Altered regional activation of cortices related to “where” vision, including the motion and spatial visual perception, previously has been identified in Alzheimer’s disease (AD)/mild cognitive impairment (MCI) patients. More importantly, several studies have demonstrated^{1, 2} that the decline of “where” visual function may contribute to the intellectual deterioration in AD. Thus, better understanding of “where” visual dysfunction would be helpful for diagnosis of AD and interpretation of cognitive evaluations³. Therefore, in this study, in order to extend the knowledge on the impaired pattern of “where” visual perception in MCI patients, we aim to further investigate the connectivity of the “where” visual networks in terms of intrinsic interaction in early and late MCI patients.To achieve the above aim, the study was carried out in two steps. First step, the activation likelihood estimation (ALE) analysis, a coordinate-base meta-analysis approach, was performed to locate the cortices of “where” visions. The coordinates of “where” visual cortices were obtained from the results of ALE analysis, and then were applied in second step to define the cortical regions of interest (ROIs) of HLV cortices. In the second step, the resting-state functional MRI (rs-fMRI) data of 131 subjects (including 52 early MCI (EMCI), 35 late MCI (LMCI) and 44 normal control (CN)) from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database (adni.loni.usc.edu) were analyzed to investigate the alternations of “where” visual network. The resting-state functional connectivity (RSFC) between each pair of ROIs calculated as the correlation between the rs-fMRI time courses of the two ROIs was compared among the three groups.

Cortices and ROIs of “where” vision

Totally, 22 significant clusters were found, which were mainly located in the bilateral occipital complex, superior parietal lobule, postcentral gyrus, inferior frontal gyrus and fusiform gyrus (Figure1). Based on the coordinates and BA regions of these clusters, 25 spherical ROIs were defined for “where” visual networks.

Interregional RSFC changes

Significant altered connectivities among the three groups included right postcentral gyrus-right fusiform, left postcentral gyrus-right fusiform and right fusiform-right thalamus. The Post Hoc analysis demonstrated that all these altered connectivities were significantly increased in LMCI group (Figure2).

In the present study, based on the RSFC and the probabilistic mapping of “where” visual cortices, abnormal RSFC was identified among several connections of “where” visual network at the late MCI stage. The involved brain regions included the bilateral poscentral gyrus, fusiform gyrus and thalamus. The postcentral gyrus is consistently active during action perception and execution, and may thus be considered as a brain region for motion perception⁴. Besides, its increased activation in MCI was consistently found in Agosta F’s study⁵, thus may corroborate our findings. Finally, in line with previous studies⁶, increased correlation between thalamus and fusiform gyrus was found in AD patients, and correlated with cognitive decline. We speculated that the elevated RSFCs in late MCI patients may imply the disruption of “where” visual network in MCI patients.In this study, we investigated the “where” visual network changes in early and late MCI patients from the aspect of interregional connectivity. The findings indicated that the alternation of the “where” visual networks developed in late MCI stage, and confirmed our hypothesis. These findings could extend the current knowledge on the pattern of visual perceptual impairment in MCI patients, and could be helpful for understanding the neuroanatomical basis of their clinical dysfunctions.