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Freezing of gait (FOG), an episodic gait disturbance characterized by the inability to generate effective stepping, occurs in more than half of Parkinson's disease patients. It is associated with both executive dysfunction and attention and becomes most evident during dual tasking (performing two tasks simultaneously). This study examined the effect of dual motor-cognitive virtual reality training on dual-task performance in FOG. Twenty community dwelling participants with Parkinson's disease (13 with FOG, 7 without FOG) participated in a pre-assessment, eight 20-minute intervention sessions, and a post-assessment. The intervention consisted of a virtual reality maze (DFKI, Germany) through which participants navigated by stepping-in-place on a balance board (Nintendo, Japan) under time pressure. This was combined with a cognitive task (Stroop test), which repeatedly divided participants' attention. The primary outcome measures were pre- and post-intervention differences in motor (stepping time, symmetry, rhythmicity) and cognitive (accuracy, reaction time) performance during single- and dual-tasks. Both assessments consisted of 1) a single cognitive task 2) a single motor task, and 3) a dual motor-cognitive task. Following the intervention, there was significant improvement in dual-task cognitive and motor parameters (stepping time and rhythmicity), dual-task effect for those with FOG and a noteworthy improvement in FOG episodes. These improvements were less significant for those without FOG. This is the first study to show benefit of a dual motor-cognitive approach on dual-task performance in FOG. Advances in such virtual reality interventions for home use could substantially improve the quality of life for patients who experience FOG.

Many genetic studies have demonstrated an association between the 7-repeat (7r) allele of a 48-base pair variable number of tandem repeats (VNTR) in exon 3 of the DRD4 gene and the phenotype of attention deficit hyperactivity disorder (ADHD). Previous studies have shown inconsistent associations between the 7r allele and neurocognitive performance in children with ADHD. We investigated the performance of 128 children with and without ADHD on the Fixed and Random versions of the Sustained Attention to Response Task (SART). We employed time-series analyses of reaction-time data to allow a fine-grained analysis of reaction time variability, a candidate endophenotype for ADHD. Children were grouped into either the 7r-present group (possessing at least one copy of the 7r allele) or the 7r-absent group. The ADHD group made significantly more commission errors and was significantly more variable in RT in terms of fast moment-to-moment variability than the control group, but no effect of genotype was found on these measures. Children with ADHD without the 7r allele made significantly more omission errors, were significantly more variable in the slow frequency domain and showed less sensitivity to the signal (d') than those children with ADHD the 7r and control children with or without the 7r. These results highlight the utility of time-series analyses of reaction time data for delineating the neuropsychological deficits associated with ADHD and the DRD4 VNTR. Absence of the 7-repeat allele in children with ADHD is associated with a neurocognitive profile of drifting sustained attention that gives rise to variable and inconsistent performance.

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