Abstract
Deficits in GABAergic inhibitory neurotransmission are a reliable finding in schizophrenia (SCZ) patients. Previous studies have reported that unaffected first-degree relatives of patients with SCZ demonstrate neurophysiological abnormalities that are intermediate between probands and healthy controls. In this study, first-degree relatives of patients with SCZ and their related probands were investigated to assess frontal cortical inhibition. Long-interval cortical inhibition (LICI) was measured from the dorsolateral prefrontal cortex (DLPFC) using combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG). The study presents an extended sample of 129 subjects (66 subjects have been previously reported): 19 patients with SCZ or schizoaffective disorder, 30 unaffected first-degree relatives of these SCZ patients, 13 obsessive-compulsive disorder (OCD) patients, 18 unaffected first-degree relatives of these OCD patients and 49 healthy subjects. In the DLPFC, cortical inhibition was significantly decreased in patients with SCZ compared to healthy subjects. First-degree relatives of patients with SCZ showed significantly more cortical inhibition than their SCZ probands. No differences were demonstrated between first-degree relatives of SCZ patients and healthy subjects. Taken together, these findings show that more studies are needed to establish an objective biological marker for potential diagnostic usage in severe psychiatric disorders.
Highlights
SCZ is a severe psychotic disorder characterized by positive symptoms, negative symptoms and cognitive impairments[1]
Farzan et al have demonstrated using TMS-EEG that long-interval cortical inhibition (LICI) of gamma oscillations were selectively impaired in the dorsolateral prefrontal cortex (DLPFC) of patients with SCZ compared to both healthy subjects and treated patients with bipolar disorder[22]
These findings suggest that LICI abnormalities may be specific to SCZ and are not part of a generalized deficit associated with severe psychopathology
Summary
SCZ is a severe psychotic disorder characterized by positive symptoms, negative symptoms and cognitive impairments[1]. Saka et al.[21], evaluated TMS measures of inhibition in unaffected first-degree relatives of SCZ patients compared to healthy subjects (no proband group was assessed). It was found that frontal LICI was significantly reduced in SCZ patients, compared to OCD patients and healthy subjects, showing no effect of antipsychotic medication[23]. These findings suggest that LICI abnormalities may be specific to SCZ and are not part of a generalized deficit associated with severe psychopathology. TMS evoked potentials are thought to reflect changes in cortical excitability potentially related to longer lasting underlying inhibitory post-synaptic potentials and excitatory post-synaptic potentials rather than neural firing
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