Sarah Vercruysse

Freezing of gait in Parkinson's disease: The impact of dual‐tasking and turning

Background: Turning is the most important trigger for freezing of gait (FOG) in Parkinsons disease (PD), and dual‐tasking has been suggested to influence FOG as well. Objective: To understand the effects of dual tasking and turning on FOG. Methods: 14 Freezers and 14 non‐freezers matched for disease severity and 14 age‐matched controls were asked to turn 180° and 360° with and without a cognitive dual‐task during the off‐period of the medication cycle. Total number of steps, duration, cadence, freezing‐frequency, and secondary‐task performance were measured. Results: Seven freezers froze during the protocol. Freezing occurred in 37.5% of trials during 180° turning compared to 0% during straight‐line walking (X2 = 10.44, p < 0.01). The occurrence of FOG increased during 360° when also a dual‐task was added (X2 = 4.23, p = 0.04). Freezers took significantly more steps and were slower than controls in all conditions. The presence of a dual‐task increased these differences. Cadence increased significantly for freezers during 360° and 180° compared to straight‐line walking. In contrast, cadence was decreased during turning in controls and non‐freezers. During straight‐line walking, only freezers made errors in the secondary task. Controls increased their error‐rate during 180° turning, whereas freezers deteriorated their secondary task performance during 360°. Conclusions: 360° turning in combination with a dual‐task is the most important trigger for freezing. During turning, non‐freezers and controls decreased their cadence whereas freezers increased it, which may be related to FOG. Freezers adopted a posture second strategy in contrast to non‐freezers when confronted with a dual task.

Upper limb movement interruptions are correlated to freezing of gait in Parkinson’s disease

Freezing of gait (FOG) in patients with Parkinson’s disease (PD) is a common problem of unknown origin, which possibly reflects a general motor control deficit. We investigated the relationship between the frequency of freezing episodes during gait and during a bimanual task in control and subjects with PD with and without FOG. Group differences in spatiotemporal characteristics were also examined as well as the effects of visual cueing. Twenty patients with PD in the off‐phase of the medication cycle and five age‐matched controls performed a repetitive drawing task in an anti‐phase pattern on a digitizer tablet. The task was offered at two different speeds (comfortable and maximal) and two different amplitudes (small and large) with and without visual cueing. The results showed that freezing episodes in the upper limbs occurred in only 10.4% of patient trials and that their occurrence was correlated with FOG scores (Spearman’s rho = 0.64). Overall, few spatiotemporal differences were found between freezers, non‐freezers and controls, except for an overshooting of the target amplitude in controls. Effects of visual cueing were largely similar in all groups, except for the variability of relative phase, which decreased in non‐freezers and controls, and was unaffected in freezers. Despite the fact that general motor differences between subgroups were small, freezing episodes were manifest during a bimanual repetitive upper limb task and were correlated to FOG. Further study into upper limb movement breakdown is warranted to understand the parallel deficits that lead up to FOG.

Conflict and freezing of gait in Parkinson's disease: support for a response control deficit.

We investigated response activation and suppression processes in Parkinsons disease patients with freezing of gait (FOG). Fourteen freezers, 14 nonfreezers, and 14 matched healthy controls performed the attention network task (ANT) and the Stroop task. The former task has more stimulus-response overlap and is expected to elicit stronger irrelevant response activation, requiring more inhibition. Congruency effects were used as a general measure of conflict resolution. Supplementary reaction time (RT) distribution analyses were utilized to calculate conditional accuracy functions (CAFs) and delta plots to measure response activation and suppression processes. In agreement with previous research, freezers showed a general conflict resolution deficit compared with nonfreezers and healthy controls. Moreover, CAFs pointed to a strong initial incorrect response activation in FOG. As expected, conflict resolution impairment was only apparent in the ANT, and not in the Stroop task. These results suggest an imbalance between automatic and controlled processes in FOG, leading to a breakdown in both motor and cognitive response control.

Freezing of Gait in Parkinson Disease Is Associated With Impaired Conflict Resolution

Background. Freezing of gait (FOG) in Parkinson disease (PD) may involve executive dysfunction. This study examined whether executive functioning and attention are more affected in patients with FOG compared with those without and determined whether these processes are influenced by anti-Parkinson medication. Methods. A total of 11 PD patients with FOG, 11 without FOG, and 10 healthy control subjects, matched for age, gender, and education, participated. General motor, mental and cognitive screening tests, as well as specific neuropsychological assessment of executive functions and the Attention Network Test (ANT) were administered. The ANT was conducted in both ON and OFF phases in a counterbalanced design to determine medication-specific effects. Results. FOG showed a clear association with impairment in the executive control network for conflict resolution (inhibition of unwanted responses and impaired response selection), compared with nonfreezers and healthy controls, F(2, 28) = 5.41, P = .01. Orienting and alerting function did not differ between groups, F < 1. Other executive functions, such as abstract problem solving and mental flexibility were not associated with FOG (P > .10). Anti-Parkinson medication did not ameliorate conflict resolution (P > .10), although orienting attention improved with medication, F(1, 17) = 9.81, P < .01. Conclusions. This study shows an association between impaired conflict resolution and FOG, important in understanding the interplay between cognitive and motor problems, which can lead to specific rehabilitation strategies.

Freezing of gait in Parkinson's disease: disturbances in automaticity and control

Recent studies emphasize a key role of controlled operations, such as set-shifting and inhibition, in the occurrence of freezing of gait (FOG) in Parkinsons disease (PD). However, FOG can also be characterized as a de-automatization disorder, showing impairments in both the execution and acquisition of automaticity. The observed deficits in automaticity and executive functioning indicate that both processes are malfunctioning in freezers. Therefore, to explain FOG from a cognitive-based perspective, we present a model describing the pathways involved in automatic and controlled processes prior to a FOG episode. Crucially, we focus on disturbances in automaticity and control, regulated by the frontostriatal circuitry. In complex situations, non-freezing PD patients may compensate for deficits in automaticity by switching to increased cognitive control. However, as both automatic and controlled processes are more severely impaired in freezers, this hampers cognitive compensation in FOG, resulting in a potential breakdown. Future directions for cognitive rehabilitation are proposed, based on the cognitive model we put forward.

Freezing of Gait in Parkinson’s Disease: Where Are We Now?

Freezing of gait (FOG) is defined as a brief, episodic absence or marked reduction of forward progression of the feet despite the intention to walk. It is one of the most debilitating motor symptoms in patients with Parkinson’s disease (PD) as it may lead to falls and a loss of independence. The pathophysiology of FOG seems to differ from the cardinal features of PD and is still largely unknown. In the present paper, we review the studies that were performed since 2011 on methods to provoke and assess FOG and discuss new insights into behavioral and neural mechanisms underlying this clinical phenomenon. We conclude that most of the work reviewed confirms that gait pattern generation disturbances are central to FOG. The finding that FOG reflects a combined motor and cognitive de-automatization deficit, which may not be sufficiently offset by executive control, probably acts as parallel mechanism.

Cognitive aspects of freezing of gait in Parkinson’s disease: a challenge for rehabilitation

Freezing of gait (FOG) is a very disabling symptom affecting up to half of the patients with Parkinson’s disease (PD). Evidence is accumulating that FOG is caused by a complex interplay between motor, cognitive and affective factors, rather than being a pure motor phenomenon. In the current paper, we review the evidence on the specific role of cognitive factors in FOG. Results from behavioral studies show that patients with FOG experience impairments in executive functioning and response selection which predict that motor learning may be compromised. Brain imaging studies strengthen the neural basis of a potential association between FOG and cognitive impairment, but do not clarify whether it is a primary or secondary determinant of FOG. A FOG-related reduction of cognitive resources implies that adaptation of rehabilitation interventions is indicated for patients with FOG to promote the consolidation of learning.

Motor Imagery Ability in Patients With Early- and Mid-Stage Parkinson Disease

Background. Motor imagery has recently gained attention as a promising new rehabilitation method for patients with neurological disorders. Up to now, however, it has been unclear whether this practice method can also be successfully applied in the rehabilitation of patients with Parkinson disease (PD). Objective. This study aimed to investigate whether the motor imagery ability of patients with PD is still intact despite basal ganglia dysfunctioning. Methods. A total of 14 patients with early- and mid-stage PD (Hoehn and Yahr 1-3) and 14 healthy controls were evaluated by means of an extensive imagery ability assessment battery, consisting of 2 questionnaires, the Chaotic Motor Imagery Assessment battery, and a test based on mental chronometry. Results. PD patients performed the imagery tasks more slowly than controls, but the motor imagery vividness and accuracy of most patients were well preserved. Conclusions. These results are promising regarding the potential use of motor imagery practice in the rehabilitation of patients with PD.

Abnormalities and Cue Dependence of Rhythmical Upper-Limb Movements in Parkinson Patients With Freezing of Gait

Background. Freezing of gait (FOG) is a significant clinical problem in Parkinson disease (PD). Similar freezing-like episodes occur during finger movements, but little is known about ongoing motor problems during repetitive hand movements. Objective. To investigate if the regulation of bimanual movements is impaired in those with FOG and if withdrawal of an auditory cue amplifies this problem. Methods. A total of 23 PD patients (11 with and 12 without FOG) and 11 controls (CTRLs) performed repetitive finger movements, either externally paced or following cue withdrawal. Movement frequency, amplitude, and coordination pattern were manipulated. The stability and accuracy of movement were evaluated after exclusion of freezing trials. Results. With auditory pacing present, movement performance was comparable between groups. Following cue withdrawal, motor control deteriorated in those with FOG, resulting in smaller and less stable amplitudes, hastened and more variable frequency, and decreased coordination stability. Conversely, the performance of those without FOG remained mostly similar to that of CTRLs. Conclusions. Compared with those without FOG, those with FOG show greater continuous dyscontrol of bimanual movements, similar to the continuous timing and scaling difficulties during locomotion. Those with FOG also benefit from auditory cueing during upper-limb movements, but these are highly cue dependent. This implies that internal timekeeping functions are more disturbed in those with FOG, who may require rehabilitation strategies for repetitive upper-extremity tasks that include cueing and imagery.

Freezing in Parkinson's disease: a spatiotemporal motor disorder beyond gait.

Freezing of gait (FOG) is an incapacitating problem in Parkinsons disease that is difficult to manage therapeutically. We tested the hypothesis that impaired rhythm and amplitude control is a common mechanism of freezing which is also present during other rhythmic tasks. Therefore, we compared the occurrence and spatiotemporal profiles of freezing episodes during upper limb motion, lower limb motion, and FOG. Eleven freezers, 12 non‐freezers, and 11 controls performed a rhythmic bilateral finger movement task. The triggering effect of movement speed, amplitude, and coordination pattern was evaluated. Regression slopes and spectral analysis addressed the spatial and temporal kinematic changes inherent to freezing episodes. The FOG Questionnaire score significantly predicted severity of upper limb freezing, present in 9 freezers, and of foot freezing, present in 8 freezers. Similar to gait, small‐amplitude movements tended to trigger upper limb freezing, which was preceded by hastened movement and a strong amplitude breakdown. Upper limb freezing power spectra were broadband, including increased energy in the “freeze band” (3–8 Hz). Contrary to FOG, unilateral upper limb freezing was common and occurred mainly on the disease‐dominant side. The findings emphasize that a core motor problem underlies freezing which can affect various movement effectors. This deficit may originate on the disease‐dominant body side and interfere with amplitude and timing regulation during repetitive limb movements. These results may shift current thinking on the origins of freezing as being not exclusively a gait failure.