Behavioral procedures
This protocol is extracted from research article:
Indirect pathway from caudate tail mediates rejection of bad objects in periphery
Sci Adv, Aug 7, 2019; DOI: 10.1126/sciadv.aaw9297

Object-reward association learning task (Fig. 1A). This task was to let the subject learn the association of object with reward. This task procedure followed previous studies from the laboratory (24, 25, 28). In each trial, one object (out of eight objects) was presented, to which the subject made a saccade. This saccade was followed by a large or small reward, depending on the object value (good or bad). The subject learned the values of many objects in this manner (a total of 80 in ZB and a total of 48 in SP).

Passive viewing task (Fig. 1B). This task was used to investigate whether neurons encoded the values of individual objects more than 1 day after the object-reward association learning task. This task procedure also followed the previous studies (24, 25, 28). In each trial, several learned objects (one to six objects) were chosen pseudo-randomly and presented sequentially at a peripheral position (i.e., neuron’s receptive field) while the subject was fixating at the center. The trial ended with a reward, which, however, was not congruent with the presented objects. This task focused on the effect of object-value learning on neuronal responses before any behavioral response occurred.

Sequential saccade choice task (Fig. 2A and movies S1 and S2). This task was used to investigate both neuronal and behavioral responses during and after object-value learning. A set of eight objects were used in one block of 128 trials: four objects were associated with a large reward (good objects), while the other four objects were associated with no reward (bad objects) (Fig. 2A). In each trial, these objects were presented in a random sequence until the subject chose one (see below in detail). Each object appeared pseudo-randomly at one of four positions (up-right, down-right, up-left, and down-left) at 15° eccentricity from the center. After the subject fixated at a center green square for 700 ms, the fixation cue disappeared, and one object appeared. If the subject did not make a saccade to the object within 400 ms (i.e., made no choice), another object appeared after the same fixating period (see the first object in Fig. 2A). No choice trials were also deemed to occur if the monkey made a saccade to the presented object and then quickly (<400 ms) returned gaze to the center of the screen (see the second object in Fig. 2A). Conversely, a choice occurred if the subject made a saccade to the object within 400 ms and then gazed at it for 400 ms (i.e., choice), and the subjects received the outcome (reward or no reward) depending on the chosen object (good or bad) (see the third object in Fig. 2A). The next trial started after an intertrial interval of 1000 to 2000 ms. Overall, the subject learned to consistently reject bad objects before choosing a good object to get the reward.

Simultaneous saccade choice task (Fig. 4A). This task was used to investigate whether the pharmacological manipulation modulated the learned choices between good and bad objects that appeared simultaneously at different positions. The subject learned several object sets (ZB: three sets and SP: two sets) under the object-reward association learning task (Fig. 4A, top) before testing on the simultaneous saccade choice task (Fig. 4A, bottom). Each trial started with gaze fixation (700 ms) at a center magenta square. Then, the fixation cue disappeared and two randomly chosen objects (one good object and one bad object) appeared simultaneously. Their positions (15° from the center) were chosen pseudo-randomly from four combinations (up-left and down-left, up-right and down-right, up-left and up-right, and down-left and down-right). When a saccade occurred to any of the two objects, these objects turned to white squares immediately (Fig. 4A, bottom). After gazing at either square for 600 ms, a large or small reward was delivered depending on the subject’s choice (good or bad object). In each block of trials, one set of eight learned objects was used.

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