Shared reduction of oscillatory natural frequencies in bipolar disorder, major depressive disorder and schizophrenia

- Frontal oscillatory natural frequencies were studied in major psychoses.
- All patients showed slower TMS/EEG gamma-band oscillations relative to controls.
- A common biological underpinning may be found in dysfunction of GABAergic circuits.

IntroductionRecent studies have demonstrated that cortical brain areas tend to oscillate at a specific natural frequency when directly perturbed by transcranial magnetic stimulation (TMS). Fast electroencephalographic (EEG) oscillations, which typically originate from frontal regions, have been reported to be markedly reduced in schizophrenia.MethodsHere we employed TMS/EEG to assess the natural frequency of the premotor area in a sample of 48 age-matched participants (12 each in major depression disorder (MDD)), bipolar disorder (BPD), schizophrenia (SCZ) and healthy controls. Event related spectral perturbations (ERSP) were obtained for each study participant using wavelet decomposition.ResultsTMS resulted in a significant activation of the beta/gamma band response (21-50 Hz) to frontal cortical perturbation in healthy control subjects. By contrast, the main frequencies of frontal EEG responses to TMS were significantly reduced in patients with BPD, MDD and SCZ (11-27 Hz) relative to healthy subjects.ConclusionsPatients with bipolar disorder, major depression and schizophrenia showed a significantly lower natural frequency of frontal cortico-thalamocortical circuits compared to healthy controls. These results suggest a common neurobiological mechanism of corticothalamic impairment. The most likely candidates include dysfunction of GABAergic circuits.LimitationsFurther studies are needed to consider other biological markers, gene variants, and their interaction with clinical variables.