Abnormalities of inhibitory neuronal mechanisms in the motor cortex of patients with schizophrenia.
BACKGROUND
Focal transcranial magnetic stimulation (TMS) of the motor cortex was used to study two cortically activated inhibitory neuronal mechanisms that suppress ongoing tonic voluntary electromyographic activity in contralateral (postexcitatory inhibition [PI]) and ipsilateral (transcallosal inhibition [TI]) hand muscles. The PI follows the corticospinally mediated excitatory motor response (MEP) and is influenced by dopaminergic neurotransmission. TI reflects transcallosally mediated inhibition of the contralateral motor cortex, leading to motor inhibition in muscles ipsilateral to stimulation. PI and TI were studied to explore whether dopaminergic neurotransmission or interhemispheric transfers are altered in schizophrenia.


METHODS
TMS was performed in 16 patients with this disease and in 16 healthy control subjects. Surface electromyographic activity was recorded bilaterally from the first dorsal interosseous muscle during a sustained strong isometric contraction.


RESULTS
When compared with the findings in healthy subjects, patients with schizophrenia had a significantly longer PI and TI. The changes of the PI support the notion of an overactivity of the central dopaminergic system in schizophrenia.


CONCLUSIONS
The prolonged TI suggests an abnormal activation of interhemispheric connections between the motor cortices and may be related to previously reported pathology of the corpus callosum in schizophrenic patients.
Bajbouj
M
M
Labor für Klinische Psychophysiologie, Department of Psychiatry, Freie Universität Berlin, Berlin, Germany. malek.bajbouj@medizin.fu-berlin.de
Gallinat
J
J
Niehaus
L
L
Lang
U E
UE
Roricht
S
S
Meyer
B-U
BU
D000293:Adolescent; D000328:Adult; D014150:Antipsychotic Agents / Q000627:therapeutic use; D016022:Case-Control Studies; D002746:Chlorpromazine / Q000627:therapeutic use; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology / Q000528:radiation effects; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology* / Q000528:radiation effects; D009433:Neural Inhibition / Q000528:radiation effects; D012559:Schizophrenia / Q000503:physiopathology* / Q000628:therapy; D018709:Statistics, Nonparametric
D014150:Antipsychotic Agents; D002746:Chlorpromazine