Researchers can examine the biological basis of fear, smell, memory, and diseases by using what technique?

The correct answer is - optogenetics.

Explanation:

Optogenetics is a technique that is used in examining the basis of smell, fear, and memory that involves the use of light to regulate cells in a biological tissue especially neurons, which are genetically altered to show light ion channels.

Channelrhodopsin-2 is the most commonly used ion channel for triggering the optogenetics. When a definite number of positive ions have to get through the cell membrane, it causes the neuron to fire reaching the threshold.

Thus, the correct answer is - optogenetics.

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