The homunculus is commonly used today in scientific disciplines such as psychology as a teaching or memory tool to describe the distorted scale model of a human drawn or sculpted to reflect the relative space human body parts occupy on the somatosensory cortex (the “sensory homunculus”) and the motor cortex (the “motor homunculus”). Both the motor and sensory homonculi usually appear as small men superimposed over the top of precentral or postcentral gyri for motor and sensory cortices respectively.
The homunculus is oriented with feet medial and shoulders lateral on top of both the precentral and the postcentral gyrus (for both motor and sensory). The man’s head is depicted upside down in relation to the rest of the body such that the forehead is closest to the shoulders. The lips, hands, feet and sex organs have more sensory neurons than other parts of the body, so the homunculus has correspondingly large lips, hands, feet, and genitals.
The motor homunculus is very similar to the sensory homunculus, but differs in several ways. Specifically, the motor homunculus has a portion for the tongue most lateral while the sensory homunculus has an area for genitalia most medial and an area for visceral organs most lateral. Well known in the field of neurology, this is also commonly called “the little man inside the brain.” This scientific model is known as the cortical homunculus.
The idea of the cortical homunculus was created by Dr. Wilder Penfield. He used a similar image to depict the body according to the areas of the motor cortex controlling it in voluntary movement. Sometimes thought to be the brain’s map of the body, the motor homunculus really is a map of the proportionate association of the cortex with body members. It also reflects kinesthetic proprioception, the body as felt in motion.
Penfield’s motor homunculus is usually shown as a canonical, 2-D diagram. This is an oversimplification, as it does not show the original data Penfield collected from patients undergoing surgery for epilepsy. This simplification suggests that lesions of the motor cortex will give rise to specific deficits in specific muscles. This misconception is not necessarily the case: lesions produce deficits in groups of synergistic muscles. It suggests that the motor cortex functions in terms of overall movements as entire libraries, rather than how to move individual muscles, allowing a great deal more complexity.
How your brain sees your body: Meet the cortical homunculus
By Esther Inglis-Arkell, 2010
We all know what bodies look like from the outside. This cortical homunculus is how your brain sees your body from the inside.
In the 1930s, Wilder Penfield performed surgeries on patients with epilepsy. While he had a live brain on the table, he figured he might as well poke around a bit. The doctor gathered data, finding out which parts of the cerebral cortex control which voluntary body functions and feeling. What he discovered was a vastly distorted view of the human body: the cortical homunculus.
The cortical homunculus represents the importance of various parts of your body as seen by your brain. There is little need for the brain to know what’s going on in the arms and legs. All these limbs need to do is stay out of an open flame and get your hands and feet to the right places. The hands, the tongue, the genitals, and the facial features are extremely important, and give people a ton of sensory information. As a result, they take up a lot of brain space.