What is behaviour?
Behaviour is a complex but essential aspect of animal biology. It can be difficult to define as it encompasses many aspects of biological function, but can be considered to be the way in which an individual interacts with a given environment or situation. Manifestations of behaviour include physical movement and production of various signals, from secretion of scents to changes in skin colouration to more advanced phenomena including speech.
Why is behaviour important?
The importance of behaviour depends upon the context in which it occurs. Sometimes behaviour determines how individuals of different species interact, a good example of which is the relationship between predators and their prey. When considering interactions within a given species, behaviour is essential for fundamental processes such as reproduction; successful mating not only requires correct function of the gonads but also the choice of mate. Continuing the reproductive theme, behavioural relationships between parents and their offspring are also critical and, as any mother or father will tell you, the bond formed with a child is extremely powerful. In many species, social interaction and hierarchy are also important in daily life. Such social interactions can be observed from invertebrates through to human beings. Behaviour has many implications for humans and strongly influences key aspects of our lives including the formation of friendships, choice of sexual partners, performance at work and management of conflicts.
How does behaviour work?
Most aspects of behaviour are controlled by the brain and/or hormonal system, hence its interest to neuroendocrinologists. Due to its complexity, it is difficult to provide any single mechanism for how behaviour works. However, below are some examples of how behaviour links with other neuroendocrine processes.
Sex: Steroid hormones (e.g. oestrogen, testosterone) produced by the gonads not only control gonadal function but also regulate behaviours, e.g. aggression. Following birth, certain hormones control parental behaviours; for example, the hormone prolactin is not only essential for milk production, but also regulates aspects of maternal behaviour.
Stress: We are all aware that our behaviour can change in stressful situations. There is growing evidence to suggest that stress, acting via hormones such as cortisol, can influence reproductive behaviour, social interactions, appetite and the response to substances of abuse. Prolonged stress may also lead to behavioural disturbances such as depression.
Obesity: It is now well established that the gastro-intestinal tract secretes multiple hormones that act on the brain. These hormones control satiety (i.e. how full or hungry we feel) and also the emotional and hedonistic responses to feeding.
Body clock: One of the most obvious behaviours is the daily sleep-wake cycle. Although our need for sleep is partly determined by the length of time that we have been awake, it is also driven by our internal daily (circadian) clock.