Objects never experienced before by 4 groups of monkeys were introduced into a free operant chain manipulation situation. The presence of the objects disrupted the manipulation response rates of 2 groups of animals differing in age and onset of a diet restricted in protein. Age controls receiving higher concentrations of protein in diets isocaloric with respect to the protein restricted diet, showed increased performance to these stimuli. The reinstatement of the chains alone condition resulted in a partial, but temporary recovery, of the manipulation response by low protein animals. This disruption in chain pulling behavior by malnourished monkeys may be similar to neophobic avoidance reactions previously observed in protein deprived monkeys.
Decreased investigative behavior has long been considered one of the persistent features of protein-calorie malnutrition (PCM) in humans. Children suffering from this disease often appear lethargic, apathetic, withdrawn, and inert (Jelliffe & Welbourn, 1963). Similar psychomotor changes have been reported for infrahuman organisms. Frankova and Barnes (1968) found the frequency of exploratory-like behavior in malnourished and previously malnourished rats to be significantly below that of normal controls. This decrement in exploratory behavior was not merely a decrease in general activity because malnourished rats did not differ significantly from controls in horizontal movements. Kerr and Waisman (1968) observed apathetic behavior patterns and retarded social development in protein malnourished infant monkeys. In a study of puzzle solving behavior, young monkeys subjected to protein deprivation solved fewer puzzles and had lower rates of manipulation than well fed animals (Strobe1 & Zimmermann, 197 1). However, in that experiment secondary infectious diseases associated with malnutrition may have contributed to these results. Similar deficits in manipulatory responsiveness have been found in year-old monkeys placed on diets deficient in protein (Zimmermann & Strobel, 1969). The animals showed a rapid