Dynamic Emotional Memory Network In Aging Brain

As people get older, many brain cognitive functions will suffer from age-related decline to some extend. However, compared with young people, there is reason to believe that the function of the emotional memory in older people tend to stay and show a positive affective bias. That is to say, older people tend to remember and recall more positive events than negative memories, or to be more responsive to the positive affairs than neutral and negative things. This age-related emotional memory changes become a hot topic in brain research. And it is of great significance in scientific research.To date, functional magnetic resonance imaging (FMRI) is one of the widespread non-invasive imaging techniques that used for investigating brain activity. By measuring changes in the local oxygenation of blood caused by neurons in brain, FMRI can detect the inner connections between different brain regions.The main work and innovative points of this study are list below:(1) As previous studies make great effort on task-based FMRI analysis, our research use resting-state FMRI data sets to investigate the age-related changes in emotional memory. This is a good complement for task-based FMRI researches.(2) Different from conventional temporal domain or frequency domain based functional connectivity methods, our research pioneering use of Wavelet Transform Coherence based time-frequency method to analyze the functional connectivity between brain regions which associate with emotional memory network.From our work, several important findings are found. And to our knowledge, those findings have not been seen reported by any other studies.(1) In emotional memory networks, the strength and pattern of functional connectivity between different brain regions is not constant during scan. On contrast, the functional connectivity reveals different strength and pattern as time and frequency changes.(2) Compared to young people, the decreased functional connectivity between amygdala and medial temporal lobe (hippocampus/ Parahippocampus cortex) are found in old people. But we do not find the increased functional connectivity between amygdala and prefrontal cortices. These findings can reflect that the spontaneous low-frequency BOLD fluctuations (LFBF) in resting state somehow reveal the positive affective bias of emotional memory during task-based condition.(3) The above-mentioned functional connectivity differences in emotional memory function not reveals in whole LFBF frequency band (i.e.0.01to0.1Hz), but mainly reflect in slow-4(0.01-0.027Hz) and slow-3(0.027-0.073Hz) of LFBF in resting state FMRI.The results verify the non-stationary characteristic of brain time series which extract from FMRI. At the same time, this study reveals the dynamic nature of emotional memory network and suggests that the age-related changes in emotional memory network may closely related to some special sub frequency bands of LFBF. Number of figures:32; Number of tables:3; Number of references:90.