Inhibition, executive function, and freezing of gait

Abstract

Background: Studies suggest that freezing of gait (FoG) in people with Parkinson's disease (PD) is associated with declines in executive function (EF). However, EF is multi-faceted, including three dissociable components: inhibiting prepotent responses, switching between task sets, and updating working memory.

Objective: This study investigated which aspect of EF is most strongly associated with FoG in PD.

Method: Three groups were studied: adults with PD (with and without FoG) and age-matched, healthy adults. All participants completed a battery of cognitive tasks previously shown to discriminate among the three EF components. Participants also completed a turning-in-place task that was scored for FoG by neurologists blind to subjects' self-reported FoG.

Results: Compared to both other groups, participants with FoG showed significant performance deficits in tasks associated with inhibitory control, even after accounting for differences in disease severity, but no significant deficits in task-switching or updating working memory. Surprisingly, the strongest effect was an intermittent tendency of participants with FoG to hesitate, and thus miss the response window, on go trials in the Go-Nogo task. The FoG group also made slower responses in the conflict condition of the Stroop task. Physician-rated FoG scores were correlated both with failures to respond on go trials and with failures to inhibit responses on nogo trials in the Go-Nogo task.

Conclusion: These results suggest that FoG is associated with a specific inability to appropriately engage and release inhibition, rather than with a general executive deficit.

Keywords: Parkinson's disease; conflict resolution; executive function; freezing of gait; inhibition.

Figure 1

Individual participant scores for the EF measures in which FR and NF were significantly different. Left plot: Average time to name a color in the Stroop conflict condition requiring inhibition of reading. Center plot: Average time to name a color in the Stroop conflict condition, corrected for both color naming time and reading time. Right plot: Percent of target misses in the Go-Nogo task (failure to respond to a Go stimulus within 1000 ms). Note: all of the points clustered around zero have an actual value of zero. One NF subject’s Stroop score was not recorded due to experimenter error.

Figure 2

Correlations between FoG ratings assigned by two physician observers and performance deficits in the Go-Nogo task, with best fitting linear regression lines. Left plot: percentage of false alarms (failure to withhold response to a Nogo stimulus). Right plot: percentage of target misses (failure to respond to a Go stimulus within 1000 ms). Note that all of the points clustered around zero have an actual value of zero. The solid regression lines were computed using all PD subjects, and the dashed lines were computed excluding subjects with a FoG rating of zero.