Hypofunctioning of sensory gating mechanisms in patients with obsessive-compulsive disorder.
BACKGROUND
In obsessive-compulsive disorder (OCD) patients, functional abnormalities in basal ganglia/precentral circuitries cause cortical hyperexcitability and lack of inhibitory control. These loops can be partly explored by median-nerve somatosensory evoked potentials (SEPs), which functionally reflect the brain responsiveness to somatosensory stimuli. In healthy humans, SEPs' amplitude during voluntary finger movements is lower than during muscular relaxation (i.e., sensory gating). Cortical hyperexcitability in OCD could be eventually responsible for a reduction of sensory gating. This might have pathophysiologic implications for motor compulsions.


METHODS
Median-nerve SEPs were recorded in 11 OCD patients and 9 healthy volunteers during muscle relaxation ("Relax") or finger movements of the stimulated hand ("Move"). Latencies and amplitudes of pre- and postcentral SEP components were compared between groups during "Relax" and "Move" conditions.


RESULTS
In OCD patients, the responsiveness to sensory stimuli was enhanced for precentral SEPs. Sensory gating ("Relax" vs. "Move") in control subjects involved both pre- and postcentral SEPs, the former being reduced in amplitude by approximately 60%. In OCD patients, sensory gating was spatially restricted to precentral SEP components and was significantly reduced compared with control subjects (approximately 30%).


CONCLUSIONS
Enhanced precentral SEPs and hypofunctioning of centrifugal sensory gating in OCD might reflect the inability to modulate sensory information due to a "tonic" high level of cortical excitability of motor and related areas, likely resulting from basal ganglia dysfunction. This might offer new insights into the pathophysiology of OCD.
Rossi
Simone
S
Section of Neurology, Department of Neuroscience, Brain Stimulation and Evoked Potentials Lab, Policlinico Le Scotte, Viale Bracci, I-53100 University of Siena, Italy. Rossisimo@unisi.it
Bartalini
Sabina
S
Ulivelli
Monica
M
Mantovani
Antonio
A
Di Muro
Angela
A
Goracci
Arianna
A
Castrogiovanni
Paolo
P
Battistini
Noè
N
Passero
Stefano
S
D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004569:Electroencephalography / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D005385:Fingers / Q000503:physiopathology; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000528:radiation effects; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology*; D009771:Obsessive-Compulsive Disorder / Q000503:physiopathology*; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D013003:Somatosensory Cortex; D018709:Statistics, Nonparametric