ABERRANT FUNCTIONAL CONNECTIVITY OF THE THALAMUS IN A ONE-YEAR FOLLOW-UP STUDY OF MILD COGNITIVE IMPAIRMENT

Abstract

Most mild cognitive impairment (MCI) patients shared the same pathophysiology and similar symptoms with Alzheimer's disease (AD). Hence, it is great important to fully understand the clinical and pathophysiological changes in the MCI stage for the earlier diagnosis of AD. However, there were only few studies aiming at the longitudinal alteration of functional connectivity in MCI till now. The thalamus occupies the central position of human brain and was also considered to be central to the cortical functions. Moreover, the thalamus has been repeatedly found to be involved in some important resting-state networks, such as the default mode network, which is closely related to episodic memory. Increasing evidences have confirmed the significant volume loss and disrupted connectivity pattern of the thalamus in AD/MCI subjects. The present study is to investigate alteration of thalamic functional connectivity in patients with MCI during a one year follow-up. Neuropsychological tests and thalamic functional connectivity based on resting state functional magnetic resonance imaging (fMRI) were evaluated in 13 MCI subjects (age 74.5±8.7years, gender 8M/5F) both at the baseline and one year later. After mean 13 ± 2.2 months, one MCI subject converted to mild AD. The Montreal cognitive assessment (MoCA) score decreased significantly over the period (23.7±2.5 versus 21.7±4.7, p = 0.04), while the mini-mental state examination (MMSE) score decreased numerically in the follow-up (27.3±1.8 versus 25.8±3.4, p =0.10). Compared to the baseline, the MCI patients demonstrated decreased functional connectivity between the left thalamus and left inferior parietal cortex (IPC), left putamen and right cerebellar posterior lobe one year later. Decreased functional connectivity was also detected between the right thalamus and left putamen in the follow-up MCI. We suggest that the MoCA can be used as an effective tool in longitudinal studies of MCI. The impaired functional connection between the thalamus and various brain regions which are involved with higher cognition functions may be associated with the progression of illness in the MCI subjects. These results provided new evidence for the longitudinal alteration of the functional abnormality in the MCI. The brain regions exhibiting significant differences in functional connectivity of the bilateral thalamus in MCI patients. The color bar represents the strength of functional connectivity (p<0.01, cluster size >30 voxels). The individually longitudinal comparisons in the identified brain regions which showed altered functional connectivity in follow-up in the MCI patients. A represents the regions showed altered functional connectivity with the left thalamus. B represents the regions showed altered functional connectivity with the right thalamus. P value represents the significant between the baseline and the follow-up by using pair two-sample t-test.