For each novel symbol, we calculated the number of trials needed for the behavioral value to reach 95% of the actual value by finding the bin number where the fitted exponential curve crossed 95% of the actual value. As an alternative method of calculating how long it took each monkey to learn each novel symbol, we calculated a running average of the frequency Pictilisib ic50 of larger choices for each novel symbol by averaging across a moving window of ±10 consecutive trials; using only trials in which the novel symbol was one of the options. We calculated how many trials it took each monkey to attain 90% correct

(larger) choices for each novel symbol. Results were almost identical to the equivalent value calculations described above, in that the adults took more trials to learn each novel symbol than the juveniles did. We tested all the monkeys behaviorally with 1.5- and 2-fold larger and smaller fonts, for which they maintained the same accuracy as with the original size. We tested the monkeys behaviorally using a serif font (Utopia), instead of the sans serif font (Helvetica) they first learned, and they all recognized this font accurately after a few days. Six monkeys were scanned to look for localization of Learned symbol responsiveness: two adults (one male and one female) who had learned symbols, three juveniles

who had learned symbols, Quizartinib and one adult male who had not been exposed to the symbol task. These six animals represent the maximum number of our trained monkeys who could be scanned; the fourth trained juvenile and the other adult female were not willing to sit still enough in the scanner for fMRI, and the other trained adult males are too large to scan. The monkeys were scanned using techniques similar to those pioneered by Vanduffel and colleagues (2001). The monkeys lay comfortably in a horizontal primate chair in a “sphynx” position, free to move PDK4 limbs, but with the head restrained.

The heads of four of the monkeys (the adult female and the three juveniles) were held stationary during scanning using a noninvasive vacuum helmet restraint (Srihasam et al., 2010), and the two adult males were held still using previously implanted delrin headposts (Tsao et al., 2006 and Vanduffel et al., 2001). Each monkey was trained to sit in the chair and habituated to the sounds of MR scanning in a “mock” MR bore. The monkeys were water scheduled during the period of testing, and behavioral control was achieved using operant conditioning techniques. They were trained on a fixation task, and eye position was monitored using a pupil-corneal reflection tracking system (RK-726PCI, ISCAN, Cambridge, MA). Monkeys were rewarded for maintaining fixation within a 2° square fixation window.