Memory formation in birds: 2. Effects of stress due to experimental procedures on the conditioning of the budgerigar (Melopsittacus undulatus) to sound stimuli.
Conditioning studies involving administration of biochemical or pharmacological agents are often stressful to experimental animals. Some of these stressful manipulations were examined for their effect on the avoidance conditioning of the budgerigar to sound stimuli. There were individual variations in the capacity of the birds to accommodate to these stresses, but generally the stress factors had negative effects on their subsequent conditioning, the degree of this effect depending upon the type and severity of stress. Simple anesthesia with ether had the least effect, intravenous injection being next in severity, while intracerebral injection was most inhibitory. The effects due to anesthesia and intravenous injection could be decreased by delaying the conditioning procedure for 1 to 2 hours following the treatment, but the effect of intracerebral injection was more prolonged. The retrieval of temporarily lost conditioned response through brief reconditioning was not affected by intracerebral injection, indicating that, once a memory trace was formed, subsequent emotional and physical stresses did not obliterate it irreversibly.