The Homunculus is a model of the human body which reflects the amount of brain tissue dedicated to each part. This means that body parts with more sensory and motor nerves are enlarged and parts with less enervation are shrunken. The result of distorting body scale in this way is a bizarre and grotesque figure which is both provocative and scientifically significant.
Scientists describe two homunculi: the "sensory homunculus" reflective of the somatosensory cortex and the "motor homunculus" reflective of the motor cortex. Below is a depiction of each with the sensory in blue and motor in red.
You may notice that the head-tail organization of the body is seen in the brain as well. The cortexes are spread out between the mouth and anus on the lateral and medial sides. The head-tail organization of the body is our earliest spatial orientation, developmentally and evolutionarily, so it makes perfect sense that the brain would reflect that.
You can also see that the brain tissue is not flat but has a branching structure, which links nearby and coordinated parts according to proximity and function. Looking directly at the brain’s structure reveals some interesting things that the Homunculus ‘little person’ model doesn’t.
For instance, the person-like model has enormous fingers which are almost 50 times the size of its arms. Lots of brain space is devoted to the fingers because they are involved in many complex and frequently used functions. At a glance it may seem that the arms are insignificant, but this could not be further from the truth. The brain tissue which controls the arms is the base which supports the tissue controlling the hands and fingers. The torso structure in turn supports the arms and is in turn supported by the head-tail structure of the spine. In essence, the branching structure of the cortex shows a branching hierarchy of physical function not immediately apparent in the model of the Homunculus.
But even this branching model does not reflect the overlapping functions of different brain tissues. Direct stimulation of the motor and sensory cortexes in studies has shown that regions are not separate and discrete but blended with a high level of overlap in connections.
In short, the search for visual representations of sensation and awareness continues.
For further reading check out the scholarly articles below. Both expand on the homunculus in exciting ways:
“If truly drawn according to cortical mapping evidence, [the homunculus] could never have been recognized as near humanoid -and yet, they note it is because of these pictures that it has attained its educational and practical longevity”
The figure of the homunculus has new stories to tell about normative biomedical bodies and the imbrication of gender, disability, race, and class in their renderings. In particular, critical scholarship of biomedical psy/sciences, especially feminist work, offers many accounts of the ways biomedical renderings of the normal body or brain both reflect and constitute socially normative ideologies of embodiment and personhood.
The word “Homunculus” first became popular in sixteenth-century alchemy. At the time, many people believed in ‘preformationism,’ the idea that organisms develop from miniature versions of themselves. According to this defunct model, all life was fully formed at the beginning of time and only had to grow in size like living, breathing Magic-Grow dinosaurs.
For instance check out this wild and inaccurate drawing: