Functional brain imaging of speeded decision processing in Parkinson's disease and comparison with Schizophrenia

Abstract

This study examined whether Parkinson's disease (PD¹) and schizophrenia (SCZ²) share a hypo dopaminergic dysfunction of the prefrontal cortex leading to cognitive impairments in decision processing. 24 medicated PD patients and 28 matched controls performed the Eriksen flanker two-choice reaction time (RT³) task while brain activity was measured throughout, using functional Magnetic Resonance Imaging (fMRI⁴). Results were directly compared to those of 30 SCZ patients and 30 matched controls. Significant differences between SCZ and PD were found, through directly comparing the z-score deviations from healthy controls across all behavioral measures, where only SCZ patients showed deviances from controls. Similarly a direct comparison of z-score activation deviations from controls indicated significant differences in prefrontal and cingulate cortical activation between SCZ and PD, where only SCZ patients showed hypo-activation of these areas compared to controls. The hypo-activation of the dorsolateral prefrontal cortex was related to larger RT variability (ex-Gaussian tau) in SCZ but not PD patients. Overall, the concluding evidence does not support a shared neural substrate of cognitive dysfunction, since the deficit in speeded decision processing and the related cortical hypo-activation observed in SCZ were absent in PD.

Keywords: Dopamine hypo-frontality; Ex-Gaussian; Prefrontal cortex; Reaction time; Spatial attention; fMRI.