Patients with early Alzheimer Disease (AD) and Mild Cognitive Impairment of the Amnestic type (MCI-A) have been reported to show large variability of tapping scores. Factors that contribute to that variability remain undetermined. This preliminary study aimed to identify predictors of finger tapping variability in older adults evaluated for a neurodegenerative memory disorder. Based on earlier research with normally functioning adults, we predicted that the number of “invalid” tapping responses (i.e. failure of the index finger to adequately lift off the tapping key once it is depressed to produce the next number on a mechanical counter) and the female gender would predict finger tapping variability, but age and educational level would not predict variability.

This preliminary study included 4 groups of participants, comprised of 8 healthy controls (HC, 3 males; 73±7years); 12 persons with subjective memory complaints (SMC, 3 males; 69±5 years); 12 with MCI-A (7 males; 76±5 years) and 7 early AD (5 males; 75±6years). All participants were administered a modified version of the Halstead Finger Tapping Test (HFTT). Mean, range of tapping score (i.e. a measure of variability), and number of invalid taps across 7 trials in each hand were calculated. ANOVA was performed for the HFTT metrics with the main effect of group. Tukey HSD tests were used for post hoc comparisons between groups. Multiple regression analysis was performed to determine the degree to which the number of invalid tapping responses, sex, age, and educational level predicted finger tapping variability using all 4 groups.

Mean tapping score did not vary significantly across groups in the dominant [F (3, 35) = 0.633, p = 0.599] or non-dominant [F (3, 35) = 2.345, p = 0.090] hand. Range score approached a significant difference between groups in the dominant hand [F (3, 35) = 2.745, p = 0.058], with a clear significant effect of group on range score in the non-dominant hand [F (3, 35) = 4.078, p = 0.014]. Range score in the nondominant hand was significantly higher in the AD compared to SMC (p = 0.018) and HC (p = 0.024). Regression analysis revealed statistically significant findings for the dominant hand (R2 = 0.327, F (4, 34) = 4.130, p = 0.008) and for the non-dominant hand (R2 = 0.330, F (4, 34) = 4.180, p = 0.007). For both the dominant and non-dominant hands, number of invalid taps significantly predicted range score (ß = 0.453, p = 0.044, and ß = 0.498, p = 0.012, respectively). Sex, age, and education years did not predict range scores.

Variability of finger tapping in patients evaluated for neurodegenerative memory disorders and aged matched controls is predicted by the number of invalid tapping responses (comprising over 30% of the variance), but not by demographic variables in this clinical sample. Neurodegenerative disorders may eliminate a sex effect.