A Similar but Distinctive Pattern of Impaired Cortical Excitability in First-Episode Schizophrenia and ADHD

Background: First-episode schizophrenia (FE-SZ) and attention
deficithyperactivity disorder (ADHD) are both neuropsychiatric
disordersassociated with an impaired dopaminergic transmission.
Though displayingdifferent clinical phenotypes, a common
pathophysiological pathway isdiscussed controversially. Several
studies using transcranial magneticstimulation (TMS) revealed
abnormalities in human motor cortexexcitability in both
schizophrenia and ADHD patients. Studies oncortical excitability
comparing these two diseases directly are lacking.Method: In this
study, a total of 94 subjects were analyzed.Twenty-fiveFE-SZ
patients were directly compared with 28 ADHD patients and 41healthy
controls (HC). We investigated cortical excitability (inhibitoryand
facilitatory networks) with single- and paired-pulse TMS to the
leftand right motor cortex. Results: Compared to HC, FE-SZ/ADHD
patientsdisplayed an impaired cortical inhibition over the left
hemisphere.Apart from an enhanced intracortical facilitation, FE-SZ
patients didnot differ compared to ADHD patients in the main
outcome measures. Bothpatient groups presented a dysfunctional
hemispheric pattern of corticalinhibition and facilitation in
comparison with HC. Conclusion: Theresults of this study indicate a
pattern of cortical disinhibition andabnormal hemispheric balance
of intracortical excitability networks intwo different psychiatric
diseases. These effects might be associatedwith an imbalance in
GABAergic and dopaminergic transmission and mightprovide evidence
for a common pathophysiological pathway of bothdiseases.