To investigate the neural basis of socio-economic behaviors in birds, we examined the effects of bilateral electrolytic lesions of arcopallium (Arco, the major descending pallial area of the avian telencephalon) and the surrounding nuclei in domestic chicks. We tested foraging effort (running distance) in an I-shaped maze with two food patches that delivered food in a biased manner according to a variable interval schedule. Normally, chicks run back and forth between the patches, and the patch use time matches the respective food delivery rate. In the paired phase, even without actual interference of food, chicks showed social facilitation of running effort compared with the single phase. Chicks with lesions in the Arco and lateral Arco showed significant reductions in social facilitation. The lesion effects of the lateral Arco were particularly selective, as it was not accompanied by changes in running distance in the single phase. Lesions of the nidopallium and nucleus taeniae of the amygdala produced no changes in foraging behavior. On the other hand, the Arco lesion did not impair social facilitation of operant peck latency. In accordance with this, anterograde tracing revealed characteristic projections from the lateral Arco to the extended amygdala, hippocampus, and septum, as well as wide areas of limbic nuclei in the hypothalamus and medial areas of the striatum including the nucleus accumbens. Pathways from the lateral Arco could enable chicks to overcome the extra effort investment of social foraging, suggesting functional and anatomical analogies to the anterior cingulate cortex and basolateral amygdala in mammals.

15Previous studies have shown that domestic chicks, Gallus gallus domesticus, trained in 16 a competitive foraging condition would subsequently develop a high degree of 17 impulsiveness in an intertemporal choice paradigm. Competition inevitably causes 18 variance in the amount of food that the foragers gain. However, it is not known whether 19 the food variance is causally linked with the impulsiveness. In experiment 1, we 20 compared four groups of chicks trained in combinations of two social conditions 21 (pseudocompetition or isolated) and two food conditions (variable or constant food). 22The food variance was introduced by varying the number of grains in each trial 23 according to a binomial distribution. The subject chick was separated from the 24 コメント [AT1]: Author: 'variant' means 'different'. I think you mean 'variable'.2 competitors by a transparent wall, and no actual interference occurred. Chicks were 25 subsequently tested in binary choices between a small reward after a short delay (SS) 26 and a large reward after a long delay (LL) in an isolated and constant food condition. If 27 chicks had been trained under the pseudocompetition and variable food, they chose LL 28 significantly less frequently than the other three groups. The effect disappeared when 29 the LL delay was omitted, suggesting that chicks accurately memorized the food amount. 30The food variance is thus a necessary condition for the stronger temporal discounting. 31Otherwise, the observed effect could be ascribed to a paradoxical risk proneness 32 associated with the variable option. In experiment 2, we compared four groups of chicks 33 in which food amount varied either in SS or LL, or both. The subsequent binary choice 34 tests revealed that the chicks chose SS irrespective of whether SS or LL had varied. 35These results cannot be explained in terms of a greater risk-prone choice of the variable 36 option. Coincidence of perceived competition and food variance, at least in one option, 37 is sufficient for chicks to develop choice impulsiveness. 38 39

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