Discrepancies between patient and caregiver reports of daily living abilities in Parkinson's disease.

Freezing of gait (FOG) is a “brief episodic absence or marked reduction of forward progression of the feet despite the intention to walk”; a debilitating symptom of Parkinson's disease, with prevalence reported between ∼37% for early stage (≤5 years) and ∼64% for advanced stage (≥ 9 years) and as high as 80% in later stages. FOG is associated with increased prevalence of falls and reduced quality of life of People with Parkinson's (PwP). FOG can manifest across different so-called phenotypes, such as trembling in place, shuffling forward, and akinesia. While there currently is no broad consensus on the specific pathogenesis of FOG, common triggers have been identified, such as doorways/narrow spaces, turning and multi-tasking. One specific factor that is often implicated in exacerbating FOG frequency and duration is anxiety. It is suggested that increased anxiety (i.e., physiological arousal) overwhelms pre-existing defective limbic circuitry and noradrenergic pathways, leading to neural and cognitive inefficiencies that worsen freezing. Based on the Attention Control Theory (ACT), this paper aims to study the role of specific anxiety-related attentional characteristics in FOG, as this may ultimately help inform intervention development. ACT describes how anxiety may lead to preferential engagement of the ventral stream of information processing and associated stimulus-driven attentional system at the expense of a decreased influence of the goal-directed (dorsal) attentional system. According to these predictions, PwP with high arousal would allocate attentional resources to processing threat-related stimuli (e.g., worrisome thoughts related to freezing, or threatening task-irrelevant distractors, like doorways) rather than to goal-directed attentional processes (e.g., focusing on the intended step), resulting in more frequent and severe freezing. However, based on ACT, and its predecessor Processing Efficiency Theory, it is also predicted that such negative effects of anxiety could be offset if PwP manage to maintain their attentional focus toward the intended movement goal, through increased mental effort and/or inhibition of distraction by threat-related stimuli. These theories are well supported by empirical evidence in performance contexts, such as sport or surgery as well as functional gait, especially in older adults at risk of falling. However, relatively little is known about the role of these proposed anxiety-related attentional characteristics in the context of FOG. There is evidence that worrisome thoughts and rumination (i.e., self-preoccupation with concerns over failure and expectations of negative consequences) are triggered by stressful situations and are prevalent in individuals high in trait anxiety such as older adults fearful about falling. While such worries may be acted on to make adaptive changes to behavior (e.g., walking with an assistive device), processing such thoughts while walking will be cognitively demanding, and will bias an individual's attention toward potential threats to balance (or in PwP: toward potential triggers for FOG). This may distract attention away from the movement task at hand and thus exacerbate FOG. These assertions are particularly relevant in the context of Parkinson's where increased conscious monitoring of ongoing movements is required to compensate for loss of movement automaticity. The negative effects of anxiety-induced rumination and worry may therefore be minimized by investing more conscious attention into controlling and monitoring ongoing movement. Nonnekes and colleagues identified 59 unique strategies for improving mobility in PwP, “where an overarching working mechanism involved in all was allocation of attention to gait, the introduction of goal directedness, and the use of motor programs that are less automatized than those used for normal walking”. Further, cueing and movement strategy (e.g., weight-shifting) interventions for FOG are thought to be effective, at least in part, because they compensate for deficient automaticity by engaging cortical networks involved in goal-directed attention. However, conscious goal-directed strategies are effortful and cognitively demanding and will become more difficult to employ as anxiety and overall task demands increase. This may be especially true for PwP, who often already demonstrate both strong conscious control of movement, as well as deficits in executive functions, such as inhibition and shifting of attention. This will likely compromise their ability to block out worrisome thoughts and shift attention back toward the movement task at hand.