Microinjections of the dopamine agonist apomorphine into the nucleus basalis prosencephali of pigeons elicit stereotyped pecking behaviour. Injections of 6-hydroxydopamine, a toxic dopamine antagonist, into the same nucleus impair stereotyped pecking induced by systemic apomorphine administration, but do not interfere with pecking in the normal feeding context.

Pigeons that repeatedly experienced the effect of apomorphine in the same environment showed an augmented behavioural response to the same drug dose as compared with controls that experienced the effect of the drug dose in differing environments. Sensitization, an increase in the behavioural response that is observed in pigeons when the same dose of apomorphine is repeatedly administered, may thus be mainly due to a conditioning of the drug response to incidental environmental cues. Apomorphine injections also induced place preferences. Pigeons that had experienced a particular environment under the influence of apomorphine subsequently favoured that environment to one they had experienced while under saline. This suggests that apomorphine administration has reinforcing properties for birds, much as it has for mammals.

Abstract. The dopamine agonist apomorphine elicits protracted pecking when injected systemically (1 mg/kg) into pigeons. In two experiments it was investigated whether apomorphine would function as an unconditioned stimulus in the classical conditioning of pecking in these animals. An experimental design based on a differentiation procedure was used so that possible pseudoconditioning effects were controlled. Two differently coloured test chambers served as negative (CS-) and positive conditioned (CS +) stimuli. During the training phase the subjects experienced the former while injected with saline, and the latter while injected with apomorphine. In later tests not involving any injections the pigeons made significantly more pecks (conditioned response) in the CS+ chamber than in the CSchamber. In the first and second experiments the conditioned stimuli were, respectively, discrete and diffuse visual cues, but both had similar effects. The conditioning obtained may explain sensitization effects that are observed with repeated apomorphine injections. Apomorphine probably also functions as a positive reinforcer for instrumental conditioning in pigeons.

The feature-positive effect (FPE) is a widespread and robust phenomenon in the context of discrimination learning. It refers to the fact that a distinctive feature associated with a stimulus that is reinforced leads to efficient discrimination learning, whereas the same feature associated with the nonreinforced stimulus inhibits discrimination learning. Two experiments with pigeons showed that the FPE also occurs with a simultaneous discrimination paradigm involving brief discrete trials and no intertrial intervals. A pre-training treatment unexpectedly prevented the expression of the FPE in this discrimination task. The pretraining consisted of having pigeons discriminate the feature/nonfeature visual shapes from a plain background disc. Rewarding responses to the shapes, or alternatively to the blank disc, had the same FPE-preventing effect. A reversal of a feature/nonfeature stimulus discrimination led to an analogous erasure of the FPE. The results are discussed in terms of the concurrence or interference between the various associations that the subjects formed on the basis of the different stimulus-reward correlations they experienced in the different phases of the experiments.

The electrocardiogram of pigeons was recorded while they pecked an impact transducer under operant control according to a variable ratio schedule. An analysis of the records in terms of crossaverages between heart beats and pecks. the quasi-equivalents of crosscorrelation functions, revealed that pecks and heart beats tend to coincide temporally at above chance levels according to patterns that vary from individual to individual pigeon. The mechanisms and the functions of the coupling are discussed. .. Experimentelle Tierpsychologie. Psychologisches Institut. Ruhr-Universitat Bochum. D 4630 Bochum. FRG