Study On The Distribution Of Hippocampal Lateralization By Using Navigation Task

Background: Memory refers to the psychological procedure of encoding,storing and retrieving to the environmental information,which is an essential and a core process of cognition.Hippocampus is an important part of human and other vertebrates' brains and plays a crucial role in spatial cognition and episodic memory.In clinical work,patients with epilepsy or brain tumors may need removing the unilateral or even bilateral hippocampus,which would have a serious impact on patient's memory function.The impact of unilateral hippocampus resection on patients' memory function depends on its lateralization.Excision of the dominant side of hippocampus would lead to more severe memory disorder.The study on the hippocampal lateralization through modern science and technology,carries out the research on the mechanism of hippocampus memory function.Meanwhile,it can predict the postoperative memory function changes and track memory remodeling after the surgery.Methods: This study recruited 20 healthy subjects and 1 clinical patient with left hippocampus lesions.None of them had historical mental illness and visual defect.Basing on the existing task state of f MRI,this experiment generated a special navigation task program of f MRI.After studying the task,the subjects completed the task during the MRI scanning.The behavior information was collected in studying phase while hippocampal MRI information were collected during MRI scanning.Hippocampal and parahippocampal lateralization indices(LI)were calculated based on memory-related brain activation,which indicated the lateralization of hippocampal and parahippocampal navigating function.Result: Hippocampus were activated in varying degrees in all subjects.In 75%(15/20)subjects parahippocampal gyrus were activated.The activation was mostly located at the posterior of the hippocampus.The lateralization of the hippocampus had no significant correlation with the lateralization of handedness in navigation task.44.4%(8/18)right-handed subjects were hippocampal right-side advantage.According to the group level analysis,the hippocampal LI was 0.763,and the parahippocampal gyrus LI was-0.056,which indicated that there was no explicit relevancy between the hippocampal and parahippocampal lateralization in navigation task.The neuroimaging result of clinical patient showed the unilateral activation of left hippocampus and parahippocampal gyrus,and both were posterior.Conclusion:(1)The f MRI spatial memory-navigation task designed and developed in this experiment can successfully activate the hippocampus of the subject,and the feasibility of its application to clinical patients is verified.(2)The experiment shows that the activation of the hippocampus and the parahippocampal gyrus is located at the posterior part.(3)The lateralization of the hippocampus in navigation task has no absolute relevancy with the distribution of the dominant hemisphere of the brain or the handedness.(4)The lateralization of the hippocampus and the parahippocampal gyrus has no definite relevancy in navigation task.