Elevated motor threshold in drug-free, cocaine-dependent patients assessed with transcranial magnetic stimulation

Background: Transcranial magnetic stimulation (TMS) provides a noninvasive method of examining cortical inhibitory and excitatory processes and cortical excitability in awake subjects. There is evidence from clinical and electroencephalographic (EEG) data that cortical excitability may be abnormal in some psychiatric populations. Chronic cocaine abuse influences a number of neurotransmitters that are involved in the excitatory/inhibitory balance of the cerebral cortex. This pilot study was conducted to ascertain the possible utility of TMS in examining cortical excitability in a population of chronic cocaine abusers. Methods: The right and left motor thresholds of ten cocaine-dependent subjects, according to DSM-IV, and ten normal control subjects were examined using single pulse TMS. Results: The resting motor thresholds resulting from stimulation of the right or the left motor cortical regions were significantly elevated in cocaine-dependent subjects compared with matched control subjects. Conclusions: These pilot data suggest that chronic cocaine use significantly alters cortical excitability in the direction of increased inhibition or decreased excitability. We hypothesize that this observation reflects adaptation to those effects of cocaine intoxication that promote cortical excitability and seizures.