Homunculus Man

The rather unfortunate chap pictured above is called Homunculus Man. He’s a visual representation of a man (I couldn’t find a Homunculus Woman) based on the neurological ‘map’ within the sensory cortex. The reason he looks a little different from us is that he’s taken on the proportions of the brain that processes sensory functions for different parts of the body and the importance the brain assigns to them.

The brain maps each sensory receptor on to the cortex so the more receptors there are on the skin, the larger that area will be on the surface of the cortex and the size of each part of Homunculus Man’s body is related to the density of sensory receptors. The more we use a part of our body, the bigger area is given over to it in the sensory cortex, hence over-sized hands, fingers, lips, tongue and genitals.

A fun house mirror reflecting an unfamiliar image back to us.

Some people have speculated that this also correlates to our ability to survive and what we need to feed, shelter and protect ourselves - hand dexterity for gathering food and hunting, tastebuds to discern food, smell, vision and hearing.

Granted, this man is only a very general representation as everyone will be different; a football player will have a different patterning than a tailor and modern man will be very different to our ancestors. MRI scans have found that London taxi drivers have a larger than average hippocampus. In order to gain their licence, they must train to for ‘The Knowledge’, which requires them to memorise roughly 20,000 landmarks and study 320 routes and 25,000 streets.

So what does this mean for you? It’s another example of our brain’s plasticity (the ability to adapt and change), meaning what we do impacts how well we can do it - the use it or lose it law that sensory input drives motor output. Changes occur mainly in our brain, not our muscles; skill learning and memory alter the information that the brain sends out to the muscles, thereby changing the movements that are produced.

We often hear the term ‘muscle memory’, yet what we’re really saying is the more we do a movement, the larger and more attuned that area of the cortex will become.

Pavlov demonstrated the basic principle of classical conditioning with dogs.
A neutral event, such as ringing a bell, could be associated with another event that followed - being fed.

‘Smudging’ is another change which is known to occur in the cortex, where brain areas normally devoted to different functions or different body parts start to overlap due to pain. This may be a strategy the brain uses to make nearby body parts sensitive (smudging of sensory areas in the brain) or to make a body part more difficult to use (limiting movement by smudging the motor areas in the brain). The longer the pain persists, the more advanced the changes become in the brain and may well explain why people still feel pain long after an injury has healed.

This was famously illustrated by Pavlov’s dogs and their learning through association. A bell was rung before the dogs were given dinner, which led to them salivating after hearing the bell ring. Just as the dog learns this connection between the bell and dinner, if the bell isn’t rung it eventually unlearns this connection.

The same is true for those of us who have learned to associate certain movements with pain; eventually you will stop feeling pain if you do the movement you’ve been avoiding without causing re-injury.

- F

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