The Relationship between Executive Function and the Integrity of Cingulum Bundle in Patients with Mild Cognitive Impairment and Patients withMild Alzheimer’s Disease
Date Issued
2012
Date
2012
Author(s)
Lin, Yi-Cheng
Abstract
Backgroundand Purposes: Executive function is one of the most important predictors for conversion to Alzheimer’s disease (AD) from mild cognitive impairment (MCI). Cingulum bundle (CB) is one of the main associative fibers connecting the “executive control network” in the brain. However, it remains controversial regarding whether the degree of degeneration of the CB in patients with MCI and patients with AD, and concerning whether there is a correlation between the integrity of CB and the executive function of these patients. Therefore, the two purposes of this study were: (1) to compare the differences in the integrity of CB among patients with MCI, patients with mild AD, and age-matched healthy controls using diffusion spectrum imaging (DSI) of the brain and (2) to investigate the relationship between executive function and the integrity of CB in patients with MCI and patients with mild AD.
Methods: We originally recruited 34 subjects. Due to the poor quality of brain image data of one MCI subject and one healthy subject, we only analyzed data from the remaining 32 subjects, including 15 healthy controls (mean age= 71.1 ± 7.1 years), 8 MCI (mean age= 73.7 ± 8.2 years), and 9 mild AD (mean age= 74.7 ± 8.2 years), were analyzed. All subjects received the DSI MR scan of the brain and clinical neuropsychological tests. The latter included the Color Trails Test- Parts A and B (CTT-A and CTT-B, respectively) and the Nelson Modified Card Sorting Test (MCST) for assessing executive function; and the Mini-Mental State Examination (MMSE) for assessing overall cognitive function. In DSI data analysis, we used tract-specific analysis method and region of interest (ROI) analysis method to calculate the generalized fractional anisotropy (GFA) values of the entire CB and the anterior (aCB), middle (mCB), and posterior (pCB) segments of the CB of each hemisphere to serve as the quantitative measures of the CB integrity for each subject. The higher the GFA values are, the better the integrity of CB is.For statistical analyses, we compared group differences in GFA values and performance on executive function tests using the Kruskal-Wallis analysis of variance by ranks test. The Mann-Whitney U test was used for post-hoc analysis. The relationships between the performance on executive function tests and the GFA values were analyzed by using the Spearman''s rank correlation coefficients.
Results: Statistical results showed that patients with mild AD performed significantly poorer than the healthy control group on the number of completed set (p=0.008) and number of perseverative errors (p=0.003) of the MCST test, as well as on the CTT-A (p=0.001) and CTT-B (p=0.003). Performance on these executive function tests of the MCI group was better than that of the mild AD group and poorer than that of the healthy control group, but there were no significant group differences (p= 0.041~0.964)。Results of the tract-specific analysis method showed that the GFA values of the entire left CB (p=0.001) and left pCB(p=0.006) significantly smaller in the mild AD group compared to those of the healthy control group (p< 0.017). Results of the correlation analyses for the two patient groups showed that the time to complete the CTT-B was highly correlated with the GFA values of the entire left CB (rs= -0.628, p= 0.007), left pCB(rs= -0.613, p= 0.009), and right mCB(rs= -0.482, p= 0.05) calculated by using the tract-specific analysis method. This finding suggests that patients who performed poorer on CTT-B also had poorer structural integrity of their left entire CB, left pCB, and right mCB. In addition, patients’ number of non-perseverative errors on the MCST was significantly correlated with the GFA value of the right mCB (rs= -0.500, p= 0.04), suggesting that patients who presented a greater number of non-perseverative errors on the MCST also showed poorer integrity of the right mCB. Results of analyses using the GFA values obtained from the ROI method showed no significant group differences in any GFA value and no significant correlations between the GFA values and executive function performance (p=0.106~0.903)。
Conclusion.We concluded thatbased on the structural integrity measures derived from the tract-specific analysis method, patients with mild AD presented poorer structural integrity of the entire left CB and left pCB than the healthy controls. The executive function of patients with mild AD and patients with MCI was significantly correlated with the structural integrity of the entire left CB, left pCB, and right mCB. These findings suggest that the structural integrity of CB analyzed by using the tract-specific method could reveal CB fiber integrity degeneration that is associated with decline in executive function.
Subjects
alzheimer's disease
mild cognitive impairment
cingulum bundle
diffusion spectrum imaging
tract-specific analysis
Type
thesis
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