Motivated Behaviour and the Role of the Hypothalamus

The behaviours of eating and sexual activity in humans are regarded in terms of motivated behaviour such that they appear to be purposeful and directed toward a goal. The hypothalamus is a brain structure located deep within the brain that, although small in size less than 1% of the brains total mass, is largely responsible for and controls a wide variety of human behaviour including motivation, eating, sexual activity and emotion. However in trying to understand this role it is important to first investigate the fundamental reasons and causes behind motivated behaviour. One apparent reason for behaviour is that we act out of free will however this is not a viable cause of behaviour as sometimes the central nervous system produces behaviour, which cannot be due to free will. Hebb (1955) and Heron (1957) argued that in order for the brain to maintain a minimum level of interaction people are motivated to engage with stimuli present within the environment. This is known as environmental stimulation and was examined through a series of experiments focusing on sensory deprivation. Hebb (1955) set up a cubicle in which subjects were deprived of nearly all sensory input such as sound, sight and touch for 24 hours. The results showed that for 4-8 hours the subjects were content just to "enjoy the peace and quiet" (Kolb & Whishaw, 2001) as they were instructed to do. However beyond this time set subjects became increasingly distressed and developed a significant need for stimulation of any kind. Hebb (1955) concluded that since all the basic needs of the subjects were met and they were still distressed, the brain must therefore have an intrinsic need for stimulation, which could explain the causes of behaviour.

However the brains inherent need for stimulation is not the only reason for behaviour. There is also an internal, energising factor that drives behaviour and is known as instincts or drives. The ‘Flush Model' represents the notion that behaviour is caused by

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