To tackle this question, researchers needed to induce a fear response in subjects in the lab. Merel Kindt and his team gave a mild electric shock to participants, while they were shown pictures of spiders — this produced a kind of Pavlovian pairing between two stimuli. They determined the physiological fear response in each participant by measuring how much his or her eyes blinked when shown a picture of the spider by itself. This method is actually a measure of how much the amygdala, the hub of emotion, reacts to the stimulus. When the pictures by themselves elicited the blink response, the researchers considered the memory of the fear to be "consolidated", meaning that the reaction was remembered and would be evocable at a later time.
This method is actually a measure of how much the amygdala, the hub of emotion, reacts to the stimulus.