Allelic variation in the serotonin transporter promoter modulates cortical excitability.

BACKGROUND

Transcranial magnetic stimulation (TMS) is a noninvasive procedure that may be used to study individual differences in motor cortex excitability. Such differences are assumed to reflect serotonergic and other inputs to the motor cortex.

METHODS

Here we investigate the impact of a functional polymorphism in the promoter region of the 5-hydroxytryptamine transporter gene (5-HTTLPR) on measures of motor cortex excitability.

RESULTS

Sixty healthy subjects carrying one or two copies of the short 5-HTTLPR allele (s/s and s/l) showed a significant reduction in short intracortical inhibition (SICI, p = .012) and an increased cortical silent period (p = .042) compared with 60 age- and sex-matched individuals homozygous for the long allele (l/l). In contrast, motor threshold and intracortical facilitation did not differ significantly between groups.

CONCLUSIONS

These results provide further evidence of a role for serotonergic transmission in the modulation of cortical excitability. Differential effects on the measures under study suggest a pattern of prioritization in bioamine regulation of cortical inhibition.