Hitting head, seeing stars

[Bill Kemler]

>I write for Popular Science magazine, and for a column called FYI, I'm
>trying to answer a reader's question:

>      When you hit your head and see "stars," what are you really seeing?

>Can anyone point me to an answer for that? I've tried a couple
>neurologists/head injury experts, but haven't come up with much of an
>explanation.

>Many thanks.

>PJ Skerrett
>skerrett at world.std.com

I've had students ask this same question in class.  Here's what I tell
them:

The perception of visual events occurs as a result of the activity of the
nerve cells in the visual cortex at the rear of the brain. Usually, the
activity of these cells is under the control of electrochemical nerve
signals coming from the retina of the eye via the optic nerve and thalamus (a part
of the brain that filters sensory information). However, anything that
stimulates activity in the cells of the visual cortex will produce
visual sensations. Hallucinogenic drugs, signals from other parts of
the brain (as in the case of dreams), or direct electrical or mechanical
stimulation of these cells will all produce visual sensations.

Hitting your head is an example of mechanical stimulation triggering
these visual sensations (as is rubbing your eyes hard). What kind of
visual experience you will have will depend on which cells in cortex are
most effected by the stimulation. The visual cortex contains specialized cells called "feature detectors".
Each type of feature detector normally reacts most strongly to a
particular type of visual pattern or feature. For example, there are
edge detectors, angle detectors, motion detectors, etc. When the
activity of a particular feature detector increases, we percieve that
feature. Seeing an object move across the visual field will produce
increased activity of the motion detectors cells and create the perception of
movement. A knock to the head (particularly the back of the head) may
cause these feature detectors to misfire causing the floating or
bursting "stars" of light, ghostly squiggles, and other strange effects.

Hope this helps.
 
Bill Kemler   2.31¹