Localized Lesion of Caudal Part of Lobus Parolfactorius Caused Impulsive Choice in the Domestic Chick: Evolutionarily Conserved Function of Ventral Striatum

Abstract

Effects of bilateral chemical lesions of the medial basal ganglia [lobus parolfactorius (LPO)] were examined in 7- to 14-d-old domestic chicks. Chicks were trained in a color discrimination task, in which the subject had to peck one of the two colored beads associated with rewards that differed in quantity (amount of food) and/or temporal proximity (delay of food delivery from peck). In experiment 1, food was given without delay, and chicks successfully learned to choose a colored bead that was associated with a larger reward than the other. In experiment 2, a colored bead (red) was associated with a large reward delivered after a delay (D = 1, 2, or 3 sec), whereas another (yellow) was associated with a small reward delivered immediately. In intact and sham-operated conditions, chicks with a longer D chose the red bead progressively fewer times. Selective lesions to the caudal LPO (but not the rostral LPO) caused impulsive choice, and the ablated chicks chose the yellow bead and gained a small-immediate reward regardless of D. However, when retrained in a null-delay condition (D = 0 sec), the lesioned chick chose the red bead again. Ability to associate novel colors with reward was also unimpaired. These results suggest that the LPO may be responsible for the anticipation of reward proximity and involved in a suppression of impulsiveness by which animals seek immediate gains. The present results also indicate a striking similarity in functional roles between the avian LPO and the nucleus accumbens/ventral striatum in mammals.

Subjective value of risky foods for individual domestic chicks: a hierarchical Bayesian model

“…By adjusting the delay of LL, an equilibrium point was found at which both SS and LL were equally chosen (Izawa et al 2003, Aoki et al 2006, in a manner compatible with the idea that chicks evaluate food by its profitability (Matsushima et al 2008). However, risk-averse choices found in this study (group 1 but not group 2 in experiment 2) suggest that subjective value is not a linear function of amount but concave as in equation (2).…”

Neuro-economics in chicks: Foraging choices based on amount, delay and cost

“…However, the actual number of pecks per pellets (i.e., experimentally measured κ) remained unchanged, indicating that the consumption cost investment did not increase. The lesions caused no effects in those choices based solely on the amount of food [4], as in the case of Ac-MSt lesions [3,24]. Furthermore, in a Y-maze task for choices between a small-immediate and a large-distant alternative [4], the lesion had no effects on the impulsiveness.…”

“…Chicks with localized lesions to Ac-MSt revealed highly enhanced impulsiveness in their choice selectively between a small-immediate reward and a large-delayed alternative [24]. The effect was evident particularly when the delay associated with the large reward (6-pellet food) was set at 1~2 seconds.…”

“…In training trials, pecking at a green bead was followed by a reward of 1 pellet delivered immediately (Fig.2); pecking at a red bead was followed by a reward of 6 pellets delivered after a delay (D), ranging between 0 to 3 sec as experimental variable [24]. A blue bead was not rewarded, irrespective of whether the chick actually pecked at the bead or not.…”

“…It is reasonable to assume that the chick Ac covers a somehow larger area than that delineated in the chick brain atlas [29]. The area named as accumbens nucleus (Acb) in the most recent atlas [35] corresponds to the "rostral LPO," which is a functionally distinct region since its lesion had no effects on impulsiveness [24]. In mammals, comparable effects were found also after lesions localized to the nucleus accumbens core [8]; it is thus reasonable to suggest that the Ac defined by Bálint and Csillag [6] corresponds better to the mammalian counterpart, rather than the Acb outlined in the atlas by Puelles et al [35].…”