Fig. 4.

A cellular memory trace in the MB neurons is localized to the vertical branch. The optical reporter G-CaMP was expressed in both the α (vertical) and the β (horizontal) branches of the MB neurons. Flies were conditioned in a behavioral apparatus such that they received either an odor paired with shock (CS+) or an odor not paired with shock (CS−). Forward conditioning, in which the CS + and the shock were presented simultaneously, was spread over multiple, spaced trials to generate long-term memory. As a control, backward conditioning, in which the CS+ loses its predictive value because it is delivered at the end of the shock presentation, was also tested. Twenty-four hours post-conditioning, the reporter’s response to both the CS+ and the CS− odors was measured and quantified as the percentage change in fluorescence. A significant increase in reporter activity was observed only in response to forward conditioning with the CS+ odor and only in the α branch of the MB neurons. Adapted with permission from Yu et al. (2006).