Neural correlates of the proximity and quantity of anticipated food rewards in the ventral striatum of domestic chicks

Striatal and Tegmental Neurons Code Critical Signals for Temporal-Difference Learning of State Value in Domestic Chicks

To ensure survival, animals must update the internal representations of their environment in a trial-and-error fashion. Psychological studies of associative learning and neurophysiological analyses of dopaminergic neurons have suggested that this updating process involves the temporal-difference (TD) method in the basal ganglia network. However, the way in which the component variables of the TD method are implemented at the neuronal level is unclear. To investigate the underlying neural mechanisms, we trained domestic chicks to associate color cues with food rewards. We recorded neuronal activities from the medial striatum or tegmentum in a freely behaving condition and examined how reward omission changed neuronal firing. To compare neuronal activities with the signals assumed in the TD method, we simulated the behavioral task in the form of a finite sequence composed of discrete steps of time. The three signals assumed in the simulated task were the prediction signal, the target signal for updating, and the TD-error signal. In both the medial striatum and tegmentum, the majority of recorded neurons were categorized into three types according to their fitness for three models, though these neurons tended to form a continuum spectrum without distinct differences in the firing rate. Specifically, two types of striatal neurons successfully mimicked the target signal and the prediction signal. A linear summation of these two types of striatum neurons was a good fit for the activity of one type of tegmental neurons mimicking the TD-error signal. The present study thus demonstrates that the striatum and tegmentum can convey the signals critically required for the TD method. Based on the theoretical and neurophysiological studies, together with tract-tracing data, we propose a novel model to explain how the convergence of signals represented in the striatum could lead to the computation of TD error in tegmental dopaminergic neurons.

Neurons in the pigeon caudolateral nidopallium differentiate Pavlovian conditioned stimuli but not their associated reward value in a sign-tracking paradigm

Animals exploit visual information to identify objects, form stimulus-reward associations, and prepare appropriate behavioral responses. The nidopallium caudolaterale (NCL), an associative region of the avian endbrain, contains neurons exhibiting prominent response modulation during presentation of reward-predicting visual stimuli, but it is unclear whether neural activity represents valuation signals, stimulus properties, or sensorimotor contingencies. To test the hypothesis that NCL neurons represent stimulus value, we subjected pigeons to a Pavlovian sign-tracking paradigm in which visual cues predicted rewards differing in magnitude (large vs. small) and delay to presentation (short vs. long). Subjects' strength of conditioned responding to visual cues reliably differentiated between predicted reward types and thus indexed valuation. The majority of NCL neurons discriminated between visual cues, with discriminability peaking shortly after stimulus onset and being maintained at lower levels throughout the stimulus presentation period. However, while some cells' firing rates correlated with reward value, such neurons were not more frequent than expected by chance. Instead, neurons formed discernible clusters which differed in their preferred visual cue. We propose that this activity pattern constitutes a prerequisite for using visual information in more complex situations e.g. requiring value-based choices.

Anticipatory and foraging behaviors in response to palatable food reward in chickens: effects of dopamine D2 receptor blockade and domestication

Behaviors associated with anticipation and search for palatable food may provide information about dopaminergic reward processes and positive motivational affect in animals. The overall aim was to investigate the involvement of dopamine signaling in the regulation of cue-induced anticipation and search for palatable food reward in chicken, and whether domestication has affected expression of reward-related behaviors. The specific aims were to describe effects of mealworms (palatable food for hens) and haloperidol (a dopamine D2 antagonist) on foraging behaviors and cue-induced anticipatory behaviors in Red Junglefowl (RJF; the wild ancestor of modern laying hens) and a white layer hybrid (LSL). RJF (n=26) and LSL (n=20) were initially trained on a conditioning schedule to anticipate mealworms (unconditioned stimulus; US) 25s after exposure to a red light (conditioned stimulus; CS). For the experiment, hens received haloperidol or saline injections 30 min before exposure to one CS+US combination. Behavior was registered 10 min before CS and 10 min after US (foraging behaviors), and during the CS-US interval (anticipatory behaviors). Higher frequencies of CS-induced anticipatory head movements, faster approach to rewards, and higher frequency of foraging behaviors were found in LSL compared to RJF. Haloperidol suppressed CS-induced head movements in both breeds, and the frequency of foraging behaviors after reward delivery. The results support a role of dopamine signaling in the regulation of reward processes in chickens, and suggest that domestication has changed the threshold for perceiving food incentives and/or for expressing reward-related behaviors that may be indicative of positive motivational affect in hens.

Competitor suppresses neuronal representation of food reward in the nucleus accumbens/medial striatum of domestic chicks

To investigate the role of social contexts in controlling the neuronal representation of food reward, we recorded single neuron activity in the medial striatum/nucleus accumbens of domestic chicks and examined whether activities differed between two blocks with different contexts. Chicks were trained in an operant task to associate light-emitting diode color cues with three trial types that differed in the type of food reward: no reward (S-), a small reward/short-delay option (SS), and a large reward/long-delay alternative (LL). Amount and duration of reward were set such that both of SS and LL were chosen roughly equally. Neurons showing distinct cue-period activity in rewarding trials (SS and LL) were identified during an isolation block, and activity patterns were compared with those recorded from the same neuron during a subsequent pseudo-competition block in which another chick was allowed to forage in the same area, but was separated by a transparent window. In some neurons, cue-period activity was lower in the pseudo-competition block, and the difference was not ascribed to the number of repeated trials. Comparison at neuronal population level revealed statistically significant suppression in the pseudo-competition block in both SS and LL trials, suggesting that perceived competition generally suppressed the representation of cue-associated food reward. The delay- and reward-period activities, however, did not significantly different between blocks. These results demonstrate that visual perception of a competitive forager per se weakens the neuronal representation of predicted food reward. Possible functional links to impulse control are discussed.

Food rewards modulate the activity of song neurons in Bengalese finches

Vocal learning, a critical component of speech acquisition, is a rare trait in animals. Songbirds are a well-established animal model in vocal learning research; male birds acquire novel vocal patterns and have a well-developed 'song system' in the brain. Although this system is unique to songbirds, anatomical and physiological studies have reported similarities between the song system and the thalamo-cortico-basal ganglia circuit that is conserved among reptiles, birds, and mammals. Here, we focused on the similarity of the neural response between these two systems while animals were engaging in operant tasks. Neurons in the basal ganglia of vertebrates are activated in response to food rewards and reward predictions in behavioral tasks. A striatal nucleus in the avian song system, Area X, is necessary for vocal learning and is considered specialized for singing. We found that the spiking activity of singing-related Area X neurons was modulated by food rewards and reward signals in an operant task. As previous studies showed that Area X is not critical for general cognitive tasks, the role of Area X in general learning might be limited and vestigial. However, our results provide a new viewpoint to investigate the independence of the vocal learning system from neural systems involved in other cognitive tasks.

Towards autonomous neuroprosthetic control using Hebbian reinforcement learning

OBJECTIVE

Our goal was to design an adaptive neuroprosthetic controller that could learn the mapping from neural states to prosthetic actions and automatically adjust adaptation using only a binary evaluative feedback as a measure of desirability/undesirability of performance.

APPROACH

Hebbian reinforcement learning (HRL) in a connectionist network was used for the design of the adaptive controller. The method combines the efficiency of supervised learning with the generality of reinforcement learning. The convergence properties of this approach were studied using both closed-loop control simulations and open-loop simulations that used primate neural data from robot-assisted reaching tasks.

MAIN RESULTS

The HRL controller was able to perform classification and regression tasks using its episodic and sequential learning modes, respectively. In our experiments, the HRL controller quickly achieved convergence to an effective control policy, followed by robust performance. The controller also automatically stopped adapting the parameters after converging to a satisfactory control policy. Additionally, when the input neural vector was reorganized, the controller resumed adaptation to maintain performance.

SIGNIFICANCE

By estimating an evaluative feedback directly from the user, the HRL control algorithm may provide an efficient method for autonomous adaptation of neuroprosthetic systems. This method may enable the user to teach the controller the desired behavior using only a simple feedback signal.

Visual object categorization in birds and primates: integrating behavioral, neurobiological, and computational evidence within a "general process" framework

Previous comparative work has suggested that the mechanisms of object categorization differ importantly for birds and primates. However, behavioral and neurobiological differences do not preclude the possibility that at least some of those mechanisms are shared across these evolutionarily distant groups. The present study integrates behavioral, neurobiological, and computational evidence concerning the "general processes" that are involved in object recognition in vertebrates. We start by reviewing work implicating error-driven learning in object categorization by birds and primates, and also consider neurobiological evidence suggesting that the basal ganglia might implement this process. We then turn to work with a computational model showing that principles of visual processing discovered in the primate brain can account for key behavioral findings in object recognition by pigeons, including cases in which pigeons' behavior differs from that of people. These results provide a proof of concept that the basic principles of visual shape processing are similar across distantly related vertebrate species, thereby offering important insights into the evolution of visual cognition.

Instantaneous and cumulative influences of competition on impulsive choices in domestic chicks

This study examined instantaneous and cumulative effects of competitive interactions on impulsiveness in the inter-temporal choices in domestic chicks. Chicks were trained to peck colored beads to gain delayed food rewards (1 or 6 grains of millet delivered after a delay ranging between 0 and 4.5 s), and were tested in binary choices between a small–short delay option (SS) and a large–long delay alternative (LL). To examine whether competitive foraging instantaneously changes impulsiveness, we intraindividually compared choices between two consecutive tests in different contexts, one with competitors and another without. We found that (1) the number of the choice of LL was not influenced by competition in the tests, but (2) the operant peck latency was shortened by competition, suggesting a socially enhanced incentive for food. To further examine the lasting changes, two groups of chicks were consecutively trained and tested daily for 2 weeks according to a “behavioral titration” procedure, one with competitors and another without. Inter-group comparisons of the choices revealed that (3) choice impulsiveness gradually decreased along development, while (4) the chicks trained in competition maintained a higher level of impulsiveness. These results suggest that competitive foraging causes impulsive choices not by direct/contextual modification. Causal link between the instantaneous enhancement of incentive and the gradual effects on impulsiveness remains to be examined. Some (yet unspecified) factors may be indirectly involved.

Why we should use animals to study economic decision making - a perspective

Despite the rich tradition in psychology and biology, animals as research subjects have never gained a similar acceptance in microeconomics research. With this article, we counter this trend of negligence and try to convey the message that animal models are an indispensible complement to the literature on human economic decision making. This perspective review departs from a description of the similarities in economic and evolutionary theories of human and animal decision making, with particular emphasis on the optimality aspect that both classes of theories have in common. In a second part, we outline that actual, empirically observed decisions often do not conform to the normative ideals of economic and ecological models, and that many of the behavioral violations found in humans can also be found in animals. In a third part, we make a case that the sense or nonsense of the behavioral violations of optimality principles in humans can best be understood from an evolutionary perspective, thus requiring animal research. Finally, we conclude with a critical discussion of the parallels and inherent differences in human and animal research.

Heterogeneous coding of temporally discounted values in the dorsal and ventral striatum during intertemporal choice

In choosing between different rewards expected after unequal delays, humans and animals often prefer the smaller but more immediate reward, indicating that the subjective value or utility of reward is depreciated according to its delay. Here, we show that neurons in the primate caudate nucleus and ventral striatum modulate their activity according to temporally discounted values of rewards with a similar time course. However, neurons in the caudate nucleus encoded the difference in the temporally discounted values of the two alternative targets more reliably than neurons in the ventral striatum. In contrast, neurons in the ventral striatum largely encoded the sum of the temporally discounted values, and therefore, the overall goodness of available options. These results suggest a more pivotal role for the dorsal striatum in action selection during intertemporal choice.

Reward-associated gamma oscillations in ventral striatum are regionally differentiated and modulate local firing activity

Oscillations of local field potentials (LFPs) in the gamma range are found in many brain regions and are supposed to support the temporal organization of cognitive, perceptual, and motor functions. Even though gamma oscillations have also been observed in ventral striatum, one of the brain's most important structures for motivated behavior and reward processing, their specific function during ongoing behavior is unknown. Using a movable tetrode array, we recorded LFPs and activity of neural ensembles in the ventral striatum of rats performing a reward-collection task. Rats were running along a triangle track and in each round collected one of three different types of rewards. The gamma power of LFPs on subsets of tetrodes was modulated by reward-site visits, discriminated between reward types, between baitedness of reward locations and was different before versus after arrival at a reward site. Many single units in ventral striatum phase-locked their discharge pattern to the gamma oscillations of the LFPs. Phase-locking occurred more often in reward-related than in reward-unrelated neurons and LFPs. A substantial number of simultaneously recorded LFPs correlated poorly with each other in terms of gamma rhythmicity, indicating that the expression of gamma activity was heterogeneous and regionally differentiated. The orchestration of LFPs and single-unit activity by way of gamma rhythmicity sheds light on the functional architecture of the ventral striatum and the temporal coordination of ventral striatal activity for modulating downstream areas and regulating synaptic plasticity.

How do African grey parrots (Psittacus erithacus) perform on a delay of gratification task?

Humans and other animals often find it difficult to choose a delayed reward over an immediate one, even when the delay leads to increased pay-offs. Using a visible incremental reward procedure, we tested the ability of three grey parrots to maintain delay of gratification for an increasingly valuable food pay-off. Up to five sunflower seeds were placed within the parrot's reach, one at a time, at a rate of one seed per second. When the parrot took a seed the trial was ended and the birds consumed the accumulated seeds. Parrots were first tested in daily sessions of ten trials and then with single daily trials. For multiple trial sessions, all three parrots showed some limited improvement across 30 sessions. For single trial sessions, only one parrot showed any increase in seed acquisition across trials. This parrot was also able to consistently obtain two or more seeds per trial (across both multiple and single trial conditions) but was unable to able to wait 5 s to obtain the maximum number of seeds. This parrot was also tested on a slower rate of seed presentation, and this significantly reduced her mean seed acquisition in both multiple and single trial conditions, suggesting that both value of reward available and delay duration impact upon self-control. Further manipulation of both the visibility and proximity of seeds during delay maintenance had little impact upon tolerance of delays for both parrots tested in this condition. This task demanded not just a choice of delayed reward but the maintenance of delayed gratification and was clearly difficult for the parrots to learn; additional training or alternative paradigms are required to better understand the capacity for self-control in this and other species.

Effort-based cost-benefit valuation and the human brain

In both the wild and the laboratory, animals' preferences for one course of action over another reflect not just reward expectations but also the cost in terms of effort that must be invested in pursuing the course of action. The ventral striatum and dorsal anterior cingulate cortex (ACCd) are implicated in the making of cost-benefit decisions in the rat, but there is little information about how effort costs are processed and influence calculations of expected net value in other mammals including humans. We performed a functional magnetic resonance imaging study to determine whether and where activity in the human brain was available to guide effort-based cost-benefit valuation. Subjects were scanned while they performed a series of effortful actions to obtain secondary reinforcers. At the beginning of each trial, subjects were presented with one of eight different visual cues that they had learned indicated how much effort the course of action would entail and how much reward could be expected at its completion. Cue-locked activity in the ventral striatum and midbrain reflected the net value of the course of action, signaling the expected amount of reward discounted by the amount of effort to be invested. Activity in ACCd also reflected the interaction of both expected reward and effort costs. Posterior orbitofrontal and insular activity, however, only reflected the expected reward magnitude. The ventral striatum and anterior cingulate cortex may be the substrate of effort-based cost-benefit valuation in primates as well as in rats.

Non-visually evoked activity of isthmo-optic neurons in awake, head-unrestrained quail

Changes in the internal state of the brain may modulate retinal function. In birds, most neurons in the isthmo-optic (IO) nucleus project their axons topographically into the contralateral retina, and activity in IO neurons enhances visual responses of retinal ganglion cells in the target retinal region. To elucidate the significance of this pathway, we recorded spikes of IO neurons in four awake Japanese quail using an implanted electrode assembly while recording unrestrained head movements. The IO neurons fired passively in response to visual stimuli in receptive fields and non-visually without visual stimuli or eye-head movements. Non-visually evoked activity was observed in the middle of eye-head fixation, as well as at about 200 ms before the onset of head saccades. Intensity of activity before onset of head saccades depended on the direction of motion of subsequent head saccades. Local retinal output may be enhanced by centrifugal signals before gaze shifts.

Sustained activation and executive control in the avian prefrontal cortex

We review our studies examining neural correlates of directed forgetting and executive control in the avian prefrontal cortex. One of the fundamental forms of executive control is the ability to selectively filter information, retaining that which is critical for the current purposes and discarding that which is not. In our first experiment, we trained birds on a directed-forgetting version of a delayed matching-to-sample task. Following a sample stimulus, a bird heard either a remember tone indicating that a memory test would follow, or a forget tone indicating that no memory test would be given. We found that neural activity in the avian prefrontal cortex increased when the bird was told to remember, and decreased when the bird was told to forget. Behavioral probe tests confirmed that the animals were forgetting on forget trials. Although the sustained activation observed on remember trials and the absence of such activation on forget trials could be a code of remembering and forgetting the sample stimulus, it could also be a code of the possibility of obtaining a reward. To address this issue we conducted a second study in which we used three cues: remember, forget, and forget-reward. The forget-reward cue instructed the subject to forget the sample yet at the same time provided a free reward. Neural activity on forget-reward trials matched that on remember trials tentatively indicating that the sustained activation on remember trials might be a reward code rather than a sample stimulus code. Behavioral probe tests, however, failed to indicate that the animals were forgetting on forget-reward trials, and hence it still is possible that the sustained activation could be a code for memory of the sample stimulus.

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

Studies on the foraging choices are reviewed, with an emphasis on the neural representations of elementary factors of food (i.e., amount, delay and consumption time) in the avian brain. Domestic chicks serve as an ideal animal model in this respect, as they quickly associate cue colors with subsequently supplied food rewards, and their choices are quantitatively linked with the rewards. When a pair of such color cues was simultaneously presented, the trained chicks reliably made choices according to the profitability of food associated with each color. Two forebrain regions are involved in distinct aspects of choices; i.e., nucleus accumbens-medial striatum (Ac-MSt) and arcopallium intermedium (AI), an association area in the lateral forebrain. Localized lesions of Ac-MSt enhanced delay aversion, and the ablated chicks made impulsive choices of immediate reward more frequently than sham controls. On the other hand, lesions of AI enhanced consumption-time aversion, and the ablated chicks shifted their choices toward easily consumable reward with their impulsiveness unchanged; delay and consumption time are thus doubly dissociated. Furthermore, chicks showed distinct patterns of risk-sensitive choices depending on the factor that varied at trials. Risk aversion occurred when food amount varied, whereas consistent risk sensitivity was not found when the delay varied; amount and delay were not interchangeable. Choices are thus deviated from those predicted as optima. Instead, factors such as amount, delay and consumption time could be separately represented and processed to yield economically sub-optimal choices.

Localized lesions of arcopallium intermedium of the lateral forebrain caused a handling-cost aversion in the domestic chick performing a binary choice task

Behavioral effects of handling cost (time and/or energetic cost for food consumption) on choice were examined using domestic chicks trained in operant task reinforced by delayed food rewards. When scattered sesame was delivered in more demanding conditions, a colored cue bead associated with six grains ('large' and 'costly' reward) was chosen progressively less frequently against another bead associated with one grain ('small' and 'not costly' reward). The choice thus proved to be highly sensitive to the anticipated handling cost. Excitotoxic lesion of the bilateral arcopallium intermedium also selectively reduced the choice of the six grains, while leaving actual cost investment (number of pecks and handling time) unaltered. No significant changes occurred in choices between one grain of sesame ('small' and 'not costly' reward) and one grain of barley (or a ball composed of six sesame grains glued by starch; 'large' and 'not costly' reward), indicating that choice based on anticipated food amount was not impaired. On the other hand, lesion of the ventral striatum did not change the choice ratio in any trial types. Operant peck latencies somewhat depended on food rewards, but were not affected by lesions of the arcopallium or the ventral striatum. The arcopallium could contribute to foraging behaviors by enabling chicks to overcome the handling cost, thus gaining more beneficial food. Furthermore, the present results indicate doubly dissociated functional roles of the ventral striatum and the arcopallium, the former in the cost of traveling for food and the latter in the cost of handling food, respectively.

Single forebrain neurons represent interval timing and reward amount during response scheduling

Climbing activity, the gradual increase of neural discharge rate across a delay, has been suggested to play a crucial role in interval timing. However, most previous studies demonstrated climbing activity only in conjunction with tasks that involved a passive tracking of the passage of time, but that did not necessitate to actively time an event, e.g. a motor response. To demonstrate the significance of climbing activity for action timing, we trained pigeons in a self-control task requiring either immediate responding to a key after the onset of a light cue ('rapid-response' trials), or waiting for a fixed interval after cue presentation before responding to the key ('wait' trials). The cue also indicated whether a correctly timed response would be rewarded with a large or a small reward. Single-cell recordings in the Nidopallium caudolaterale, the avian prefrontal cortex, revealed that some neurons showed climbing activity between cue onset and response. Their increase in firing rate was flatter and reached the peak later in wait compared with rapid-response trials. An error analysis confirmed that, relative to correct responses, premature responses were accompanied by steeper, and tardy responses by flatter ramps. In addition, the climbing discharge pattern was modulated by the amount of the anticipated reward, suggesting that timing is an intrinsic property of neurons encoding other task-related information. These results demonstrate the behavioural and motivational significance of climbing activity in prospective information encoding. Our study supports a recent paradigm shift in our understanding of the vertebrate brain evolution, and it provides further evidence for the similarity between the mammalian cortex and the avian pallium.

Nucleus accumbens subregions: hodological and immunohistochemical study in the domestic chick (Gallus domesticus)

The nucleus accumbens was identified in avian species some time ago. However, the precise localization and extent of this nucleus is still a matter of controversy. We have used immunolabeling against calbindin, neuropeptide Y, and DARPP-32 (dopamine- and adenosine-related phosphoprotein, 32 kDa) for the selective marking of putative accumbens subdivisions and have followed the anterograde transport of biotinylated dextran amine injected to the nucleus tractus solitarii region of 7-day-old domestic chicks. The nucleus accumbens extending between rostrocaudal atlas coordinates A 10.6 and A 8.8 can be subdivided into the core and shell, the core corresponding to the ventromedial and juxtaventricular medial striatum laterodorsal to the bed nucleus of stria terminalis, and the shell representing an arched region situated ventrally and ventrolaterally to the core. Immunoreactivity to both calbindin and neuropeptide Y is more intense in the shell than in the core division. DARPP-32 immunolabeling does not differ in the two divisions but is markedly weaker in the bed nucleus of stria terminalis, enabling the separation of this nucleus from the surrounding accumbens subdivisions. Fibers from the nucleus solitarius predominantly terminate in the shell division, similar to the situation described in mammals. Whereas the suggested core lies entirely within the boundary of the medial striatum, the shell seems partially to overlap the ventral pallidum. We have been unable to subdivide the remaining part of accumbens lying rostral to A 10.6 into a putative shell and core by the methods employed in the present study. This region probably corresponds to the rostral pole of the nucleus accumbens.

Neural systems implicated in delayed and probabilistic reinforcement

This review considers the theoretical problems facing agents that must learn and choose on the basis of reward or reinforcement that is uncertain or delayed, in implicit or procedural (stimulus-response) representational systems and in explicit or declarative (action-outcome-value) representational systems. Individual differences in sensitivity to delays and uncertainty may contribute to impulsivity and risk taking. Learning and choice with delayed and uncertain reinforcement are related but in some cases dissociable processes. The contributions to delay and uncertainty discounting of neuromodulators including serotonin, dopamine, and noradrenaline, and of specific neural structures including the nucleus accumbens core, nucleus accumbens shell, orbitofrontal cortex, basolateral amygdala, anterior cingulate cortex, medial prefrontal (prelimbic/infralimbic) cortex, insula, subthalamic nucleus, and hippocampus are examined.

Localized lesions of ventral striatum, but not arcopallium, enhanced impulsiveness in choices based on anticipated spatial proximity of food rewards in domestic chicks

The effects of bilateral chemical lesions of the ventral striatum (nucleus accumbens and the surrounding areas in the medial striatum) and arcopallium (major descending area of the avian telencephalon) were examined in 1-2-weeks old domestic chicks. Using a Y-maze, we analyzed the lesion effects on the choices that subject chicks made in two tasks with identical economical consequences, i.e., a small-and-close food reward vs. a large-and-distant food reward. In task 1, red, yellow, and green beads were associated with a feeder placed at various distances from the chicks; chicks thus anticipated the spatial proximity of food by the bead's color, whereas the quantity of the food was fixed. In task 2, red and yellow flags on the feeders were associated with various amount of food; the chicks thus anticipated the quantity of food by the flag's color, whereas the proximity of the reward could be directly visually determined. In task 1, bilateral lesions of the ventral striatum (but not the arcopallium) enhanced the impulsiveness of the chicks' choices, suggesting that choices based on the anticipated proximity were selectively changed. In task 2, similar lesions of the ventral striatum did not change choices. In both experiments, motor functions of the chicks remained unchanged, suggesting that the lesions did not affect the foraging efficiency, i.e., objective values of food. Neural correlates of anticipated food rewards in the ventral striatum (but not those in the arcopallium) could allow chicks to invest appropriate amount of work-cost in approaching distant food resources.