當動物進行目標導向的動作時,需要藉由角度路徑積分來維持空間中的方位,近期研究
發現果蠅的橢圓體 (ellipsoid body, EB) 有著能夠維持自身空間方位的功能,但詳細的神經迴路
以及工作機制仍然不明。於本研究中,我們跟據近期有關中央複合體 (central complex) 的解
剖學研究建立了 EB 與 protocerebral bridge (PB)的神經迴路模型,該模型是由四種神經類組
成兩個耦合的復發迴路,我們的分析發現其中一個 C 環復發迴路可以藉由對稱環形成很強的局
部回饋;而另一個 P 環復發迴路則是有著非對稱環。經電腦模擬展示兩個環迴路的相異的功能,
C 環迴路能夠維持穩定的活性區域 (activity bump) 並表示著顯著視覺記號的方位,就算視覺記
號消失後依然維持著;而 P 環迴路能夠在沒有視覺記號下經由 PB 接收半側的刺激來偏移活性
區域,我們認為 P 環迴路是能夠對角度路徑積分的,而活性區域的偏移表示著果蠅能夠在黑暗
中旋轉身體並維持空間方位。更進一步的神經體 (connectome) 分析說明有著重力感知神經的
聽覺系統可能能夠給予 PB 半側的刺激。該模型重現了數個被觀察到在 EB 的關鍵活動特徵並能
夠提出實驗可試驗的預測,並對細胞如何維持空間方位的資訊並且追蹤提出了新的觀點。

Maintaining spatial orientation when carrying out goal-directed movements
requires an animal to perform angular path integration. Such functionality has been
recently demonstrated in the ellipsoid body (EB) of fruit flies, though the precise circuitry
and underlying mechanisms remain unclear. In the present study, we proposed a
spiking neural circuit model of the EB and the protocerebral bridge(PB) based on recent
anatomical studies of the central complex. Our data-driven model describes two
coupled recurrent circuits formed by four classes of neurons. Our analysis showed that
one recurrent circuit, the C ring, forms strong local feedback with a symmetric ring while
the other recurrent circuit, the P ring, is characterized by an asymmetric ring. Computer
simulations demonstrated distinct functions performed by the two ring circuits. The C
ring circuit was able to sustain a stable activity bump that represents the orientation of a
salient visual cue and the bump persisted after cue offset. The P ring circuit, on the
other hand, shifted the activity bump in the absence of the visual cue when the PB
receives a unilateral input. We argued that P ring circuit is capable of integrating the
angular path and this bump shifting function represents the ability of the fly to maintain
spatial orientation when it rotates in the dark. A further connectome analysis indicated
that the auditory system, which hosts the gravitational sensory neurons, may provide
the unilateral input to the PB. The present model reproduces several key features of the
EB activity and makes experimentally testable predictions, providing new insight into
how spatial orientation is maintained and tracked at the cellular level.

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