感官訊息可藉由不同強度的刺激進而產生不同的感覺或行為反應，暗示外界的訊息藉由腦內神經網路將單一訊息由具有重疊性和專一性的第一層感官神經接收，再傳遞到下一階層的不同神經網路到更高層的腦神經中心。果蠅利用特定的第一層嗅覺神經元 (olfactory sensory neurons)來偵測環境的二氧化碳，並將二氧化碳的訊息傳遞到腦內第一層嗅覺中心-嗅葉 (Antennal lobes)，接著分別由不同種型態的嗅覺投射神經元 (projection neurons)把接收到的訊息分別傳遞至腦內不同的更高層腦神經中心。此實驗中，我們主要發現果蠅利用腦內一系列複雜神經網路的轉軌機制，進而區分環境不同濃度的二氧化碳。 目前我們發現有兩種不同的神經迴路-分別為PNv-1和PNv-2神經迴路分別參與低濃度和高濃度下二氧化碳引發的躲避行為。低濃度的二氧化碳啟動PNv-1的單一神經迴路，相反的高濃度的二氧化碳會啟動全部PNv的神經迴路。然而在高濃度的二氧化碳下會啟動第三種類的PNv-抑制性的PNv-3 神經元，這一類神經元會抑制PNv-1神經迴路所產生的躲避行為。此實驗結果讓我們更進一步了解神經網路是如何在單一外界感官刺激下藉由不同的濃度或是在不同的狀況下藉由調節神經網路活性，讓外界感官訊息可以在神經網路間進行轉軌，最後產生適當的行為表現。

Different stimuli intensities elicit distinct perceptions or responses, implying that input signals are either conveyed through an overlapping but unique sub-population of sensory neurons or channeled into divergent brain circuits according to intensity. Carbon dioxide (CO2) is detected by a single type of olfactory sensory neuron (OSN) but is conveyed to higher brain centers through a diverse assortment of second-order projection neurons (PNs). We identified the circuitry that mediates Drosophila avoidance to different CO2 concentrations. Two distinct pathways, PNv-1 and PNv-2, are necessary and sufficient for avoidance responses to low and high CO2 concentrations, respectively. Low concentrations only activate PNv-1, but high concentrations activate both PNvs. However, high CO2 concentrations also activate a third PNv class, the γ-aminobutyric acid (GABA)ergic releasing PNv-3 neurons, which may inhibit PNv-1 pathway-mediated avoidance behavior. A circuit configuration that channels a common sensory input into distinct neural pathways would allow the perception of or the response elicited by a given odor to be further modulated by both stimulus intensity and context.

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