GRWLXS

Through the famous case of Phineas Gage, a patient with severe frontal lobe damage, Antonio Damasio (1) locates the somatic markers in the frontal cortex.
An injury of the frontal lobe can lead to deficits in executive function, such as anticipation, goal selection, planning, sequencing, monitoring, and self-correction. (2)The frontal areas of the cortex are inhibitory in nature: If the frontal area is damaged, the ability to inhibit socially undesirable behaviours, like uttering obscenities is diminished.’

The Prefrontal Cortex

What about those distinct shapes of the different Grawlixes in cartoons?

Consider some of the effects of a seizure for patients with Frontal lobe epilepsy. (3)A quick comparison with the available Grawlixes shows a lot of similarities.

The symptoms typically come in short bursts that last less than a minute.
During the onset of a seizure, the patient may exhibit abnormal body posturing.
In rare cases, uncontrollable laughing or crying may occur.
In most cases, a patient will experience a physical or emotional Aura of tingling, numbness or tension prior to a seizure occurring.
An aura sensation can include some or a combination of the following:

Bright lights and blobs
Zigzag lines
Vibrating visual field
Kaleidoscope effects on visual field
auditory hallucinations
Modification of sounds in the environment: buzzing, tremolo, amplitude modulation
Feelings of confusion
Feeling as if you are getting warmer or overheating
Sudden Perspiration
Weakness, unsteadiness
Being unable to speak properly, such as slurred speech or gibberish.

I think it is not far fetched to see Grawlixes as a product of the frontal cortex.
We can assume that most of the times Grawlixes are uttered, there is no case of  frontal lobe damage. And since they often seem to replace profanities, it implies that some of the  Grawlixes are themselves an exaggerated version of the control mechanisms that inhibit the expression of profanities and undesirable behaviour.

Grawlixes and D.I.Y. Frontal Lobe Stimulation; A Shortcut to Enlightenment.

The illuminating effects of prefrontal lobe ¬stimulation were already familiar with several agents in the field..

Max Taber (One flew over the cuckoo's nest 1975) after an illuminating moment  tuning up his frontal lobe to prevent himself from completely losing control.

The three stooges (inspired by Laurel and Hardy and James Finlayson) were well-known forehead-slappers. Here also  appealing to the self-correcting  qualities.

Homer Simpson,  reinforcing that the answer was always right in front of him, d’oh!.

Again, Sjef van Oekel  just discovering diy illumination and is seeing some nice squeans and spurls .("Doctor; everytime I do this (*) I  get  a buzzing headache!")

from;
http://the-euclideanfly.blogspot.nl/

(1) Antonio Damasio . Descartes' Error: Emotion, Reason, and the Human Brain, Putnam Publishing, 1994, ISBN 0-399-13894-3
(2) http://en.wikipedia.org/wiki/Frontal_lobe_injury
(3) http://en.wikipedia.org/wiki/Aura_(symptom)
Gwillim law. Grawlixes Past and Present ; http://www.statoids.com/comicana/grawlist.html
Walker, Mort. The Lexicon of Comicana, ISBN 0-595-08902-X