Statistical characteristics of finger-tapping data in Huntington's disease

Abstract

Measuring the rate of finger tapping is a technique commonly used as an indicator of impairment in degenerative neurological conditions, such as Huntington's disease. The information it provides can be greatly enhanced by analysing not simply the overall tapping rate, but also the statistical characteristics of the individual times between each successive response. Recent technological improvements in the recording equipment allow the responses to be analysed extremely quickly, and permit modification of the task in the interest of greater clinical specificity. Here we illustrate its use with some pilot data from a group of manifest HD patients and age-matched controls. Even in this small cohort, differences in the responses are apparent that appear to relate to the severity of the disease as measured by conventional behavioural tests.

Fig. 1

Left The portable device for recording hand tapping. The subject taps on the circular sensor areas. Right A typical reciprobit plot of hand-tapping interval data from one subject in this study tapping alternately on the two sides: responses for right and left movements are combined. The points represent a cumulative histogram of the latencies (intervals between taps), plotted on a probability scale as a function of reciprocal latency

Fig. 2

Examples of unusual latency distributions. a A subject showing marked bimodality in the alternation task, with one group of responses around 300 ms and another around 450 ms: responses in each direction are very similar. b A subject showing sporadic inattention in the pronation task: in both directions a small group of responses (top right) is markedly delayed relative to the main distribution. c Marked left/right difference; responses to the right are about 40 ms faster (alternation task). d A manifest HD patient with exceptionally slow responses, affecting all three types of movement, but most marked for the pronation/supination task

Fig. 3

Average values of μ (left) and σ (right) analysed by type of response and category of participant (C control, M manifest HD). Error bars show 1SE

Fig. 4

Scatter plot of σ versus μ for the two groups of participants performing single tapping; despite the very small numbers in this pilot study, the manifest HD patients (red) seem to form a distinct cluster from the controls (black)

Fig. 5

Relation between μ and σ in each of three types of test, and the total motor score, across all manifest HD subjects and controls (the latter are assigned a TMS score of zero)