Answer to Question 1
Answer: Brain cells require glucose as fuel for activity. 2-DG, like glucose, is taken up into neurons, but cannot be used for energy. If a radioactive version of 2-DG is injected into an animal, radioactive 2-DG molecules will accumulate in the brain as a function of the relative activity of those cells. Autoradiography will reveal the presence of radioactive molecules in the brain, with a more intense signal in regions that were more active and a less intense signal in less active regions.
Answer to Question 2
Answer: The method can be used to stimulate or inhibit neurons in a specific brain region. Two distinct photosensitive proteins have been identified. ChR2 controls a sodium channel and is sensitive to blue light. NpHR controls a chloride channel and is sensitive to yellow light. The proteins are inserted into a brain region and the response to blue or yellow light is noted. Typically, blue light activates and yellow light inhibits neuron activity.
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