Pathomechanisms
| Author: Markus Dahlem | 01. February 2006 |
| Edited by: Markus Dahlem |
Whitman Richards
Whitman Richards is a professor of Cognitive Science at the MIT Artificial Intelligence Lab. He focuses on high-level vision and the question of how perceptual knowledge is represented and structured.
Simple (left) and complex (right) fortification pattern. © 1971 Scientific American
In 1971 Richards wrote in the popular Scientific American about visual migraine aura. He suggested that the zigzag as part of a visual aura is caused by the spatial layout of a specific type of neurons in visual cortex. Neurons that are specialised in detecting edges with a certain oriented were known since the work of Hubel and Wiesel (see the next article for a more detailed description). A hexagonal grid arrangement of domains with iso-orientation can explain the angles in the zigzag pattern, argued Richards.
At that time the two-dimensional layout of iso-orientation domains was only coarsely measurable on the basis of electrophysiological experiments (Albus, 1975). It became of interest to establish a geometrical relationship between the iso-orientation domains. A precise description of the migraine aura was hoped to provide first hints to this important question of cortical organization.
It took almost 20 years to reveal the true spatial organization of iso-orientation domains (Swindale et al., 1987; Bonhoeffer and Grinvald, 1991). The layout of the orientation map that Richards suggested turned out to be a pattern close to the real arrangement of orientation selective cells around pinwheel centers in the primary visual cortex. But even more importantly, Richard's main idea, i.e., that the aura pattern reveal the functional organization of human cortex, is still not fully explored. Yet in the face of the plethora of aura symptoms together with the increasing success in computational investigations of brain functioning a renaissance of this idea is upcoming.
"Thanks for having this site. I've had the scintillating scotoma since I was in my early 20's, and I'm now 49. My dad had the same thing. I remember him mentioning an article about it in Scientific American magazine when he described it to me (probably in the early 1970s). A few years later I started to experience it also, but could never remember the name of it. I've searched the internet for some clues a couple of times in the past, but finally, today, I found your site, which seems to have more information than any other. I was never too concerned about having these, since I did remember my dad saying that it was something that happened in the brain. Mine don't come too often (at the most once a year) and I've never had any pain or other uncomfortable feelings along with it. I have suspected that stress or fatigue contributed to it, but wasn't always sure. After reading some of the other posts, I feel thankful that mine are very innocuous."
(Lois, Edith Frost's Homepage, February 3, 2004)
"A very good article on migraine visuals appeard in Scientific American sometimes in the early 70s. It was the first time anyone believed that I really had migraines and not flashbacks. I had been having visuals for several years & attempts to describe them to people, including medical people, resulted in my being dismissed as a flaky druggie. Little did I know what kind of company I was 'really' in, like Juliana of Norwich, & various other saints who took the auras for visions.
My migraines have changed forms several times. I currently get the visuals without the headaches approximately 50% of the time, but even tho I don't always have the headaches, I always have disorientation, blank spots in my vision, & trouble putting words together to make sentences when I am having a migraine. It isn't always pain that makes people disbelieve you've having a problem. Try driving with rainbow auras flashing & jagging in your vision, or trying to figure out what is really in that place in your line of sight where there's 'nothing'. Not to mention trying to tell somebody something & having your brain refuse to make the words you want."
(Jane Gallion, Newsgroups: alt.support.headaches.migraine, Subject: This Little Paper, December 17, 1997)
References
Albus K. A quantitative study of the projection area of the central and the paracentral visual field in area 17 of the cat. II. The spatial organization of the orientation domain. Exp Brain Res 1975; 24: 181-202.
Bonhoeffer T, Grinvald A. Iso-orientation domains in cat visual cortex are arranged in pinwheel-like patterns. Nature 1991; 353 (6343): 429-431.
Richards W. The fortification illusions of migraines. Sci Am 1971; 224: 88-96.
Swindale NV, Matsubara JA, Cynader MS. Surface organization of orientation and direction selectivity in cat area 18. J Neurosci 1987; 7: 1414-1427.
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