Twenty-seven PD patients without dementia (mean age: 69.5 years; SD: 6.1 years; 7 men and 20 women) who were hospitalized in Sendai-Nishitaga National Hospital participated in this study. The inclusion criteria for patients in this study were as follows: age between 50 and 80 years, age at onset above 40 years, Hoehn-Yahr stage from 1 to 4, and a score of 24 or higher on the Mini-Mental State Examination (MMSE) [
16]. The exclusion criteria were as follows: a medical history of disease of the central nervous system not directly related to PD (e.g., stroke, head injury, epilepsy), a history of deep brain stimulation surgery, a history of familial PD, concurrent psychiatric illness, such as schizophrenia or manic depression, a documented or suspected history of drug abuse and/or alcoholism, diabetes mellitus, and major abnormalities on brain MRI scans, such as cerebral infarction or tumor. No patient had self-control problems associated with dopamine dysregulation syndrome, such as addiction to gambling. The motor symptoms of the PD patients were evaluated using Hoehn-Yahr staging [
17] and the Unified Parkinson’s Disease Rating Scale (UPDRS) part III [
18]. Scores for the UPDRS part III were recorded while the patients were on medication. Twenty-nine HCs (mean age: 69.9 years; SD: 3.8 years; 10 men and 19 women) were recruited from a job placement center for elderly people with payment. The HCs had no medical history of psychiatric or neurological disease. Data from 27 HCs (mean age: 70.0 years; SD: 3.9 years; 10 men and 17 women) were used in subsequent data analyses because one participant refused to participate in the experimental task, which included emotionally negative pictures, and another participant was extremely disgusted by a snake shown in the experimental task. The optimal sample size (i.e., 27 for each group) was determined based on a G*Power analysis [
19] using a power of 0.95, a medium effect size of
f = 0.25 for analysis of variance (ANOVA) to test within-between interactions, and an
α level of 0.05; data collection ceased when this number was satisfied for the analysis. The demographic data of the PD patients and HCs are summarized in Table
1. No significant differences were observed between the PD patients and HCs with respect to age (
t(44.3) = − 0.32,
p = 0.75,
r = 0.05), years of education (
t(52) = 0.06,
p = 0.95,
r = 0.01), or sex (
χ2 = 0.77,
p = 0.38,
V = 0.12). The protocol was approved by the ethics committees of Sendai-Nishitaga National Hospital and Chuo University. All subjects gave written informed consent in accordance with the Declaration of Helsinki.
Age (mean ± SD) | 69.5 ± 6.1 | 70.0 ± 3.9 | † n.s. |
Sex (male:female) | 7:20 | 10:17 | ‡ n.s. |
Years of education (mean ± SD) | 13.8 ± 2.5 | 13.8 ± 1.9 | † n.s. |
Years of PD (mean ± SD) | 9.1 ± 6.3 | - | |
Levodopa equivalent dose (mg/day) (mean ± SD) | 661.1 ± 183.8 | - | |
UPDRS part III (mean ± SD) | 22.6 ± 13.9 | - | |
Hoehn-Yahr stage (mean ± SD) | 2.6 ± 0.6 | - | |
Stage I (n) | 0 | - | |
Stage II (n) | 13 | - | |
Stage III (n) | 13 | - | |
Stage IV (n) | 1 | - | |