Activation of the central serotonergic system in response to delayed but not omitted rewards.
Bottom Line: The forebrain serotonergic system is a crucial component in the control of impulsive behaviours.By contrast, during the intermittent reward condition, in which food was given on only about one-third of the site visits, the level of dopamine was lower than that during the immediate reward condition, whereas the level of serotonin did not change significantly.This is the first direct evidence that activation of the serotonergic system occurs specifically in relation to waiting for a delayed reward.
Affiliation: Neural Computation Unit, Okinawa Institute of Science and Technology, Onna, Okinawa, Japan. email@example.comShow MeSH
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Mentions: Among the six rats, three of them were tested with sequence 1 on the first day and sequence 2 on the following day. Three others were tested in the counterbalanced order. We excluded the measurements in which the 5-HT or DA concentration data were smaller than signal-to-noise ratio 3. From this procedure, we obtained 10 task sequence data for 5-HT (5 from sequence 1 and 5 from sequence 2) and 8 task sequence data for DA (4 from sequence 1 and 4 from sequence 2). Probe placements within the DRN are shown in Fig. 2. The numbers of food pellets (mean ± SEM) obtained during the 30 min periods were 56.5 ± 6.5 (n=10) in the immediate reward condition, 37.7 ± 4.5 (n=10) in the delayed reward condition, and 14.8 ± 1.4 (n=10) in the intermittent reward condition (Fig. 3A). These differences are due, at least in part, to the time spent waiting in the delayed reward condition and the omission of the rewards in the intermittent reward condition. The total traveling distance during the 30 min period was significantly shorter in the delayed reward condition than in the other two conditions (paired t-test, immediate vs. delay P=0.011; immediate vs. intermittent, P=0.24; delay vs. intermittent, P=0.0011) (Fig. 3B), again partly due to the time spent waiting at the reward sites. Movement toward the reward sites was quickest during the immediate reward condition and slowest in the intermittent reward condition (paired t-test, P=0.0015 for time to food site; P=0.027 for time to water site) (Fig. 3C and D), suggesting the highest motivation in the immediate reward condition and the lowest motivation in the intermittent reward condition.
Affiliation: Neural Computation Unit, Okinawa Institute of Science and Technology, Onna, Okinawa, Japan. firstname.lastname@example.org