Alexia sine agraphia

In his excellent book, ‘The Mind’s Eye,’ Oliver Sacks discusses the strange case of one of his patients, Canadian author Howard Engel, who woke one morning to find the front page of his newspaper printed in an unidentifiable, ‘Oriental’ script. At first thinking he was the victim of a practical joke, he was dismayed to find the entire newspaper in the same state as well as all other written material he looked at.

Howard was admitted to hospital and was found to be suffering from stroke-induced alexia sine agraphia, also called pure agraphia, a neurological condition affecting part of the brain involved in reading. Thankfully for his profession, Howard could still write but could no longer read his own writing, making editing of his work a problem.

The VWFA is in the temporal lobe (image by Scott Camazine).

Pure alexia is caused by damage to a small region in the left hemisphere of the brain called the visual word form area (VWFA). It can lead to some bizarre outcomes. Some sufferers lose the ability to read one script but retain the ability to read a second (this is more frequent in Japan where two different scripts, Kanji and Katanka, are in common use). Other sufferers are able to sort words they cannot consciously read into basic categories, such as living and non-living. This implicit, sub-conscious understanding of word meaning may indicate that other regions of the brain (possibly the VWFA-equivalent region in the right hemisphere) perform some reading function.

Although damage to the left hemisphere has been associated with pure alexia since the 1890s, the precise location of the VWFA was not identified until 2000. The concept of a distinct brain region responsible for reading has been a source of dispute for some time. Writing has existed for a few thousand years and widespread literacy for a hundred years or less, far too brief, dispersed and complex a task for evolution to have created a dedicated brain region. Alfred Wallace, the co-discoverer of evolution, was troubled by this apparent paradox and believed it was evidence of God.

The Great Wall of China Fallacy

Image by Samuel Li

Imagine you are a tourist admiring the Great Wall as it snakes over mountains and valleys when the loud man next to you tries to strike up a conversation.

“Isn’t it amazing how the landscape has formed over millions of years to exactly match the contours of the Wall,” he says. “It’s clear evidence of existence of God.” The man is obviously insane so you nod politely and move quickly away while he fiddles with his camera.

Similarly with the VWFA, the assumption that the structure of the human brain has evolved to accommodate reading is flawed. It is writing systems that have been adapted over thousands of years to make best use of the brain. Despite independent origins, all of the world’s major writing systems share common characteristics such as clearly defined lines and junctions that assist with reading. These characteristics exploit the abilities of the VWFA which may have originally evolved for face and object recognition.

Some writing systems are exceptions. Braille, designed to be read by touch, is an obvious example. One of the great mysteries of the Inca is how such a vast and complex civilization was able to function without a writing system. However, there is growing evidence that quipu, colourful knotted strings originally thought to contain numerical information, were actually a three-dimensional writing system unlike any other ever devised.

Advertisements
This entry was posted in Science and tagged , , . Bookmark the permalink.