為了在複雜環境中導航，動物需要具備空間方向感。許多研究表明，果蠅橢圓體(ellipsoid body, EB)腦區上的神經活性反映出活躍區(activity bump)，形成一個頭向系統。但是，活躍區如何維持穩定和持續更新角度，其中的機制尚不明瞭，為了探討此問題，我構建出一個馬可夫鏈行為模型，結合先前已建立之前橋腦(protocerebral bridge, PB)-橢圓體神經網路模型，並根據近來釋出的電子顯微鏡果蠅神經體資料進一步調整架構和參數，再以此進行模擬來解釋基於布利丹效應之空間方向記憶行為實驗結果。實驗中，藉由基因調控或光遺傳學方式去抑制、活化兩種抑制性環形神經元：EIP環神經元、P環神經元，進而觀察二者對於空間方向記憶的影響。最終，前橋腦-橢圓體神經網路模型推論：EIP環神經元是維持活躍區形狀的關鍵因素，而P環神經元則負責控制果蠅身體旋轉時活躍區相應的更新。

To navigate in a complex environment, an animal needs to keep track of its orientation. Many studies revealed that a bump of activity in the Drosophila ellipsoid body (EB) represented head-direction. However, how the activity bump maintains stability while constantly updates its representation is not completed understood. To address this issue, I constructed a Markov-chain behavior model and combined it with a previously developed neural circuit model of protocerebral bridge (PB) and EB. I modified the neural circuit model based on the latest electron microscopy data and performed parameter tuning. The model was used to elucidate the results of behavioral experiments based on a modified Buridan’s paradigm. In the experiments, roles of specific neurons in orientation working memory were observed by silencing or optogenetically activating two types of inhibitory ring neurons: EIP-ring neurons and P-ring neurons. The model suggested that the EIP-ring neurons are crucial for maintaining the shape of the activity bump in EB, while the P-ring neurons are responsible for controlling the updating process for the bump location when a fly rotates its body.

一、 簡介 …………………………………………………………………………………… 1

二、 方法 …………………………………………………………………………………… 5
(一)、 PB-EB神經網路模型 ………………………… 5
(二)、 神經元及突觸模型 ………………………… 10
(三)、 行為實驗與馬可夫鏈行為模型 ………………………… 12
(四)、 環形神經元調控與其他模型參數 ………………………… 16
(五)、 取得電子顯微鏡果蠅大腦資料 ………………………… 16

三、 結果 …………………………………………………………………………………… 17
(一)、 模擬野生型果蠅之行為 ………… 17
(二)、 模擬EIP環、P環神經元抑制 ………… 20
(三)、 模擬EIP環、P環神經元於刺激階段活化 ………… 22
(四)、 模擬EIP環、P環神經元於後刺激階段活化 ………… 25
(五)、 以電子顯微鏡資料修正PB-EB模型 ………… 26

四、 討論 …………………………………………………………………………………… 29

五、 參考文獻 …………………………………………………………………………… 32

六、 附錄 …………………………………………………………………………………… 35

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