- 學位論文
以功能性磁振造影探討年齡在海馬回縱軸於記憶登錄作業活動的影響
Age effects on hippocampal activation along the longitudinal axis in memory encoding task: An fMRI study
摘要
過去的結構性磁振造影研究發現海馬回在正常老化過程中，其縱軸後段較前段隨年齡呈現較明顯的萎縮，產生一縱軸的老化階程。過去較缺乏探討海馬回縱軸隨正常老化的功能性改變的研究。本研究以功能性磁振造影及感興趣區域(Region of Interest)探討年齡對海馬回縱軸在記憶登錄作業中的影響。本研究發現，海馬回後段在主要激發後段活動的對比中，隨年齡較前段呈現顯著的功能下降，但行為表現並未呈現顯著差異。在主要激發海馬回前段活動的對比中，年齡未對行為表現造成影響，功能上也未發現顯著差異。此結果與過去結構性與功能性磁振造影研究結果相符。在行為表現維持同樣水準的情形下，海馬回後段隨年齡呈現的功能下降，可能由其他腦區的功能上升來補償。海馬回後段隨年齡呈現的功能下降可能影響其縱軸的回路對聯結記憶的訊息處理。本研究結果顯示，在正常老化過程，海馬回之功能可能在行為表現未受影響之前就表現出功能的降低，且後段海馬回之功能所受的影響大於前段海馬回之功能。
並列摘要
Previous structural neuroimaging studies have found an anterior-posterior gradient of age-related volume reduction along the hippocampal longitudinal axis. However, there have been few functional neuroimaging studies that investigated this tendency in normal aging process. The current study applied functional MRI and ROI analysis to investigate the hippocampal activation during memory encoding tasks and the age-related changes along the hippocampal longitudinal axis in normal aging. 68 participants aged from 19 to 79 years old were recruited. The results showed a greater age-related functional reduction in the posterior hippocampus than the anterior hippocampus in the contrast that elicited posterior hippocampus primarily, while there was no significant effect of age on the behavioral performance. There was no significant age-related reduction in the contrast that elicited anterior hippocampus primarily, neither did age has a significant effect on the behavioral performance. This result was consistent with findings from previous structural neuroimaging studies. It was possible that the age-related functional reduction of the posterior hippocampus was compensated in other brain areas, while the behavioral performance was maintained at the same level. This anterior-posterior gradient of functional reduction might interfere with the memory association process, which was found to be possibly supported by the neural circuitry of the hippocampal longitudinal axis. This finding implicated an age-related functional reduction with the absence of decline in behavioral performance, and the normal aging process involved the posterior hippocampal functional reduction more than the anterior hippocampal functional reduction.