Neurons in the orbitofrontal cortex encode economic value

Abstract

In the study of animal behaviour, an ‘economic choice’ involves an individual animal's selection between many options based on a subjective estimation of the benefits. It has long been known that neurons in different parts of the brain respond to separate attributes, such as quantity, colour and taste. And now part of the brain, the orbitofrontal cortex (OFC) has been linked to the value judgements involved in economic choice. This was established in tests on macaque monkeys choosing whether to drink water or various types of juice. Neurons in the OFC changed their firing rate in a way that reflected the monkey's valuation of the drink. In humans, lesions in the orbitofrontal cortex are known to result in eating disorders, compulsive gambling and other conditions involving ‘choice deficit’; there is also a link to drug abuse, arguably another aspect of choice. Economic choice is the behaviour observed when individuals select one among many available options. There is no intrinsically ‘correct’ answer: economic choice depends on subjective preferences. This behaviour is traditionally the object of economic analysis1 and is also of primary interest in psychology2. However, the underlying mental processes and neuronal mechanisms are not well understood. Theories of human and animal choice1,2,3 have a cornerstone in the concept of ‘value’. Consider, for example, a monkey offered one raisin versus one piece of apple: behavioural evidence suggests that the animal chooses by assigning values to the two options4. But where and how values are represented in the brain is unclear. Here we show that, during economic choice, neurons in the orbitofrontal cortex5,6,7,8,9,10,11,12,13,14,15,16,17,18 (OFC) encode the value of offered and chosen goods. Notably, OFC neurons encode value independently of visuospatial factors and motor responses. If a monkey chooses between A and B, neurons in the OFC encode the value of the two goods independently of whether A is presented on the right and B on the left, or vice versa. This trait distinguishes the OFC from other brain areas in which value modulates activity related to sensory or motor processes19,20,21,22,23,24,25. Our results have broad implications for possible psychological models, suggesting that economic choice is essentially choice between goods rather than choice between actions. In this framework, neurons in the OFC seem to be a good candidate network for value assignment underlying economic choice.