Impairment of the visuospatial working memory in the patients with Parkinson's Disease: an fMRI study
Shoji Kawashima1, Yoko Shimizu2, Yoshino Ueki2
1Department of Neurology and Neuroscience, Graduate School of Medical Science, Nagoya City University, 1 Kawasumi, Mizuho-ku, 467-8601, Nagoya, Japan. shojiyuto@wf6.so-net.ne.jp.
Background:
Mild cognitive impairment (MCI) is a common symptom in the patients with Parkinson's disease (PD). The characteristics of cognitive impairment in PD are executive function (including working memory) and visuo-perceptual processing. The visuospatial n-back test has the merit of minimizing the influence of educational biases involved in the verbal n-back test. Furthermore, it can assess both visuospatial recognition and working memory in a single test.
Methods:
We aimed to clarify the advantage of the visuospatial n-back test as a tool for detecting impairments of working memory in PD. We enrolled 28 right-handed patients with PD (18 males, 10 females) and 12 age-matched healthy controls (HC; 7 males, 5 females). Thirteen patients were classified as MCI (PD-MCI), and 15 as cognitively normal PD (PD-CN). Using functional MRI (fMRI), we explored the specific brain regions associated with the performance of the n-back test in the PD-MCI, PD-CN, and HC groups. The 0-back test assesses visuospatial recognition, while the 1-back and 2-back tests assess visuospatial working memory. Group comparisons were performed for three loads of this test.
Results:
Patients with PD performed significantly worse in terms of the correct answer rates of all n-back tests compared with HC. fMRI analyses performed during the 2-back test revealed reduced activation in the bilateral dorsolateral prefrontal cortex, middle frontal gyrus (MFG), and parietal lobule in the PD group compared with the HC group. In contrast, the fMRI result during the 0-back test showed only a marginal difference in the frontal lobe. On comparisons of task performance between the PD-MCI and PD-CN groups, we found that the correct answer rate in the 2-back test was lower in the PD-MCI group than in the PD-CN group. However, scores of the 0-back and 1-back tests were not significantly different between the two groups. The fMRI findings revealed that activations within the middle frontal gyrus (MFG) and inferior parietal lobule (IPL) during the 2-back test were reduced in the patients with PD-MCI when compared to those with PD-CN.
Conclusions:
This study reports reduced activation of the MFG and IPL in patients with PD-MCI. These regions may be associated with the pathophysiology of working memory impairment in patients with PD, which involves fronto-striatal network dysfunction.
Insights
Parkinson's disease patients show impaired working memory, particularly those with mild cognitive impairment (MCI). Functional MRI revealed reduced brain activation in key areas during memory tasks, suggesting fronto-striatal network dysfunction in PD-MCI.
Area of Science:
- Neuroscience
- Cognitive Neurology
- Medical Imaging
Background:
- Mild cognitive impairment (MCI) is prevalent in Parkinson's disease (PD), affecting executive functions like working memory.
- Visuospatial n-back tests offer an advantage over verbal tests by minimizing educational bias and assessing both recognition and working memory.
Purpose of the Study:
- To evaluate the efficacy of the visuospatial n-back test in identifying working memory deficits in Parkinson's disease patients.
- To investigate brain activation patterns using fMRI during visuospatial n-back tests in PD patients with and without MCI.
Main Methods:
- Functional MRI (fMRI) was employed to examine brain activity in 28 PD patients (13 PD-MCI, 15 PD-CN) and 12 healthy controls (HC) during 0-back, 1-back, and 2-back visuospatial tasks.
- The 0-back task assessed visuospatial recognition, while 1-back and 2-back tasks assessed visuospatial working memory.
- Group comparisons focused on brain activation differences in the prefrontal and parietal lobes.
Main Results:
- PD patients exhibited significantly lower correct answer rates across all n-back tests compared to HC.
- fMRI during the 2-back test showed reduced activation in the bilateral dorsolateral prefrontal cortex, middle frontal gyrus (MFG), and parietal lobule in PD patients versus HC.
- PD-MCI patients demonstrated lower correct answer rates on the 2-back test and reduced MFG and inferior parietal lobule (IPL) activation compared to PD-CN patients.
Conclusions:
- Reduced activation in the MFG and IPL during visuospatial working memory tasks is associated with PD-MCI.
- These findings suggest that fronto-striatal network dysfunction contributes to working memory impairments in Parkinson's disease.
