Abstract
Parkinson’s disease (PD) is a neurodegenerative disease that is characterized by loss of dopaminergic neurons in the substantia nigra. Mild Cognitive impairment (MCI) and dementia may come along with the disease. New indicators are necessary for detecting patients that are likely to develop dementia. Electroencephalogram (EEG) Delta responses are one of the essential electrophysiological indicators that could show the cognitive decline. Many research in literature showed an increase of delta responses with the increased cognitive load. Furthermore, delta responses were decreased in MCI and Alzheimer disease in comparison to healthy controls during cognitive paradigms. There was no previous study that analyzed the delta responses in PD patients with cognitive deficits. The present study aims to fulfill this important gap. 32 patients with Parkinson’s disease (12 of them were without any cognitive deficits, 10 of them were PD with MCI, and 10 of them were PD with dementia) and 16 healthy subjects were included in the study. Auditory simple stimuli and Auditory Oddball Paradigms were applied. The maximum amplitudes of each subject’s delta response (0.5–3.5 Hz) in 0–600 ms were measured for each electrode and for each stimulation. There was a significant stimulation × group effect [F(df = 6,88) = 3,21; p < 0.015; = 0.180], which showed that the difference between groups was specific to the stimulation. Patients with Parkinson’s disease (including PD without cognitive deficit, PD with MCI, and PD with dementia) had reduced delta responses than healthy controls upon presentation of target stimulation (p < 0.05, for all comparisons). On the other hand, this was not the case for non-target and simple auditory stimulation. Furthermore, delta responses gradually decrease according to the cognitive impairment in patients with PD.Conclusion: The results of the present study showed that cognitive decline in PD could be represented with decreased event related delta responses during cognitive stimulations. Furthermore, the present study once more strengthens the hypothesis that decrease of delta oscillatory responses could be the candidate of a general electrophysiological indicator for cognitive impairment.
Highlights
Parkinson’s disease (PD) is a neurodegenerative disease that is characterized by loss of dopaminergic neurons in the substantia nigra
As it can be seen in the figure and the table the healthy controls had the highest delta responses upon target stimulation in comparison to non-target and simple auditory stimulation
The difference between target stimulation vs. non-target and simple auditory stimulation is evident for healthy controls, but these differences are less apparent in PD patients with dementia
Summary
Parkinson’s disease (PD) is a neurodegenerative disease that is characterized by loss of dopaminergic neurons in the substantia nigra. Primary symptoms of the disease include motor symptoms like tremor, rigidity, postural instability, bradykinesia. Motor symptoms show a good response to levodopa. Disorders of cognitive functions, such as impairments in executive functioning, working memory and attention may be present in PD (Soliveri et al, 2000; Lewis et al, 2003; Pollux, 2004). Mild cognitive impairment (MCI) in PD was first described by Caviness et al (2007a) as an intermediate condition between normal cognition and dementia (Aarsland et al, 2011). Studies show that the clinical picture that starts as MCI progresses to dementia in 60% of the patients (Hughes et al, 2000; Levy et al, 2000; Aarsland et al, 2003; Buter et al, 2008). Recent evidence suggests there may be subtypes of PD that may affect neurotransmitter systems other than dopamine, manifesting with different cognitive/behavioral courses (Kehagia et al, 2010; Bohnen and Albin, 2011; Moustafa and Poletti, 2013)
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