Freezing/festination during motor tasks in early-stage Parkinson's disease: A prospective study.

BACKGROUND: Parkinsonian patients have a tendency to speed up during repetitive motor tasks (festination) and to experience sudden motor blocks (freezing). In this article, we prospectively studied the appearance and progression of these phenomena in 30 early-stage PD patients. METHODS: A total of 30 controls and early-stage PD patients were assessed in the "off-drug" condition at baseline and 2 years later. Freezing of gait was evaluated using a standardized gait trajectory with the usual triggers. Patients also performed diadochokinetic tasks with 3 different effectors (repetitive, antiphase movements for the hands and feet, and repetitive syllable production for the orofacial effector) at frequencies ranging from 1 to 7 Hz (in random order). The primary endpoint was the occurrence of freezing and festination. RESULTS: At baseline, freezing was observed in 6.5% of the trials in PD patients (43% of the patients) and 2.3% of the trials in controls, and festination was observed in 5.7% of the trials in patients (53% of the patients) and 0.8% of the trials in controls. These proportions were slightly higher in patients 2 years later. None of the patients presented freezing of gait at baseline, but 2 displayed this condition 2 years later. These phenomena occurred more frequently for the limb effectors than for the orofacial effector. Freezing and festination were associated with the akinetic-rigid subtype, although tremor-dominant patients displayed greater rhythm variability outside episodes. CONCLUSION: Freezing and festination of the upper and lower limbs are observed soon after the diagnosis of PD and may be early biomarkers for disease progression. © 2016 International Parkinson and Movement Disorder Society.

Task-dependent changes in late inhibitory and disinhibitory actions within the primary motor cortex in humans.

The objective of the present study was to investigate the time course of long-interval intracortical inhibition (LICI) and late cortical disinhibition (LCD) as a function of the motor task (index abduction, thumb-index precision grip). Motor-evoked potentials were recorded from the first dorsal interosseus (FDI) muscle of the dominant limb in 13 healthy subjects. We used paired-pulse transcranial magnetic stimulation (TMS) paradigms in which a test pulse was preceded by a suprathreshold priming pulse (130% of the resting motor threshold) with varying interstimulus intervals (ISIs). In each task, double pulses were delivered with ISIs ranging from 30% of the corresponding silent period (SP; ~ 45 ms) to 220% of the SP (~ 330 ms). In both tasks, we found that LICI was followed by LCD (namely a period of increased cortical excitability lasting until ~ 200% of the SP). The time-dependent modulation of LICI and LCD differed in the two tasks; LICI was shorter (i.e. disinhibition occurred earlier) and LCD was more intense during precision grip than during index abduction. Long-interval intracortical inhibition disappeared well before the end of the SP in the precision grip task, suggesting that the mechanisms underlying these two inhibitory phenomena are distinct. Our data suggest that disinhibition might reflect adaptation of neural circuit excitability to the functional requirements of the motor task.

Influence of repetitive transcranial magnetic stimulation on tibialis anterior activity during walking in humans.

OBJECTIVE: To determine whether or not modulation of the excitability of the M1 region controlling the lower limb (using repetitive transcranial magnetic stimulation; TMS) would change the TA's activity during gait and the effect of aging on this change. METHODS: In three separate sessions, participants underwent different repetitive TMS (rTMS) protocols (sham stimulation, intermittent theta-burst stimulation (TBS) and continuous TBS) delivered over the M1 region controlling the lower limb muscles, using a focal, figure-of-eight coil. Before and after rTMS, the TA's activity was recorded using surface electrodes while participants walked at a freely chosen speed and at an imposed speed on a treadmill. Cortical excitability was assessed by characterizing input-output (IO) curves, after fitting the relationship between motor evoked potential amplitude and stimulus intensity with a Boltzmann sigmoidal equation. RESULTS: We did not observe any effects of rTMS in terms of TA activation during locomotion, gait parameters or IO curves in either healthy young adults or elderly adults. Elderly patients presented lower excitability of cortical TA representation area. CONCLUSION: Modulation of TA activity by TBS was ineffective contrary to what is observed for upper limbs. Interindividual variability in the effects of rTMS on TA activation, activation of the TA before the rTMS and/or differences in the depth of the cortical representation of the TA could have influenced the results and should be taken into account for further studies.

Self-perceived and actual ability in the functional reach test in patients with Parkinson's disease.

Falls frequently occur during daily activities such as reaching for an object in patients with Parkinson's disease (PD). Misjudgment is also reported to be one of the circumstances that lead to falls. The functional reach test is an indicator of dynamic balance. The primary objective was to establish whether there is a difference between self-perceived and actual ability to perform the functional reach test in patients with PD who have never fallen. Three groups of participants (all with no history of falls) were studied: young adults, elderly adults and PD patients. The participants first estimated their maximum reaching distance (but without performing the action, i.e. as a motor imagery task) and then actually performed the functional reach test (i.e. as a motor task). No significant overestimation or underestimation was observed. The reaching distance was lower in PD than in the two other groups. There were no differences between PD patients and elderly adults in terms of the forward centre of pressure displacement. Seven PD patients reported a fall in the year following the experiment. The fallers had a longer history of disease. Finally, PD patients adequately estimated their ability in the functional reach test and did not adopt an "at risk" strategy and appeared to be quite conservative (as were healthy elderly adults) in their postural control behavior. Ability to estimate self-performance is preserved in PD patients with no clinical impairments of postural control although they are at risk of future falls.