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Name: ___________________________
Anatomy & Physiology
Date: ____________
Period: _____
The Homunculus
Scientists can map which parts of the brain control various parts of the body. The mapping is
done by stimulating the sensory or motor cortex with a weak electric current. The stimulation
often produces tingling or movement in part of the body.
Humans put great emphasis on speech and manipulation of objects by the hands, so humans have
large amounts of cortex devoted to mouth, tongue, and hands. Different species have different
patterns. Rats get a lot of information from their whiskers, so they have large amounts of sensory
cortex devoted to their whiskers.
The following diagram represents a slice of cortex near the fissure of Rolando, running from the
top of the head down toward the ear. The diagram indicates the location and amount of cortex
devoted to each part of the body. At location #22, for example (just above the lateral fissure by
the ear), stimulation produces a swallowing reflex. A location #3, at the top of the head,
stimulation results in toe movement. Altogether, the map of brain connections to the body in this
particular strip of cortex looks like this, with the amount of cortical tissue represented by the size
of the body part in the diagram:
How is the homunculus
mapped out?
The diagram looks a bit
like a grotesque little man,
so it is called the
homunculus (ho-MUN-qlus) which means "little
man" in Latin. The first
homunculus diagram was
drawn by Wilder Penfield
in the 1940s and looks
similar to the one above.
Notice that the hands, lips,
and tongue are large,
because of the large areas
of cortex devoted to these
areas of the body in
humans.
Name: ___________________________
Anatomy & Physiology
Date: ____________
Period: _____
What sort of humorous references to the homunculus are common?
The homunculus is a textbook diagram, certainly is not a self or center of consciousness in the
brain. However, humorous references to the homunculus as a little person in the head are
common among psychologists. One psychologist might say to another, "But how exactly is this
mental activity carried out? Does the homunculus do it?" This is a way of saying, "You have not
given us an adequate explanation!"
What is evidence that cortical mapping can change with experience?
Actually there are many homunculi in the brain, if the word refers to an area of cortex where
body surfaces are mapped. Such maps can change with experience. People who read Braille
(which is done with an index finger) develop large areas responsive to stimulation from the index
finger. A homunculus mapped on the motor cortex of such a person would have a huge index
finger.
This flexibility in the brain inspired some therapies for brain-damaged patients. In one study,
people who suffered partial paralysis of an arm after a stroke were able to regain full use of the
arm by having the other (good) arm immobilized (prevented from moving). This encouraged
development of the cortex that controlled the "bad" arm, resulting in partial recovery of the
patient's ability to move that arm.
In the space provided below answer the following questions IN YOUR OWN WORDS:
1. What is the “homunculus”?
2. How to sensory neurons relay information to the brain?
3. When the brain receives a signal, what happens?