History of Illicit Stimulant Use Is Not Associated with Long-Lasting Changes in Learning of Fine Motor Skills in Humans

Abstract

Little is known about the long-lasting effect of use of illicit stimulant drugs on learning of new motor skills. We hypothesised that abstinent individuals with a history of primarily methamphetamine and ecstasy use would exhibit normal learning of a visuomotor tracking task compared to controls. The study involved three groups: abstinent stimulant users (n = 21; 27 ± 6 yrs) and two gender-matched control groups comprising nondrug users (n = 16; 22 ± 4 yrs) and cannabis users (n = 16; 23 ± 5 yrs). Motor learning was assessed with a three-minute visuomotor tracking task. Subjects were instructed to follow a moving target on a computer screen with movement of the index finger. Metacarpophalangeal joint angle and first dorsal interosseous electromyographic activity were recorded. Pattern matching was assessed by cross-correlation of the joint angle and target traces. Distance from the target (tracking error) was also calculated. Motor learning was evident in the visuomotor task. Pattern matching improved over time (cross-correlation coefficient) and tracking error decreased. However, task performance did not differ between the groups. The results suggest that learning of a new fine visuomotor skill is unchanged in individuals with a history of illicit stimulant use.

Figure 1

Experimental apparatus for the visuomotor tracking task. (a) Subjects were instructed to match their index finger metacarpophalangeal (MCP) joint angle with a moving target displayed on a computer screen. The target moved across the screen while making unpredictable upward and downward movements. Abduction of the finger moved the feedback line downward while adduction moved the feedback line upward. The maximum MCP joint angle movement was ±10° from neutral. (b) Medial-lateral movement of the index finger was recorded with a potentiometer. The axis of rotation of the potentiometer was positioned over the MCP joint. Muscle activity was also recorded from the first dorsal interosseous muscle using surface EMG.

Figure 2

Single-subject data for the three-minute visuomotor tracking task. Data are from an individual in the stimulant group. (a) and (b) Raw metacarpophalangeal joint angle trace (grey line) and target line (black line) at the beginning of the first (0–30 s) and last (150–180 s) epoch, respectively. (c) and (d) Raw EMG traces for the accompanying time frame. (e) and (f) Cross-correlogram for the same subject for the first (0–30 s) and last (150–180 s) epoch, respectively.

Figure 3

Group data showing performance during the visuomotor tracking task. (a) Tracking error. (b) Maximum cross-correlation coefficient (derived from cross-correlation of the target angle with metacarpophalangeal joint angle). Data for the control (circles), stimulant (triangles), and cannabis (squares) groups are shown.

Figure 4

Correlation between duration of abstinence from stimulants and change in the tracking error across the visuomotor task. Single subject data for the stimulant group are shown and log duration of abstinence is plotted on the x-axis. The correlation did not reach statistical significance (r = 0.383, P = 0.085). Solid line shows the result of a linear regression analysis (P = 0.070).

Figure 5

Group data showing performance during the grooved pegboard test. Data for the control (circles), stimulant (triangles), and cannabis (squares) groups are shown.