老化擴大空間導航距離扭曲現象之神經機制

Abstract

人類估算空間距離時會使用兩種不同的參考框架：自我中心參考框架（egocentric reference frame），即物體相對於自身的空間編碼方式，此參考框架之神經編碼涉及枕葉（occipital）和頂葉（parietal）皮質；與地標中心參考框（allocentric reference frame），即空間的組成是由地標之間的位置進行編碼，其主要由神經編碼涉及枕葉和顳葉（temporal）皮質。然而，這些參考框架並非完全無誤，且在估算距離時仍會出現距離失真（distance distortion）的現象，更甚者，隨著年齡增長，其距離失真現象更加明顯。在過往研究中，關於年齡如何擴大距離失真之成因仍眾說紛紜，卻未有直接證據顯示距離失真與神經表徵之連結。有鑑於此，本研究假設距離失真與負責參考框架的神經表徵有關，包含自我中心和地標中心參考框架；若距離失真與自我中心參考框架有關，則在經歷距離失真時，與負責自我中心參考架構之腦區有神經關聯性（neural correlate）；反之，則與負責地標中心參考框架之腦區有神經關聯性。在本研究中，實驗參與者在進行功能性磁振造影（fMRI）掃描時，估算在虛擬空間中兩個地標之間的距離。除了傳統功能性磁振造影分析外，我們近一步分析與距離失真和腦區之間的神經相關性，以探討距離失真的成因。行為結果顯示，參與者在遠距離時低估，在近距離時高估。此外，年長參與者比年輕參與者出現更顯著的距離失真。神經方面，透過表徵相似性分析（RSA），我們發現年齡相關的神經機制差異與距離失真有關。年輕參與者在低估距離時呈現枕頂葉皮質的神經表徵，此表徵於過往研究中較為負責自我中心參考框架。相反地，年長參與者在低估時則使用枕顳葉皮質來處理地標中心參考框架。這種模式顯示，年齡相關的距離失真增強源於地標中心參考框架的變化，此發現與先前研究結果一致。

Humans estimate distances using two reference frames: egocentric, which encodes locations relative to oneself involved in the occipital and parietal cortices, and allocentric, which encodes locations between landmarks through the occipital and temporal cortex. However, these reference frames are not unerring, leading to distance distortion, further amplified by aging. The underlying rationales of age-related distortions in distance estimation remain unclear. We assumed that distance distortion is associated with the neural representations of spatial reference frames, such as egocentric and allocentric information. If the egocentric reference frame is involved, the corresponding brain regions are represented while experiencing distance distortion, as they are for the allocentric frame. In our paradigms, participants were required to estimate the distance among landmarks within a virtual environment during a spatial navigation paradigm while undergoing functional magnetic resonance imaging (fMRI). In the present study, we analyzed the neural correlates with distance distortion to investigate why distance distortion occurs. As a result, participants underestimated in the far distance and overestimated in the near distance. Also, older adults exhibited more significant distortion compared to younger adults. Additionally, representation similarity analysis (RSA) revealed that age-related distinctions in neural mechanisms correlate with distance distortion. Younger adults exhibited the occipital-parietal cortex while underestimating, with such neural patterns responsible for the egocentric reference frames. In contrast, older adults recruited the occipital-temporal cortex, which processes the allocentric spatial information, for underestimation. Such patterns indicate that the age-related amplified distance distortion may stem from altering the allocentric reference frame, aligning with findings from previous studies.