Impaired Dual-tasking Research Articles

Transcranial direct current stimulation of dorsolateral prefrontal cortex improves dual-task gait performance in patients with Parkinson’s disease: A double blind, sham-controlled study

BackgroundDespite advances in pharmacological treatments and surgical processes, the problem of impaired dual-tasking persists in people with Parkinson’s disease (PD). Recently, transcranial direct current stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) has shown the potential to improve dual-task walking. Research QuestionCan combining left DLPFC stimulation using tDCS with dual-task performance reduce the cost of dual-tasking in individuals with PD? MethodsWe conducted a sham-controlled, cross-over, and double-blind study to investigate the effect of combining tDCS with the dual-task walk and its sustained effects among people with PD. Twenty participants with PD completed two sessions (anodal or sham tDCS) with at least a 1-week gap. Stimulation involved transferring 2 mA current through the left DLPFC for 30 min. Single- and dual-task gait was assessed before, during, immediately after, 15, and 30 min after stimulation ceased. Phoneme verbal fluency task was given as the cognitive distractor during dual task. Results and ConclusionThe results of this study show that in the dual-task condition, participants walked faster at fifteen minutes (p = 0.017) and thirty minutes (p < 0.01) after anodal tDCS ceased compared to sham. Similarly, participants generated a higher number of words per minute at fifteen minutes (p = 0.017), and thirty minutes (p < 0.01) after anodal tDCS ceased compared to sham. Furthermore, the dual-task cost (DTC) associated with gait speed was significantly lower (p = 0.022) at fifteen minutes after anodal tDCS compared to sham tDCS. However, no significant effect of tDCS was observed on gait and cognitive performance under the single-task condition. In conclusion, left DLPFC stimulation can improve dual-tasking in participants with PD and the peaking of the tDCS effect was observed at fifteen minutes after stimulation ceased.

Impaired dual tasking in Parkinson's disease is associated with reduced focusing of cortico-striatal activity.

See Bell et al. (doi:10.1093/awx063) for a scientific commentary on this article. Impaired dual tasking, namely the inability to concurrently perform a cognitive and a motor task (e.g. 'stops walking while talking'), is a largely unexplained and frequent symptom of Parkinson's disease. Here we consider two circuit-level accounts of how striatal dopamine depletion might lead to impaired dual tasking in patients with Parkinson's disease. First, the loss of segregation between striatal territories induced by dopamine depletion may lead to dysfunctional overlaps between the motor and cognitive processes usually implemented in parallel cortico-striatal circuits. Second, the known dorso-posterior to ventro-anterior gradient of dopamine depletion in patients with Parkinson's disease may cause a funnelling of motor and cognitive processes into the relatively spared ventro-anterior putamen, causing a neural bottleneck. Using functional magnetic resonance imaging, we measured brain activity in 19 patients with Parkinson's disease and 26 control subjects during performance of a motor task (auditory-cued ankle movements), a cognitive task (implementing a switch-stay rule), and both tasks simultaneously (dual task). The distribution of task-related activity respected the known segregation between motor and cognitive territories of the putamen in both groups, with motor-related responses in the dorso-posterior putamen and task switch-related responses in the ventro-anterior putamen. During dual task performance, patients made more motor and cognitive errors than control subjects. They recruited a striatal territory (ventro-posterior putamen) not engaged during either the cognitive or the motor task, nor used by controls. Relatively higher ventro-posterior putamen activity in controls was associated with worse dual task performance. These observations suggest that dual task impairments in Parkinson's disease are related to reduced spatial focusing of striatal activity. This pattern of striatal activity may be explained by a loss of functional segregation between neighbouring striatal territories that occurs specifically in a dual task context.

High-level vestibular impairment in a veteran with mild traumatic brain injury

Background: Imbalance, dizziness and impaired dual tasking are common symptoms reported by veterans with mild traumatic brain injury (mTBI). According to a Congressional Research Service report in 2014, approximately 220 000 veterans have sustained TBI in Iraq and Afghanistan wars, with 82.4% diagnosed with mTBI. Symptoms of subtle balance impairment, resulting in decreased ability to dual-task are frequently overlooked during the initial evaluation. Therefore, clinicians need to detect these symptoms and establish a treatment plan to address the underlying causes. Currently, few studies have addressed imbalance as a result of subtle balance impairment in patients with mTBI, and none has examined veterans with mTBI. Aims: The aim of this study was to develop a systematic approach to the assessment and treatment of imbalance in a veteran with mTBI. The imbalance was a result of impairment in the constitutional components, i.e. somatosensory, vestibular and visual inputs to the brain. Methods: The patient was a 56-year-old veteran with mTBI and post-traumatic stress disorder, secondary to improvised explosive device blast exposure during the Iraq war in 2005. He was evaluated with clinical vestibular assessments, Dizziness Handicap Inventory, Activities-specific Balance Confidence Scale, functional gait and balance analyses, and posturography to determine sensory organisational deficits. The patient's past medical history did not show any comorbidity resulting in imbalance. The patient received one therapy session per week for 8 weeks to address his balance and sensory deficits. Data from outcome measures were analysed and compared with those collected at baseline. Results: The results indicated that the patient improved significantly on measures of balance and sensory integration deficits after the treatment protocol. Conclusions: Data from the sensory organisation test provided a reliable basis for the identification and treatment of balance deficits in a veteran with mTBI. An intervention, emphasising visual, vestibular and somatosensory integration, may result in significant improvement of the patient's functional balance.

Postural instability and fall risk in Parkinson’s disease: impaired dual tasking, pacing, and bilateral coordination of gait during the “ON” medication state

The interplay between gait and specific cognitive faculties, in particular executive function (EF) and dual tasking abilities, has been described in healthy adults and in patients with Parkinson's disease (PD). There is, however, little direct evidence on the relationship between cognitive function, gait, and fall risk in PD, especially in the "ON" state (i.e., under the influence of the anti-parkinsonian medications). To address this issue, we evaluated cognitive function and gait under usual walking and dual-task conditions in 30 patients with PD in the ON state of the medication cycle. Subjects were classified as fallers or non-fallers based on their history. A computerized battery quantified cognitive function. Gait was assessed under three conditions: (1) Usual walking, (2) While subtracting serial 3 s, and (3) While subtracting serial 7 s. The EF and attention scores were lower in the fallers, compared to non-fallers (P ≤ 0.037), but general measures of cognition, e.g., memory, (P = 0.341) were not. Gait speed, variability, and the bilateral coordination of gait were worse in the fallers in all conditions. The DT effects on gait variability and bilateral coordination were larger in the fallers (P = 0.044, P = 0.061, respectively). These results suggest that patients with PD who have a high risk of falling are more sensitive to DT effects, perhaps as a result of relatively poor EF. These cognitive and motor deficits may increase the likelihood of loss of balance during everyday attention-demanding tasks among patients with PD.