Motor-Independent Cognitive Testing in Motor Degenerative Diseases

Abstract

Cognitive function is tested through speech- or writing-based neuropsychological instruments. The application and validity of those tests is impeded for patients with diseases that affect speech and hand motor skills. We therefore developed a "motor-free" gaze-controlled version of the Trail Making Test (TMT), including a calibration task to assess gaze accuracy, for completion by means of an eye-tracking computer system (ETCS). This electronic TMT version (eTMT) was evaluated for two paradigmatic "motor-neurodegenerative" diseases, Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). We screened 146 subjects, of whom 44 were excluded, e.g., because of vision deficits. Patients were dichotomized into subgroups with less (ALS-, PD-) or severe motor affection (ALS+, PD+). All 66 patients and all 36 healthy controls (HC) completed the eTMT. Patients with sufficient hand motor control (ALS-, PD-, PD+) and all HC additionally completed the original paper-pencil-based version of the TMT. Sufficient and comparable gaze fixation accuracy across all groups and the correlations of the eTMT results with the TMT results supported the reliability and validity of the eTMT. PD+ patients made significantly more errors than HC in the eTMT-B. We hereby proved the good applicability of a motor-free cognitive test. Error rates could be a particularly sensitive marker of executive dysfunction.

Keywords: Parkinson’s disease; Trail Making Test; amyotrophic lateral sclerosis; cognition; executive functions; eye tracking; neuromuscular diseases; neuropsychological tests.

Figure 1

Flowchart of study enrollment for patients and healthy controls (HC).

Figure 2

Group comparisons and correlations for gaze accuracy and performance in TMT and eTMT. (a) Deviance (in degrees) between target and fixation in calibration task as measure of gaze accuracy; (b) correlation between written TMT-A and eTMT-A; (c) correlation between written TMT-B and eTMT-B; (d) completion times for eTMT subtests in comparison between groups; (e) B/A ratio of completion times for eTMT subtests in comparison between groups; (f) total number of errors in eTMT subtests in comparison between groups; (g) fixations per second in eTMT subtests in comparison between groups; (h) errors per fixation in eTMT subtests in comparison between groups. In figures (d–h): ° outliers: values below the first quartile or above the third quartile with a distance of 1.5 to 3 times the interquartile range; * extreme outliers: values below the first quartile or above the third quartile with a distance of more than 3 times the interquartile range.