Converging evidence from electrophysiological studies suggests that in individuals with schizophrenia EEG fast frontal oscillations are reduced. It is still unclear whether this reduction reflects an intrinsic deficit of underlying cortical/thalamo-cortical circuits, and whether this deficit is specific for frontal regions. Recent electrophysiological studies in healthy individuals have established that, when perturbed, different brain regions oscillate at a specific, intrinsically generated dominant frequency, the natural frequency.
To assess the natural frequency of posterior parietal, motor, premotor, and prefrontal cortices, in schizophrenic and healthy controls.
High-density electroencephalogram (Hd-EEG) recordings during Transcranial Magnetic Stimulation (TMS) of four cortical areas were performed. Several TMS-evoked EEG oscillation parameters, including synchronization, amplitude, and natural frequency were compared across the schizophrenia and healthy control groups.
Wisconsin Psychiatric Institute & Clinic, University of Wisconsin-Madison
Twenty patients with schizophrenia and twenty age-matched healthy controls.
Main Outcome Measures
Hd-EEG measurements of TMS-evoked activity in four cortical areas, the positive and negative syndrome scale (PANSS), and performance scores (reaction time, accuracy) in two computerized tasks: the word memory (CPW) and the facial memory (CPF) tests.
Schizophrenia patients showed a slowing in the natural frequency of frontal/prefrontal regions compared to healthy controls (from an average of 2 Hz decrease for the motor area, to almost 10 Hz for the prefrontal cortex). The prefrontal natural frequency of individuals with schizophrenia was slower than in any healthy comparison subject, and correlated with both positive PANSS scores and reaction time in the CPW.
These findings suggest that patients with schizophrenia have an intrinsic slowing in the natural frequency of frontal cortical/thalamo-cortical circuits, that this slowing is not present in parietal areas, and that the prefrontal natural frequency can predict some of the symptoms as well as the cognitive dysfunctions of schizophrenia.