Experimental methods.

<p>A. Timeline. B. Sequential steps in carrying out the within-litter neonatal novelty exposure procedure: (i) Dam is removed from the home cage; (ii) Novel pups are transferred to individual non-home cages and yoked Home pups receive a matching amount of experimenter contact; (iii) After 3 min in the non-home cages, Novel pups are returned to the home cage in which the Home pups remain; (iv) Dam is returned to the home cage. C. Apparatus used to assess rats' ability to compete against a conspecific for exclusive access to chocolate rewards. Note that the runway was sufficiently narrow as to allow only one rat at a time to fully enter.