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

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.

...Stimulant drugs such as amphetamine, methamphetamine, and/or cocaine have the greatest potential to affect learning of fine motor skills. These drugs cause acute accumulation of primarily dopamine in the synaptic cleft (for review [11, 12]) and their use has been shown to modulate plasticity in animals [13] and in the human motor cortex [14, 15]. For example, administration of a single therapeutic dose of amphetamine enhances use- (practice-) dependant plasticity in healthy adults [14, 15] and in some stroke patients [16]. Similar findings have also been observed following administration of a single dose of levodopa [17], a drug that promotes the synthesis of dopamine.

The relationship between amphetamine and use-dependent plasticity is likely to vary in a dose-dependent manner. In rodent prefrontal cortex, injection of a low-dose of amphetamine (0.1 mg/kg) results in acute enhancement of long-term potentiation whereas high doses (10 mg/kg) abolish long-term potentiation [13]. Furthermore, high doses of amphetamine or methamphetamine, like those used illicitly, are toxic to dopaminergic neurons (for review [11, 12]). Long-lasting changes in the human motor cortex and other movement-related brain regions have also been observed in individuals with a history of illicit stimulant use [18–20]. However, it is unclear if these long-lasting pathophysiological changes alter the ability of individuals to learn new fine motor skills. Preliminary evidence suggests that motor skill learning may be unaffected in the longer term given that individuals with a history of mixed illicit stimulant use can improve their performance on the grooved pegboard test across trials and adaptation of grip force during repeated lifting of a novel object has been observed in this population [21]. Furthermore, learning of a visuomotor tracking task (pursuit rotor) was not impaired in cocaine-dependent individuals undergoing detoxification during a 21-day inpatient substance abuse treatment program [22].

The aim of the current study was to further investigate the long-lasting effect of illicit stimulant use on learning of fine motor skills...

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