Investigating the Utility of Markers of Cortical Excitability in Schizophrenia

Schizophrenia is an illness characterized by distributed dysfunction in numerous cortical and subcortical regions. Transcranial Magnetic Stimulation (TMS) is a promising research tool for directly examining the excitability of neural networks, a measure that has been termed cortical excitability. Cortical excitability has been found to be related to meaningful symptom correlates in schizophrenia, such as executive functioning. Despite evidence for widespread pathology across cortical regions, cortical excitability via direct stimulation of the cortex has infrequently been examined outside of prefrontal regions. The present study: 1) investigated cortical excitability using a combined Transcranial Magnetic Stimulation (TMS) and electroencephalography (EEG) paradigm in speech production regions (“Broca’s area” BA 45, F7 electrode) in schizophrenia, and 2) examined the relationship between cortical excitability and verbal learning and memory (Hopkins Verbal Learning Task; HVLT). Contrary to our hypotheses, cortical excitability did not differ between individuals with schizophrenia/schizoaffective disorder and the comparison group without neurologic or psychiatric illness. Furthermore, no relationship was found between cortical excitability and verbal learning or memory in either group or in a combined group of all participants. Verbal learning and memory performance did not differ between groups. Findings may be the product of our relatively high performing sample, heterogeneous illness duration, insufficient power, and/or the fact that only gamma frequency band was examined, suggesting the need for additional study. It is also possible that the absence of differences in cortical excitability in speech production regions suggests a localized deficit in prefrontal regions, rather than a global deficit