Structure And Functional Connectivity Of The Hippocampus In Alzheimer's Disease And Amnestic Mild Cognitive Impairment

Objective:Alzheimer's disease(AD)is the most common type of dementia during geriatrie stage with an irreversible progress.Early diagnosis and intervention may delay the aggravation.Amnestic mild cognitive impairment(aMCI)is presently considered as the prodromal stage of AD due to its high risk of conversion.Impairment of episodic memory,the characteristic symptom of AD and aMCI,is closely related to hippocampus.Thus,alterations of hippocampal structure,structural connectivity and functional connectivity can explore the mechanisms.Multi-modality magnetic resonance imaging(MRI)technology has been widely used in AD and aMCI.Structural MRI(sMRI)offer meticulous depiction for brain structure,functional MRI(fMRI)mirror the synchronism of neuronal activity by functional connectivity(FC),and diffusion tensor imaging(DTI)evaluate the integrity of white matter fibres.Therefore,the present study aimed the hippocampal alterations of structure,structural connectivity and functional connectivity in AD and aMCI by multi-modality MRI.Methods:Two cohort data were contained.A dataset of sMRI was previously collected by our team,including 38 AD,33 aMCI patients and 45 normal controls(NC).The subregional morphology were explored based on radiomics features of anterior and posterior hippocampus.Another sample of multi-modality MRI included 42 AD,37 aMCI and 43 NC subjects.Firstly,based on fMRI dataset,brain regions which had changed FC with anterior and posterior parts of hippocampus were overlapped,then FC between these overlapped regions and hippocampal subregions were further compared in three groups.Secondly,hippocampus and its main projective region,thalamus,were further selected as region of interest(ROI),and deterministic fiber tracking was used for analyisi of DTI dataset.The alterations of connective fibres integrity and FC strength between hippocampus and thalamus were explored in AD and aMCI,as well as the correlation of these alterations.Results:(1)Morphological changes of hippocampal subregions based on radiomic features in AD and aMCI.Radiomic features in anterior and posterior parts of billateral hippocampus had significant differences in AD,aMCI and NC,correlated with degree of cognitive impairment,as well as classified AD from NC.These features provide more meticulous morphological changes for hippocampal subregions,thus can be a potential biomarker for early diagnosis of AD.(2)FC alteration pattern of hippocampal subregions in whole brain level.FC between left hippocampal subfields and overlapped regions all decreased in AD when compared to aMCI and NC.However,FC between right ones showed various alteration patterms.Most of the above FC correlated with degree of cognitive impairment.This indicated that FC alteration pattern were distinct in billateral hippocampus.(3)The alterations of structural connectivity and functional connectivity between hippocampus and thalamus in AD and aMCI.The integrity of billateral connective fibres were damaged when compared AD and NC but no differences were observed in FC.When correlated the connective fibres intigrity with FC strength between hippocampus and thalamus,a positive correlation were found in the left but no correlation in the right.This indicated that structural connectivity between left hippocampus and thalamus can influnce FC in AD and aMCI.Conclusion:Hippocampal alterations of structure,structural connectivity and functional connectivity in AD and aMCI,correlate with cognitive impairment and can be potential biaomarker for early idendification.Multi-modality MRI provide important conditions to further understand these alterations pattern.