Altered prefrontal activity and connectivity predict different cognitive deficits in schizophrenia

Area of Science:

• Neuroscience
• Psychiatry
• Cognitive Science

Background:

• Cognitive dysfunction, including episodic memory (EM) and executive function (EF) impairments, is a core feature of schizophrenia.
• Previous neuroimaging studies implicated the prefrontal cortex (PFC) in these cognitive deficits.
• The role of intrinsic PFC defects, independent of confounds like motivation, remains unclear.

Purpose of the Study:

• To investigate intrinsic defects in prefrontal cortex (PFC) activity and connectivity in schizophrenia patients.
• To correlate these intrinsic defects with performance on episodic memory (EM) and executive function (EF) tasks.

Main Methods:

• Transcranial magnetic stimulation (TMS) combined with high-density electroencephalography (hd-EEG) was used to measure cortical activity and connectivity.
• Recordings were performed in parietal, motor, premotor, and PFC regions in 20 healthy individuals and 20 schizophrenia patients.
• Source modeling of TMS-evoked responses yielded measures of cortical activity (significant current density, SCD) and connectivity (significant current scattering, SCS).

Main Results:

• Schizophrenia patients exhibited reduced SCD and SCS in premotor and prefrontal areas compared to controls.
• These measures were most defective in the PFC.
• Reduced PFC SCD correlated negatively with performance on an EM task (CPWd), while higher SCS values were associated with more errors on an EF task (PCET).

Conclusions:

• Schizophrenia patients possess intrinsic defects in both PFC activity and connectivity.
• These intrinsic PFC deficits are specifically associated with impairments in cognitive abilities, including episodic memory and executive function.