emotion, scientific aspects Emotions are subjective states produced by rewards and punishments. Rewards are things for which an animal (including humans) will work, and punishments (technically called ‘punishers’) are stimuli that an animal will work to escape from or avoid. Rewards and punishers are called ‘reinforcers’ because they strengthen the probability of certain sorts of behaviour. Some emotion-producing stimuli (such as the taste of food to a hungry animal, or pain) are unlearned or ‘primary’ reinforcers. Other, initially neutral stimuli produce emotions because they have been associated with such primary reinforcers, thereby becoming ‘secondary’ reinforcers. For example, you may experience the emotional state of fear if you hear the voice (the conditioned stimulus) of someone who has previously caused you pain (a primary reinforcer).

The wide variety of different emotions that we feel depend not only on whether the stimulus is rewarding or punishing, and how strong it is, but also on present and past associations surrounding the experience. Even the type of response that is possible can alter the emotional state. Denial of an expected reward, which might normally produce an outburst of anger, will trigger only silent sadness or grief, if the situation forbids an active response.

The functions of emotion

Emotions seem irrational and maladaptive, occupying the body and the mind with apparently irrelevant thoughts and actions. However, they can result in a variety of adaptive functions:1. Emotions can trigger useful responses of the autonomic nervous system (e.g. a change in heart rate) and the release of hormones, such as adrenaline, which prepare the body for action.2. Emotions act as a simple and flexible ‘interface’ between sensory inputs and motor outputs. The kinds of stimuli that act as primary (unlearned) rewards and punishers may somehow be directly specified in our brains by genetic information, and these stimuli define ‘goals’ for actions. For example, genes may specify that strong stimulation of the skin or deep tissues produces a state of pain, which animals (including humans) are built to avoid or escape. The state produced by the painful stimulus is an emotional state, which has the adaptive function of identifying and maintaining the goal for an action. This is an efficient design, for the genes involved need only specify the goals, and not the actions themselves, so that the actions can be selected flexibly to meet the goals.3. Emotion is motivating. For example, fear provides the motivation for actions performed to avoid painful stimuli.4. Emotions may aid communication, as emphasized by Charles Darwin. For example, monkeys may communicate their emotional state to others by making an open-mouth threat, thus indicating the extent to which they are willing to compete for resources, and this may influence the behaviour of other animals.5. Emotions enhance social bonding, for instance between parents and their young.6. The state of mood may help in the continuous interpretation of the reinforcing value of events in the environment.7. Emotion may facilitate the storage of memories, particularly so-called ‘episodic’ memories of particular events in life. Vivid memory of the circumstances surrounding a powerful reward or punishment may help to guide behaviour in the future.8. Emotion may also help to trigger the recall of memories.9. By enduring for minutes or longer after a reinforcing stimulus has occurred, emotion may help to produce persistent and continuing motivation and direction of behaviour, to help achieve a long-term goal.

Brain mechanisms of emotion

Animals are built with nervous systems that enable them to evaluate which environmental stimuli, whether learned or not, are rewarding and punishing, i.e. produce emotions that will be worked for or avoided. Sensory stimuli are normally processed in the brain to produce a ‘neutral’ representation of the object or event, before its emotional significance is decoded. For example, in monkeys, signals from the taste buds of the tongue are relayed to a region of the cerebral cortex, the ‘primary taste cortex’, in which nerve cells respond selectively to different tastes, regardless of their reward values to the animal. Then, signals are passed to the ‘secondary taste cortex’, in a region of the frontal lobe called the orbitofrontal cortex where neurons respond to the taste stimulus only if the monkey is hungry. Similarly, visual stimuli, which frequently carry information about potential reward or punishment in the environment, are initially processed in the visual parts of cerebral cortex, leading to the lower part of the temporal lobe, where objects are represented, independent of their emotional significance. Then, in structures such as the orbitofrontal cortex and the amygdala (part of the limbic system), which receive fibres from the inferior temporal visual cortex, associations are learned between the objects and the primary reinforcers associated with them.

Emotional states are thus represented in the orbitofrontal cortex and amygdala. Consistent with this, electrical stimulation of the orbitofrontal cortex or amygdala is rewarding (even in humans it produces a sensation of pleasure), while damage to these structures affects emotional behaviour, leading to inappropriate reactions to emotive stimuli.

The behavioural selection system must deal with many competing rewards, goals, and priorities. This selection process must be capable of responding to many different types of reward, which are decoded in different brain systems that have evolved at different times, even including the use in humans of language to enable long-term plans to be made. These many different brain systems, some involving implicit assessment of rewards, and others explicit, verbal, conscious evaluation and planned long-term goals, must all enter into the mechanism for the selection of behaviour. Although poorly understood, the issue of emotional feelings is part of the much larger problem of consciousness.

E. T. Rolls

Bibliography

Darwin, C. (1872). The expression of the emotions in man and animals, (3rd edn). University of Chicago Press.
Oatley, K. and and Jenkins, J. M. (1996). Understanding emotions. Blackwell, Oxford.
Rolls, E. T. (1999). The brain and emotion. Oxford University Press.

See also cerebral cortex; conditioning; consciousness; limbic system; pain; pleasure; taste; vision.