Traditionally the object of economic theory and experimental psychology, economic choice recently became a lively research focus in systems neuroscience. Here I summarize the emerging results and ...propose a unifying model of how economic choice might function at the neural level. Economic choice entails comparing options that vary on multiple dimensions. Hence, while choosing, individuals integrate different determinants into a subjective value; decisions are then made by comparing values. According to the good-based model, the values of different goods are computed independently of one another, which implies transitivity. Values are not learned as such, but rather computed at the time of choice. Most importantly, values are compared within the space of goods, independent of the sensorimotor contingencies of choice. Evidence from neurophysiology, imaging, and lesion studies indicates that abstract representations of value exist in the orbitofrontal and ventromedial prefrontal cortices. The computation and comparison of values may thus take place within these regions.
Remarkable progress has been made in recent years toward understanding the functions of the orbitofrontal cortex (OFC). The finding that neurons in this area encode the subjective value monkeys ...assign to different goods while making choices has been confirmed and extended by numerous studies using both primate neurophysiology and human imaging. Moreover, new lesion studies demonstrated that subjective values computed in the OFC are causally and specifically related to choice behavior. Importantly, values in the OFC are attached to goods, not to actions or to spatial locations. Furthermore, subjective values appear to be computed in this area even if the situation does not require a choice. In the light of this growing body of work, we propose that the primary function of the OFC is the computation of good identities and subjective values in an representation. In this view, OFC neurons compute the subjective value of a good whenever that good is behaviorally relevant.
Previous work showed that economic decisions can be made independently of spatial contingencies. However, when goods available for choice bear different action costs, the decision necessarily ...reflects aspects of the action. One possibility is that "stimulus values" are combined with the corresponding action costs in a motor representation, and decisions are then made in actions space. Alternatively, action costs could be integrated with other determinants of value in a non-spatial representation. If so, decisions under variable action costs could take place in goods space. Here, we recorded from orbitofrontal cortex while monkeys chose between different juices offered in variable amounts. We manipulated action costs by varying the saccade amplitude, and we dissociated in time and space offer presentation from action planning. Neurons encoding the binary choice outcome did so well before the presentation of saccade targets, indicating that decisions were made in goods space.
Economic choice behavior entails the computation and comparison of subjective values. A central contribution of neuroeconomics has been to show that subjective values are represented explicitly at ...the neuronal level. With this result at hand, the field has increasingly focused on the difficult question of where in the brain and how exactly subjective values are compared to make a decision. Here, we review a broad range of experimental and theoretical results suggesting that good-based decisions are generated in a neural circuit within the orbitofrontal cortex (OFC). The main lines of evidence supporting this proposal include the fact that goal-directed behavior is specifically disrupted by OFC lesions, the fact that different groups of neurons in this area encode the input and the output of the decision process, the fact that activity fluctuations in each of these cell groups correlate with choice variability, and the fact that these groups of neurons are computationally sufficient to generate decisions. Results from other brain regions are consistent with the idea that good-based decisions take place in OFC and indicate that value signals inform a variety of mental functions. We also contrast the present proposal with other leading models for the neural mechanisms of economic decisions. Finally, we indicate open questions and suggest possible directions for future research.
Padoa-Schioppa and Conen review recent advances on the neuronal mechanisms underlying economic choices. They propose that good-based decisions are formed in a neural circuit within the orbitofrontal cortex.
While making economic choices, individuals assign subjective values to the available options. Values computed in different behavioral conditions, however, can vary substantially. The same person ...might choose some times between goods worth a few dollars, and other times between goods worth thousands of dollars, or more. How does the brain system that computes values -- the "valuation system" -- handle this large variability? Here we show that the representation of value in the orbitofrontal cortex (OFC), an area implicated in value assignment during economic choice, adapts to the behavioral condition of choice and, more specifically, to the range of values available in any given condition. In the experiments, monkeys chose between different juices and their choice patterns provided a measure of subjective value. Value ranges were varied from session to session and, in each session, OFC neurons encoded values in a linear way. Across the population, the neuronal sensitivity (defined as the change in neuronal activity elicited by the increase in one value unit) was inversely proportional to the value range. Conversely, the neuronal activity range did not depend on the value range. This phenomenon of range adaptation complements that of menu invariance observed in a previous study. Indeed, the activity of each neuron adapts to the range values it encodes but does not depend on other available goods. Our results thus suggest that the representation of value in the OFC is at one time instantiative of preference transitivity (menu invariance) and computationally efficient (range adaptation).
The role of the dorsal anterior cingulate cortex (ACCd) in decision making has often been discussed but remains somewhat unclear. On the one hand, numerous studies implicated this area in decisions ...driven by effort or action cost. On the other hand, work on economic choices between goods (under fixed action costs) found that neurons in ACCd encoded only post-decision variables. To advance our understanding of the role played by this area in decision making, we trained monkeys to choose between different goods (juice types) offered in variable amounts and with different action costs. Importantly, the task design dissociated computation of the action cost from planning of any particular action. Neurons in ACCd encoded the chosen value and the binary choice outcome in several reference frames (chosen juice, chosen cost, chosen action). Thus, this area provided a rich representation of post-decision variables. In contrast to the OFC, neurons in ACCd did not represent pre-decision variables such as individual offer values in any reference frame. Hence, ongoing decisions are unlikely guided by ACCd. Conversely, neuronal activity in this area might inform subsequent actions.
We examined the activity of individual cells in the primate anterior cingulate cortex during an economic choice task. In the experiments, monkeys chose between different juices offered in variables ...amounts and subjective values were inferred from the animals' choices. We analyzed neuronal firing rates in relation to a large number of behaviorally relevant variables. We report three main results. First, there were robust differences between the dorsal bank (ACCd) and the ventral bank (ACCv) of the cingulate sulcus. Specifically, neurons in ACCd but not in ACCv were modulated by the movement direction. Furthermore, neurons in ACCd were most active before movement initiation, whereas neurons in ACCv were most active after juice delivery. Second, neurons in both areas encoded the identity and the subjective value of the juice chosen by the animal. In contrast, neither region encoded the value of individual offers. Third, the population of value-encoding neurons in both ACCd and ACCv underwent range adaptation. With respect to economic choice, it is interesting to compare these areas with the orbitofrontal cortex (OFC), previously examined. While neurons in OFC encoded both pre-decision and post-decision variables, neurons in ACCd and ACCv only encoded post-decision variables. Moreover, the encoding of the choice outcome (chosen value and chosen juice) in ACCd and ACCv trailed that found in OFC. These observations indicate that economic decisions (i.e., value comparisons) take place upstream of ACCd and ACCv. The coexistence of choice outcome and movement signals in ACCd suggests that this area constitutes a gateway through which the choice system informs motor systems.
Previous work indicates that economic decisions can be made independently of the visuomotor contingencies of the choice task (space of goods). However, the neuronal mechanisms through which the ...choice outcome (the chosen good) is transformed into a suitable action plan remain poorly understood. Here we show that neurons in lateral prefrontal cortex reflect the early stages of this good-to-action transformation. Monkeys chose between different juices. The experimental design dissociated in space and time the presentation of the offers and the saccade targets associated with them. We recorded from the orbital, ventrolateral, and dorsolateral prefrontal cortices (OFC, LPFCv, and LPFCd, respectively). Prior to target presentation, neurons in both LPFCv and LPFCd encoded the choice outcome in goods space. After target presentation, they gradually came to encode the location of the targets and the upcoming action plan. Consistent with the anatomical connectivity, all spatial and action-related signals emerged in LPFCv before LPFCd.
•Economic choices can be made independent of action selection (goods space)•Good-based decisions imply a transformation from goods space to action space•Neurons in lateral prefrontal cortex (LPFC) reflect the good-to-action transformation•Information flows from orbitofrontal cortex, to ventral LPFV, to dorsal LPFC
Good-based economic decisions take place in an abstract, action-independent neuronal representation. The choice outcome, computed in goods space, is then transformed into a suitable action plan. Cai and Padoa-Schioppa show that neurons in the lateral prefrontal cortex reflect this good-to-action transformation.
: Economic choice is the behavior observed when individuals select one of many available options solely based on subjective preferences. Behavioral evidence suggests that economic choice entails two ...mental processes: values are first assigned to the available options, and a decision is subsequently made between these values. Numerous reports show that lesions to the orbitofrontal cortex (OFC) lead to choice deficits in various domains, and imaging studies indicate that the OFC activates when people make choices. In this chapter, we review evidence from single cell recordings linking the OFC more specifically to valuation. Individual neurons in the OFC encode the value that monkeys assign to different beverages when they choose between them. These neurons encode economic value as a subjective quantity. Most importantly, neurons in the OFC encode economic value per se, not as a modulation of sensory or motor processes. This trait distinguishes the value representation in the OFC from that observed in other brain areas. That OFC neurons encode economic value independently of visuomotor contingencies suggests that economic choice is fundamentally a choice between goods (good‐based model) rather than a choice between actions (action‐based model).
Multiple lines of evidence link economic choices to the orbitofrontal cortex (OFC), but other brain regions may contribute to the computation and comparison of economic values. A particularly strong ...candidate is the basolateral amygdala (BLA). Amygdala lesions impair performance in reinforcer devaluation tasks, suggesting that the BLA contributes to value computation. Furthermore, previous studies of the BLA have found neuronal activity consistent with a value representation. Here, we recorded from the BLA of two male rhesus macaques choosing between different juices. Offered quantities varied from trial to trial, and relative values were inferred from choices. Approximately one-third of BLA cells were task-related. Our analyses revealed the presence of three groups of neurons encoding variables
,
, and
In this respect, the BLA appeared similar to the OFC. The two areas differed for the proportion of neurons in each group, as the fraction of
cells was significantly higher in the BLA. Importantly, the activity of these neurons reflected the subjective nature of value. Firing rates in the BLA were sustained throughout the trial and maximal after juice delivery. In contrast, firing rates in the OFC were phasic and maximal shortly after offer presentation. Our results suggest that the BLA supports economic choice and reward expectation.
Economic choices rely on the orbitofrontal cortex (OFC), but other brain regions may contribute to this behavior. A strong candidate is the basolateral amygdala (BLA). Previous results are consistent with a neuronal representation of value, but the role of the BLA in economic decisions remains unclear. Here, we recorded from monkeys choosing between juices. Neurons in the BLA encoded three decision variables:
,
, and
These variables were also identified in the OFC. The two areas differed in the proportion of cells encoding each variable and in the activation timing. In the OFC, firing rates peaked shortly after offer presentation; in the BLA, firing rates were sustained and peaked after juice delivery. These results suggest that the BLA supports choices and reward expectation.
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