Emergence of interoceptive and exteroceptive control of behavior in rats

The role of exteroceptive and interoceptive aversive stimuli in rats 2 to 14 days old was investigated according to an odor aversion paradigm. Amyl acetate odor was paired with either peripheral shock, intraperitoneal shock, or lithium chloride poisoning. Intraperitoneal shock was an effective unconditioned stimulus at all ages and produced odor aversions comparable to lithium chloride poisoning; peripheral shock, however, was effective only in rats 10 days of age or older. Interoceptive control of aversively motivated behaviors thus seems to develop before exteroceptive control, and the failure of previous studies to find reliable learning and retention of shock-motivated behaviors before 8 to 10 days of age may be attributable to the site to which shock was applied rather than to insensitivity to shock per se.