Demonstration of Early Cognitive Impairment in Parkinson's Disease with Visual P300 Responses

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. Cognitive changes in PD are less observable than motor symptoms; thus, research on cognitive processes, which are known to be impaired from the early stages of PD, is minimal. The purpose of this study is to research the brain dynamics of cognitively normal PD patients and healthy elderly controls using event-related potentials (ERPs) and to evaluate their relationships with neuropsychological tests.

METHODS

Eighteen cognitively normal PD patients and 18 age-, gender-, and education-matched healthy controls were included in the study. Detailed neuropsychological tests were applied to all participants. Electroencephalography (EEG) was performed according to the international 10-20 system, and a classical visual oddball paradigm was used in the experiments. ERP responses in the 0.5 to 25 Hz frequency range were examined. P300 amplitude and latency values were measured from the F₃, F_z, F₄, C₃, C_z, C₄, P₃, P_z, P₄, O₁, O_z, and O₂ electrode sites. In addition, the correlations between P300 responses and neuropsychological test scores were analyzed.

RESULTS

Significant differences were found between the P300 amplitudes of cognitively normal PD patients and healthy elderly controls [F_(1,31)=9.265; p=0.005]. P300 amplitudes were significantly lower for PD patients at the F₃, F_Z, C_z, C₄, P_z, and P₄ electrode sites than for healthy elderly controls. Moderate correlations were found between Stroop test score and P₄ amplitude, digit span forward and C₃ and P_z amplitude, and digit span backward and O₁ amplitude.

CONCLUSION

The major finding of this study was the detection of cognitive changes by electrophysiological methods in PD patients who were indicated to be cognitively normal by neuropsychological tests. These finding suggests that cognitive changes in PD patients, which are not yet reflected in neuropsychological tests, may be detected by electrophysiological methods in earlier stages.

Can volumetric magnetic resonance imaging evaluations be helpful in the follow-up of cognitive functions in cognitively normal Parkinson's disease patients?

Background/aim

In this study, besides the evaluation of gray and white matter changes in cognitively normal Parkinson's disease (PD-CN) patients with volumetric magnetic resonance imaging (MRI) parameters, it was tried to show that some neuropsychological tests may be impaired in PD-CN patients.

Materials and methods

Twenty-six PD-CN patients and 26 healthy elderly (HC) participants were included in the current study. Global cognitive status was assessed using the mini-mental state examination (MMSE), and the Montreal cognitive assessment scale (MoCA). Attention and executive functions were evaluated using the Wechsler memory scale-revised (WMS-R) digit span test and trail making test (TMT) part A and part B, the Stroop test, semantic and phonemic fluency tests, and clock drawing test. Magnetic resonance imaging (MRI) was acquired according to the Alzheimer's disease neuroimaging initiative (ADNI) protocol.

Results

There were no significant differences among groups regarding age, sex, handedness, and years of education. In the comparison of the PD-CN group and the HC group, there was a statistical decrease in the total animal scores, lexical fluency, TMT part A and TMT part B scores in the PD-CN group. Subcortical gray matter volumes (GMV) were significantly lower in PD-CN patients. The PD-CN group had a significantly reduced total volume of right putamen and left angular gyrus compared to that in the HC group. We observed that putamen and angular gyrus volumes were lower in PD-CN patients. On the other hand, TMT part B may be a useful pretest in detecting the conversion of mild cognitive impairment in PD.

Conclusion

Significant MRI volumetric measurements and neuropsychological test batteries can be helpful in the clinical follow-up in PD-CN patients.