Figure 1.

Schematic of delayed response working memory task. Each trial of the delayed response task includes three phases. During the sample phase, one lever (left or right, pseudo-randomly varied between pairs of trials) is extended into the chamber. The rat must press the extended lever to enter the variable duration “delay phase” (delays are pseudo-randomly varied from 0 to 24 s within each block of seven trials). During the delay, the rat must nose poke continuously into the centrally located food trough. The first nose poke emitted after the expiration of the predetermined delay timer initiates the choice phase wherein both levers (left and right) are extended into the chamber. The rat must remember and press the same lever that was extended during the sample phase to receive a food reward (a 45-mg food pellet), and this is scored as a correct choice. Pressing the other lever is scored as an incorrect choice and no food reward is delivered.