Behavioral Training

Jin and Costa, 2010 Jin X.

Costa R.M. Start/stop signals emerge in nigrostriatal circuits during sequence learning. Jin et al., 2014 Jin X.

Tecuapetla F.

Costa R.M. Basal ganglia subcircuits distinctively encode the parsing and concatenation of action sequences. Behavioral training took place in operant chambers (Med Associates) which were placed inside a sound attenuating box. Behavioral chambers were 21.6 cm L × 17.8 cm W × 12.7 cm H and were comprised of a central food magazine with retractable levers on both sides. A house light (3 W, 24 V) was centered near the ceiling on the opposite side of the food magazine (). Sucrose solution (10%, 10 μL) was delivered into a bowl in the food magazine by a syringe pump. Operant chambers were computer controlled and all behavioral programs were custom written. Mice were food restricted for at least 24 hr prior to training and were maintained at ∼85% free-feeding weight by providing ∼2.5 g regular chow per day per mouse.

Behavioral training began with 60 min continuous reinforcement (CRF) training, where mice were presented with either the left or the right lever which resulted in one reward each time the lever was pressed. Sessions began with illumination of the house light and extension of either the right or left lever. The first day, mice received 5 reward on each lever. The second day, mice received 10 reward on each lever. The third day, mice received 15 reward on each lever. Lever presentation order was counterbalanced and following completion of the task levers were retracted and the house light was turned off.

Church and Deluty, 1977 Church R.M.

Deluty M.Z. Bisection of temporal intervals. Following the completion of CRF, mice were trained on an adopted version of a temporal bisection task ( Figure 1 A), where they were trained to discriminate two time intervals and respond on either the left or right lever accordingly (). Sessions began with illumination of the house light and extension of both the left and the right levers. Following a random interval which ranged from 30–40 s (35 s on average), two levers were retracted for either 2 or 8 s (50% chance of either interval, random order). Both levers were then extended and the first response on the left lever following a 2 s retraction interval or the first response on the right lever following an 8 s retraction interval resulted in reward delivery. For a subgroup of experiments, the contingency between time interval and lever pressing was reversed, i.e., 2- and 8-s trials were rewarded following right or left lever responses, respectively. Only the first press on the correct lever following lever extension could result in reward, that is, mice were not rewarded with any further lever pressing after making an incorrect choice or by continuous responding on the correct lever. The inter-trial-interval period with both levers extended thus served as an extinction test for reading out the animal’s net preference. Behavioral sessions were terminated after 180 min or following 160 rewards, whichever happened first. Mice that were included in voltammetric or electrophysiological studies were trained to ≥ 75% accuracy before implanting recording electrodes. Following surgery, mice were trained back to ≥ 75% accuracy before physiological recordings took place. For all tasks, mice that needed to be attached to cables for stimulation or recording were trained with cables attached through the post-surgery period to allow better habituation to the weight of the headstage.

Mice previously trained on 2 and 8 s discrimination were later trained on 4 and 16 s discrimination ( Figure 3 A). These trials were in the same structure and contingency as the 2-8 s task, the only difference being that lever retraction intervals were doubled.

Mice previously trained on 2 and 8 s discrimination were later tested using unrewarded 16 s probe trials ( Figure 3 G). Here, trials were identical to those described above except that 10% of trials were comprised of 16 s retraction intervals which remained unrewarded irrespective of the animal’s choice. The other 90% of trials were 2 and 8 s retraction intervals (45% each) with maintained normal action-reward contingency. These trials were presented in a random order.

A separate group of naive mice that had not been trained on the 2-8 s task were utilized for the 2-8 s Pavlovian task. Here, mice were initially trained on CRF, as described above. Next, mice were trained on a task with 2 and 8 s lever retraction intervals, but where reward was delivered at lever extension regardless of response ( Figure 4 A). Sessions began with illumination of the house light and extension of both the left and the right levers. Following a random interval which ranged from 30–40 s (35 s on average), two levers were retracted for either 2 or 8 s (50% chance of either interval, random order). Both levers were then extended and a sucrose reward was delivered.

Mice previously trained on the 2-8 s Pavlovian task were then trained in the 2-8 s forced choice task. This task had an identical structure as the 2-8 s task, but mice only received reward by selecting the left lever following retraction periods ( Figure 4 D). Following a random interval which ranged from 30–40 s (35 s on average), two levers were retracted for either 2 or 8 s (50% chance of either interval, random order). Both levers were then extended and selection of the left lever resulted in delivery of a sucrose reward. Only the first left press following extension yielded reward and right lever presses and repetitive pressing at the left lever had no effect.

For the task with 100% 8-s trials, the task structure was exactly the same as 2-8 s task, but 2-s trials were completely omitted ( Figure 4 G). Mice therefore only experienced 8-s trials the whole session and received reward on the right lever following 8 s lever retractions. Left lever presses and repetitive responding on the right lever were unrewarded. Mice were trained on this task until they achieved an accuracy of ∼95%. Voltammetric recordings in this task were collected from one subgroup of mice previously trained on 2 and 8 s discrimination, as well as a separate group of naive animals trained only on 100% 8-s trials. Data from these two groups were consistent and were therefore combined.

A separate group of naive mice that had not been trained previously were used in the 2-8 s tone task. Here, a task with identical structure to the 2-8 s task was used, but where two different tones indicated appropriate behavioral response (left or right lever selection, Figure 4 J). Sessions began with illumination of the house light and extension of both the left and the right levers. Following a random interval which ranged from 30–40 s (35 s on average), two levers were retracted for either 2 or 8 s (50% chance of either interval, random order). Then, one second prior to lever extension, either a 3,000 or 10,000 Hz tone was played. Following lever extension in trials with a 3,000 Hz tone, a left lever press yielded a single sucrose reward whereas repetitive responding or right lever presses yielded no reward. Conversely, following lever extension in trials with a 10,000 Hz tone, a right lever press yielded a single sucrose reward whereas repetitive responding or left lever presses yielded no response. Only the first response following lever extension could result in reward. Mice were trained 2-3 weeks to reach ≥ 70% correct rate before recordings occurred. One group of mice was trained prior to voltammetric implantation and another was trained previous to implantation. Recordings from these groups did not differ significantly and were combined. To increase numbers of rewarded trials, mice could earn up to 250 reward during recordings.

Church and Deluty, 1977 Church R.M.

Deluty M.Z. Bisection of temporal intervals. Learning curves for both wild-type and KO animals were determined by first training mice on CRF as described above. Once they met CRF training criterion, mice were trained daily on 2 and 8 s lever retraction discrimination with sessions lasting 180 min or until mice received 160 rewards. The training lasted 14 days. Accuracy was defined as percentage of correct trials. Psychometric curves were constructed using unrewarded probe trials after these 14 days of training. Here, mice were presented with unrewarded probe trials with retraction intervals of 2.5, 3.2, 4, 5, or 6.3 s in duration. These probe trial durations represent evenly spaced intervals between 2 and 8 s on a logarithmic scale, as temporal bisection is thought to fall at the logarithmic, rather than arithmetic, mean of the intervals tested (). These probe trials were randomly presented and comprised 30% of all trials, with the remaining 70% of trials being 2 or 8 s in duration (35% each). Mice were tested on the first, third, fifth, and seventh day following 14 day training. On the second, fourth, and sixth day following training, mice were retrained on the 2-8 s task without probes. All probe trials were not rewarded irrespective of the animal’s choice.

Both wild-type and KO mice used for physiological experiments were trained for two weeks on 2 and 8 s discrimination as described above prior to implantation of recording electrodes. Following recovery, mice were again food restricted and retrained to ∼75% accuracy, or, in the case of RGS-NR1 KO mice, for one additional week prior to recording sessions.