Orbitofrontal cortex neurons

Reward value

Choices between 2 options (bundles) that each have 2 reward components can address the issue (top right). When each reward component is plotted on a 2D map, lines connect bundles of equal utility, as assessed by equal choice frequency (indifference) (bottom left). Transitivity confirms that higher lines represent higher utility (bottom right).

Reward signal

Preferred (higher valued) choice options elicit stronger responses in single orbitofrontal neuron, whereas equally preferred options elicit similar responses (top right). The neuronal population responses match the behavioural indifference curves within their 95% confidence interval (bottom).

The continuing consumption of a bundle containing blackcurrant juice and grape juice changes the value relationship between the two juices (left): gradually less blackcurrant juice is given up to gain the same amount of grape juice (coloured dots), as shown by progressively flattening choice indifference curves (coloured curves). Thus, grape juice has lost value relative to blackcurrant juice, indicating satiety for grape juice relative to blackcurrant juice. The neuronal responses to the bundle stimuli follow the flattened indifference curves (right), as shown by the responses with sated grape juice (bottom right). Thus, the reward signal in OFC neurons reflects satiety-induced value changes of individual choice options.

Signal in orbitofrontal cortex

A three-dimensional display of increasing scalar signal of orbitofrontal neurons with increasing preference (utility) of two-dimensional vectorial choice options (x and y: amounts of the two juices, z (x,y): neuronal signal as a function of both juice amounts).

Economic risk

Economic risk can be defined as statistical variance: larger variance indicates more risk (mean-preserving spread; Rothschild & Stiglitz 1970). Some neurons in orbitofrontal cortex signal this form of risk but do not signal reward value.

Reward Preference

Monkeys change their preference for the same reward depending on the available altervative, and neurons in the orbitofrotal do the same: when a morsel of apple is preferred to a piece of cereal, the neuron responds more to the apple than to the cereal (Block 1). When a raisin is preferred to a morsel of apple, the neuron responds more to rthe aisin and no longer to the apple (Block 2).