A neural circuit in the brain can be viewed as a primary functional gear set formed by interconnected neurons that communicate each other with chemical signals and electricity. To understand diverse brain functions, it could come down to two questions: what circuits are engaged by a specific function? What is the function of a specific neural circuit? Specific task or behavioral model relevant to specific behavioral function is required for scientists to map involved brain networks with activity-dependent targeting techniques. Then gain- and loss-of-function researches will be employed respectively to causally examine the ‘sufficiency’ and ‘requirement’ of the selective circuit in the behavioral function, which can be achieved by optogenetic techniques.

The mesolimbic dopamine (DA) system is essential to help establish incentive value for an otherwise neutral stimulus in acquisition of stimulus-reward associations. The development of conditioned approach behaviors is correlated to the appearance of burst firing activity of dopamine neurons to reward-predicting stimuli. How midbrain DA neurons are driven to become responsive to reward-predicting stimuli through Pavlovian conditioning remains unclear. Here, I will highlight how we combined optogenetic approach with in vivo recording technique and behavioral model to examine circuitry mechanisms of behavioral function.

近年來科技的發展，已經讓我們能夠在人類或動物身上，進行同步大規模的神經活性紀錄。甚至可以在動物清醒活動的情況下，精準的操弄神經迴路，來觀察其對動物行為造成的改變。儘管如此，我們對於大腦如何運作，特別在於高等認知功能方面，所知仍然極為有限。這其中的困難發生在哪裡？我將以視覺注意力的研究為例，討論哪些可能是關鍵、但卻仍然缺乏的要件，以及我們如何在要件未滿足的情況下，盡可能的去處理這樣的研究問題。