Figure 1.

Task, behavior, and recording sites. a, The sequence of events in each trial block. At the beginning of each recording session, one well was arbitrarily designated as short (a short 500 ms delay before reward) and the other designated as long (a relatively long 1–7 s delay before reward) (block 1). After the first block of trials (∼60 trials), the wells unexpectedly reversed contingencies (block 2). With the transition to block 3, the delays to reward were held constant across wells (500 ms), but the size of the reward was manipulated. The well designated as long during the previous block now offered two fluid boli whereas the opposite well offered one bolus. The reward contingencies again reversed in block 4. b, c, Height of each bar indicates the reaction time (port exit minus odor offset) and percentage correct for short (black), long (light gray), big (dark gray), and small (white) forced-choice trials for young and aged rats. d, The height of each bar indicates the percentage choice of short-delay (black) and big-reward (dark gray) taken over all free-choice trials. e, Latency to nose poke after onset of house lights during the first and last five trials in each block for aged (circles) and young (squares) rats. Asterisks, planned comparisons revealing statistically significant differences (t test, p < 0.05). Error bars indicate SEs. #, main effect of age in ANOVA. f, g, Recording sites for each rat. Gray dot represents the final position of the electrode as verified by histology. Box estimates the extent of the recording over all rats.