TITLE: Delay Discounting Task
AUTHORS: Xiaowen Zhuang, Alexandra Nelson

[DESCRIPTION]
This protocol details the Delay discounting task.

[GUIDELINES]
This protocol can be used after following the Basic Operant Training protocol listed separately. That protocol includes information about operant box design and implementation, as well as the first three phases of training, prior to using the Delay Discounting Task (detailed here). 

[STEPS]
SECTION: Setup
1. Refer to Basic Operant Training Protocol.
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
2. Each session contains three trial types: forced choice delayed/large, forced choice immediate/small, and free choice.
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
3. Each session contains four blocks, each using a different delay time. 
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
4. Each block includes 30 trials (5 forced choice delayed/large trials, 5 forced choice immediate/small trials, and 20 free choice trials). 
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
5. The first 10 trials are meant as a “refresher”, orienting the mouse to the delays and rewards associated with each choice port in that block, while the latter 20 trials are designed to reflect an animal’s preferences between small/immediate versus delayed/large rewards).
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
6. In a given mouse, the left and right sides are assigned to either delayed/large or immediate/small outcomes, but the side assignments are randomly distributed between mice. 
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
7. Each trial has a fixed duration of 50 s.

SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
8. All trials start with a 10-second illumination of the center port light.
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
9. A center nosepoke within 10 s extinguishes the light and initiates the trial. 

SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
10. Trials on which mice fail to nosepoke during this window are recorded as center omissions.
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
11. During forced choice delayed/large trials, cue lights on one side are illuminated for 10 s, and a nosepoke at that port results in a large reward (15 µL) being delivered to the center port after a delay period, as described below.

SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
12. During forced choice immediate/small trials, cue lights on the other side are illuminated for 10 s signaling, and a nosepoke at that port results in a small reward (5 µL) delivered to the center port immediately.

SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
13. During free choice trials (see Figure 1), both left and right cue lights are illuminated for 10 s.

 
 
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
14. Nosepokes on either side result in a reward, following the contingencies introduced during the "refresher" trials. 
SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
15. The delay preceding large reward delivery increases across a session (between blocks) from 0 seconds (block 1) to 3 s (block 2), to 6 s (block 3), to 9 s (block 4).

SECTION: Phase 4/Delay Discounting (10 - 15 sessions)
16. If a mouse fails to nosepoke in one of the side ports within 10 s, the cue lights are extinguished, and the trial is recorded as a side omission.

SECTION: Data collection and analysis
17. 
 

The mouse’s choice of either large or small reward-associated ports during free trials. This is typically the primary outcome measure in delay discounting.
SECTION: Data collection and analysis
18. Time of center light on.
SECTION: Data collection and analysis
19. Time of center nosepoke (combined with above, can calculate the reaction time).
SECTION: Data collection and analysis
20. Time of left or right nosepoke after the side cue lights illuminate (combined with above, can calculate choice reaction time).
SECTION: Data collection and analysis
21. 
 

Reaction time from the beginning of the trial (center nosepoke time minus trial initiation time), which may reflect attention and motivation.
SECTION: Data collection and analysis
22. Choice reaction time (left/right nosepoke time minus center poke response time), which can reflect motivation regarding specific choices or within blocks.