導航能動性提升空間環境之神經表徵

Abstract

位於海馬迴中之網格細胞與位置細胞是為建立認知地圖之空間表徵。於本研究中，我們假設於導航期間，價值決策之能動性將加強發生於交界處與地標處之決策事件之權重，進而提升導航表現。此發生於交界處與地標處，或稱空間節點之編碼，提供了海馬迴神經細胞額外之權重，以編碼空間成為結構性之節點地圖。基於此假設，我們檢驗了於學習及提取期間，空間地圖於內部（自由導航）與外部（引導導航）產生之導航行為下之神經反應。我們招募了二十一位受試者於虛擬迷宮中分別進行自由導航、與引導導航之功能性磁振造影（fMRI）實驗。學習期間，於自由導航之情況下，受試者自由習得地標位置；於引導導航之情況下，受試者觀看影片引導其習得地標位置。提取期間，受試者判定目的地標之方向、距離、並且導航至目的地標始自不同之地點。我們觀察到於提取期間，引導導航相較於自由導航，受試者需花費更多時間導航至目的地標，並且展現更頻繁之失誤。關鍵腦區包含學習期間之輔助運動皮質區、與學習及提取期間之海馬迴，於自由導航之下，展現較引導導航下更高對於空間節點之神經反應；學習期間之顳中迴與提取期間之前、後扣帶迴皮質，於引導導航之下，展現較自由導航下更高對於空間節點之神經反應。特別來說，前海馬迴於學習期間自由導航下，展現較引導導航下更高對於空間節點之神經反應；後海馬迴則表現於提取期間引導導航下，較自由導航下更高由距離誤判比率調控對於距離判斷之神經反應。總結而言，我們展示於空間導航期間，價值決策能動性對於前海馬迴建構空間節點訊息之重要性。

Grid and place cell activity in the hippocampus (HC) instantiate cognitive map representations of space. In this study, we hypothesized that agency in navigational decision-making enhances navigational performances via emphasis on decision events at junctions and landmarks. Such coding of junctions and landmarks, or spatial nodes, provides HC neurons with additional weighting to encode plain space into structured node maps. To this end, we evaluated neural responses during learning and retrieving spatial maps under conditions of internally (Free) vs. externally (Tour) generated navigational movements. Twenty-one participants underwent functional magnetic resonance imaging (fMRI) spatial navigational experiments in virtual mazes under Free and Tour conditions. In the Free condition, participants learned landmark locations by free navigation. During retrieval, participants determined directions and distances and navigated to target landmarks from various start locations. In the Tour condition, participants viewed videos guiding them through the landmarks then did the same retrieval test. Navigation to target landmarks during retrieval took longer and failed more often for Tour than Free conditions. Critically, supplementary motor area responses during learning and HC responses during learning and retrieval to spatial nodes were higher for Free than Tour conditions. Middle temporal gyrus responses during learning, anterior and posterior cingulate cortex responses during retrieval to spatial nodes were higher for Tour than Free conditions. In particular, anterior HC responses to spatial nodes during learning were higher for Free than Tour conditions. In addition, posterior HC response modulation by distance mis-estimation during retrieval was greater for Tour than Free conditions. In sum, we demonstrate that agency in making navigational decisions is important for spatial node formation in anterior HC.