以實驗方法探究果蠅的時間感知

Abstract

為了瞭解在做決策時時間感知與時間折現的關係，我們使用果蠅作為實驗對象因其完善的基因工具可以幫助我們理解上述兩概念在神經活動上的關係。由於技術上的困難，本篇的實驗探究僅止於果蠅能否有時間感知能力的部分。我們試了多種的訓練方法，主要可以分為兩大類：古典制約學習以及操作制約學習。在古典制約學習的部分，我們採用經典的果蠅氣味學習實驗作為實驗設計的基礎。我們的實驗發現果蠅能夠依據提前給予的環境刺激(有無燈光)做出對應有獎勵的選擇。在探究時間區辨的能力上，我們用2秒鐘的連續光與10秒鐘的連續光作為時間指示刺激，發現果蠅有統計上顯著的學習效果。雖然訓練組和控制組的學習指數有統計上的顯著差異，但差異量過小促使我們選擇採用其他的方法進行訓練以提高學習效果。我們利用果蠅實驗光遺傳學的技術進行操作制約的訓練，我們訓練果蠅在行進間停下，並停下至少達到我們指定的秒數後而給予獎勵，藉此我們將指定秒數作為操縱變因試看各組間行為是否有差別。實驗結果發現我們的實驗組與控制組的行為並沒有統計上顯著的差異，也因此我們無法做出結論。

To understand the relationship between time perception and time discounting in decision making, we tried to use Drosophila Melanogaster as our animal model due to their well-developed genetic tools. We built up several training protocols for showing the existence of time perception in fruit flies. The protocols can be separated into two major part: Classical Conditioning and Operant Conditioning. In the classical conditioning protocol, we used the well-known odor association experiment as basis. We started from odor memory associated with two different interval timing stimuli. We showed that flies were able to perform context-dependent task with illumination changed context. We use 2 seconds and 10 seconds continuous light to represent the context of our first pair of interval timing task. The result showed marginally significant positive learning effect. However, as we changed to 1 second and 5 seconds pair, the result was no longer consistent. To enhance the learning performance, we have tried to use optogenetic tools to do operant conditioning to train flies to perform similar task. We trained the flies to use their motion as an operant that predicted the occurrence of reward. Every time an idle event was performed by flies, it would immediately trigger the occurrence of red light reward. The result showed that we were not able to conclude the flies learned to distinguish three different time intervals.