C. Tard

Auditory cueing of gait initiation in Parkinson's disease patients with freezing of gait

OBJECTIVEnImpaired gait initiation (GI) in patients with advanced Parkinsons disease (PD) is a typical functional sign of akinesia. Failure to initiate the first step is frequently presented by patients with freezing of gait (FOG) and is often considered a sub-type of freezing. The literature on the effects of cueing of GI preparation and execution remains controversial. Our objective was to establish whether auditory cueing improves the preparation and/or execution of GI in PD patients with a history of FOG.nnnMETHODSnWe recorded first-step preparation and execution in 30 PD patients with confirmed FOG under two randomised conditions: self-triggered (ST) gait and gait cued by a sound beep in off- and on-dopa conditions. Anticipatory postural adjustments (APAs) were evaluated by monitoring the trajectory of the centre of pressure.nnnRESULTSnWe compared the patients with 30 patients without history of FOG and 30 healthy controls (HCs). l-Dopa only slightly improved the characteristics of APAs in freezers but was effective to improve gait hypokinesia. Auditory cueing was effective in improving step preparation in freezers, who showed adequate APAs more frequently. As seen with HCs and patients without FOG, patients released their APAs more quickly when auditory cueing was applied. However, cueing did not have a significant effect on step length. Clinically, auditory cueing also improved start hesitation in freezers.nnnCONCLUSIONSnAuditory cueing improved step preparation but not step execution in PD patients.nnnSIGNIFICANCEnA failure to link step preparation and execution during GI may explain the poor first-step execution seen in PD freezers.

Why we should study gait initiation in Parkinson's disease

The gait initiation process is of particular interest in Parkinsons disease because it combines motor and cognitive components of movement preparation (referred to as anticipatory postural adjustments) and movement execution (the step by itself). Moreover, gait initiation in Parkinsons disease is often affected by motor blocks (a subtype of the freezing of gait phenomenon). Gait initiation disturbances in Parkinsons disease include delayed release of anticipatory postural adjustments, hypokinetic anticipatory postural adjustments (reduced scaling) and bradykinetic anticipatory postural adjustments (abnormal timing). The most extreme form is freezing of gait with sometimes the absence of anticipatory postural adjustments. Other phenomena can be also described in some freezing patients (such as multiple anticipatory postural adjustments, described clinically as knee trembling). The fact that emotion, attention, external triggers and dopaminergic drugs can all modify this motor program suggests the existence of a complex pathophysiological mechanism that involves not only locomotor networks but also cortical areas and the basal ganglia system. Abnormal coupling between standing posture and anticipatory postural adjustments and between the latter and step execution appears to be a crucial part of the pathophysiological mechanism. Although external cueing appears to be of interest, few studies have provided evidence of the efficacy of various rehabilitation methods in routine care.

Attention modulates step initiation postural adjustments in Parkinson freezers

BACKGROUNDnIn view of freezing of gaits circumstances of occurrence in Parkinsons disease, attentional resources appear to be involved in step initiation failure. Anticipatory postural adjustments (APAs) are essential because they allow unloading of the stepping leg and so create the conditions required for progression. Our main objective was to establish whether or not a change in attentional load during step initiation modulates APAs differently in patients with vs. without freezing of gait.nnnMETHODSnThree groups of 15 subjects were recruited: elderly people and parkinsonian patients with or without freezing of gait. Attention was modulated before step execution by means of an auditory oddball discrimination task with event-related potential recording. The primary endpoint was the occurrence of inappropriate APAs following the attentional task, i.e. APAs not followed by a step after an intercurrent auditory stimulus.nnnRESULTSnIn parkinsonian patients with freezing of gait, inappropriate APAs were recorded in 63% of the trials and were observed more frequently than in patients without freezing of gait (51%) and elderly controls (48%). Furthermore, inappropriate APAs in freezers were longer and more ample than in parkinsonian non-freezers and controls. Lastly, postural preparation was impaired in the parkinsonian patients.nnnCONCLUSIONnOur results indicate that allocation of attentional resources during step preparation influences the release of APAs differently in freezers and non-freezers. Modulating attentional load is partly responsible for triggering an inappropriate motor program. This difficulty in focusing attention or resisting interference may contribute (at least in part) to the gait initiation failure observed in parkinsonian freezers.

The pattern of attentional deficits in Parkinson's disease

BACKGROUNDnCognitive impairment without dementia is frequent in Parkinsons disease. It often presents as a dysexecutive syndrome with deficient attentional resource allocation. The nature of attention deficits in Parkinsons disease has rarely been investigated with robust, theory-based tasks. The main objective of the present study was to investigate attention disorders in Parkinsons disease patients by applying a paradigm based on a model of attention. We also sought to identify the main demographic and clinical characteristics associated with attention deficits in Parkinsons disease.nnnMETHODSnEighty non-demented Parkinsons disease patients and 60 healthy controls participated in the study. Attention was assessed in a computer-controlled reaction time paradigm. The test session comprised a simple reaction time task and four choice reaction time tasks: a go/no-go task, a one-dimension, focused-attention task, a two-dimension, divided-attention task and an alternating task. Performance was assessed by composite measures: (i) cognitive reaction time, corresponding to the difference between the simple reaction time and the choice reaction time in the given condition, and (ii) reaction time variability, corresponding to the sum of the coefficients of variance of the reaction times. Accuracy was also considered.nnnRESULTSnApart from an overall slowing and greater reaction time variability, Parkinsons disease patients were only significantly impaired in the alternating condition. This set-shifting impairment was associated with their performance in the go/no-go and divided-attention conditions.nnnCONCLUSIONnOur systematic assessment of the different attentional subcomponents revealed that mental flexibility is particularly impaired in non-demented Parkinsons disease patients.

Brain metabolic abnormalities during gait with freezing in Parkinson's disease.

INTRODUCTIONnFreezing of gait (FoG) is a debilitating gait disorder in Parkinsons disease (PD). In advanced PD patients with FoG, the supraspinal locomotor network may be dysregulated (relative to similar patients without FoG) during gait. Here, we sought to characterize the metabolism of locomotor networks involved in FoG.nnnMETHODSnTwenty-two PD patients (11 with off-drug FoG and 11 without) each underwent two [(18)F]-fluorodeoxyglucose PET brain scans in the off-drug state: one at rest and another during radiotracer uptake while performing a standardized gait trajectory that incorporated the usual triggers for FoG.nnnRESULTSnFor the 11 freezers, FoG was present for 39% (± 23%) of the time during the gait trajectory. The FoG-associated abnormalities were characterized by (i) hypometabolism in frontal regions (the associative premotor, temporopolar and orbitofrontal areas, i.e. Brodmann areas 6 and 8), (ii) hypermetabolism in the paracentral lobule (Brodmann area 5), and (iii) deregulation of the basal ganglia output (the globus pallidus and the mesencephalic locomotor region).nnnCONCLUSIONnFoG during a real gait task was associated with impaired frontoparietal cortical activation, as characterized by abnormally low metabolic activity of the premotor area (involved in the indirect locomotor pathway) and abnormally high metabolic activity of the parietal area (reflecting the harmful effect of external cueing).

O172 Conflict resolution influences motor preparation of step initiation

Background Gait initiation is an automatized motor program. However, it can vary depending on attentional resources. Executive attention, an attentional process involved in cognitive control of action, could play a role in movement preparation. Objective to evaluate how executive control may modulate gait initiation. Methods The Attention Network Test was used to control the influence of executive attention on both gait initiation kinetic characteristics and associated brain cortical activity. Thirty healthy subjects performed this test, in standard (seated) and gait initiation tasks. Reaction times were measured for both tasks in each condition (conflict resolution or not); step execution time and anticipatory postural adjustments were also recorded for the initiation task. Cortical activity was recorded via a 128-channel electro-encephalogram. Event-related potential (P300 component) and event-related spectral perturbation between 4 and 30xa0Hz were analysed, after the target presentation, according to conflict resolution or not. Results As reaction time measured at upper limbs, step execution time was significantly longer during conflict resolution. This effect was concomitant with a larger proportion of anticipatory postural adjustments errors, leading to an increase in duration of postural preparation. Event-related potentials analyses revealed a modulation of parietal P300’s amplitude and latency (the amplitude was lower and the latency was longer in case of conflict resolution). Event-related spectral perturbation analyses showed a posterior alpha- and beta-band desynchronisation after the target presentation, both in standard and initiation conditions. Posterior alpha and beta oscillations were also modulated by executive control in both conditions. Significance Our results showed that the executive attentionalcomponent has an influence on gait initiation, by eliciting more errors in motor programming. These errors were associated with parietal cortical modulation involving posterior attentional networks during movement preparation.