Motor cortex excitability correlates with an anxiety-related personality trait.
BACKGROUND
In an earlier study comparing obsessive-compulsive disorder (OCD) patients to psychiatrically screened normals, we found lowered motor evoked potential (MEP) threshold to transcranial magnetic stimulation (TMS) and decreased intracortical inhibition in OCD. We sought to determine whether this pattern was specific to OCD.


METHODS
We measured the threshold and amplitude of MEPs to single and paired (subthreshold-suprathreshold; 3, 4, 10, 15 msec intervals) TMS in 46 healthy volunteers (23 women, 23 men) who were given the NEO-PI-R personality inventory. Nineteen of the men also received cognitive and motor tests.


RESULTS
The paired-pulse conditioned/unconditioned MEP amplitude ratios correlated with Neuroticism (N), a stable measure of trait-level anxiety and other negative emotions, in the whole sample (r = 0.48; p = 0.0006), and in the men (r = 0.63; p = 0.0009). There were no other significant correlations.


CONCLUSIONS
This relationship reflects a factor that contributes to both personality and cortical regulation. It was not statistically significant in women, probably because of confounding hormonal influences on excitability. Decreased intracortical inhibition may be related more to trait anxiety and depression, which are high in OCD, than to OCD itself. However, the MEP threshold (significantly lowered in OCD) was unrelated to N.
Wassermann
E M
EM
Brain Stimulation Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 10, Room 5N226, Bethesda, MD 20892, USA.
Greenberg
B D
BD
Nguyen
M B
MB
Murphy
D L
DL
D000293:Adolescent; D000328:Adult; D000368:Aged; D001008:Anxiety Disorders / Q000175:diagnosis / Q000503:physiopathology*; D001143:Arousal / Q000502:physiology; D004574:Electromagnetic Fields; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D009771:Obsessive-Compulsive Disorder / Q000175:diagnosis / Q000503:physiopathology; D010555:Personality Inventory; D012684:Sensory Thresholds / Q000502:physiology