and PA21h sessions. Compared to the PAABSENT, the PA17h and PA21h sessions increased the HR at bedtime, which recovered to baseline level after the night of sleep. BT was also reduced when waking-up compared to bed-time, but this was also observed in PAABSENT. Sleep parameters measured by means of actigraphy were not modified by fatiguing activity when compared to PAABSENT. Nevertheless, the subjective perception of sleep-quality was negatively altered by fatiguing PA. CONCLUSIONS: Fatiguing PA performed early or late at the evening has no impact on objective sleep-quality but, subjectively, a deterioration of sleep-quality is perceived by the subjects.

Bilateral tDCS on Primary Motor Cortex: Effects on Fast Arm Reaching Tasks.

BACKGROUND: The effects produced by transcranial direct current stimulation (tDCS) applied to the motor system have been widely studied in the past, chiefly focused on primary motor cortex (M1) excitability. However, the effects on functional tasks are less well documented. OBJECTIVE: This study aims to evaluate the effect of tDCS-M1 on goal-oriented actions (i.e., arm-reaching movements; ARM), in a reaction-time protocol. METHODS: 13 healthy subjects executed dominant ARM as fast as possible to one of two targets in front of them while surface EMG was recorded. Participants performed three different sessions. In each session they first executed ARM (Pre), then received tDCS, and finally executed Post, similar to Pre. Subjects received three different types of tDCS, one per session: In one session the anode was on right-M1 (AR), and the cathode on the left-M1 (CL), thus termed AR-CL; AL-CR reversed the montage; and Sham session was applied likewise. Real stimulation was 1mA-10min while subjects at rest. Three different variables and their coefficients of variation (CV) were analyzed: Premotor times (PMT), reaction-times (RT) and movement-times (MT). RESULTS: triceps-PMT were significantly increased at Post-Sham, suggesting fatigue. Results obtained with real tDCS were not different depending on the montage used, in both cases PMT were significantly reduced in all recorded muscles. RT and MT did not change for real or sham stimulation. RT-CV and PMT-CV were reduced after all stimulation protocols. CONCLUSION: tDCS reduces premotor time and fatigability during the execution of fast motor tasks. Possible underlying mechanisms are discussed.

Effects of movement imitation training in Parkinson's disease: A virtual reality pilot study.

BACKGROUND: Hypometria is a clinical motor sign in Parkinson's disease. Its origin likely emerges from basal ganglia dysfunction, leading to an impaired control of inhibitory intracortical motor circuits. Some neurorehabilitation approaches include movement imitation training; besides the effects of motor practice, there might be a benefit due to observation and imitation of un-altered movement patterns. In this sense, virtual reality facilitates the process by customizing motor-patterns to be observed and imitated. OBJECTIVE: To evaluate the effect of a motor-imitation therapy focused on hypometria in Parkinson's disease using virtual reality. METHODS: We carried out a randomized controlled pilot-study. Sixteen patients were randomly assigned in experimental and control groups. Groups underwent 4-weeks of training based on finger-tapping with the dominant hand, in which imitation was the differential factor (only the experimental group imitated). We evaluated self-paced movement features and cortico-spinal excitability (recruitment curves and silent periods in both hemispheres) before, immediately after, and two weeks after the training period. RESULTS: Movement amplitude increased significantly after the therapy in the experimental group for the trained and un-trained hands. Motor thresholds and silent periods evaluated with transcranial magnetic stimulation were differently modified by training in the two groups; although the changes in the input-output recruitment were similar. CONCLUSIONS: This pilot study suggests that movement imitation therapy enhances the effect of motor practice in patients with Parkinson's disease; imitation-training might be helpful for reducing hypometria in these patients. These results must be clarified in future larger trials.

Balancing the excitability of M1 circuitry during movement observation without overt replication.

Although observation of a movement increases the excitability of the motor system of the observer, it does not induce a motor replica. What is the mechanism for replica suppression? We performed a series of experiments, involving a total of 66 healthy humans, to explore the excitability of different M1 circuits and the spinal cord during observation of simple movements. Several strategies were used. In the first and second experimental blocks, we used several delay times from movement onset to evaluate the time-course modulation of the cortico-spinal excitability (CSE), and its potential dependency on the duration of the movement observed; in order to do this single pulse transcranial magnetic stimulation (TMS) over M1 was used. In subsequent experiments, at selected delay times from movement-onset, we probed the excitability of the cortico-spinal circuits using three different approaches: (i) electric cervicomedullary stimulation (CMS), to test spinal excitability, (ii) paired-pulse TMS over M1, to evaluate the cortical inhibitory-excitatory balance (short intracortical inhibition (SICI) and intracortical facilitation (ICF)], and (iii) continuous theta-burst stimulation (cTBS), to modulate the excitability of M1 cortical circuits. We observed a stereotyped response in the modulation of CSE. At 500 ms after movement-onset the ICF was increased; although the most clear-cut effect was a decrease of CSE. The compensatory mechanism was not explained by changes in SICI, but by M1-intracortical circuits targeted by cTBS. Meanwhile, the spinal cord maintained the elevated level of excitability induced when expecting to observe movements, potentially useful to facilitate any required response to the movement observed.