"I could see, and yet, mon, I could na' see": William Macewen, the
agnosias, and brain surgery
Two little noticed cases in which William Macewen used symptoms of visual agnosia to plan brain surgery on the angular gyrus are reviewed and evaluated. In both cases he found lesions to the angular gyrus and these positive results are analysed in the historical context of the dispute over its proposed role as the visual centre of the brain.
Macewen’s first patient, Thomas Muir, was rendered unconscious in 1886 when hit on the head by a piece of falling coal. Using the words included in my title, Muir summed up what had happened to him: he could not recognise people unless they spoke, he could distinguish his Bible only by the embossing on its cover, etc. This agnosia lasted only two weeks, after which he was seized with paroxysms of left-sided head pain that alternated with periods in which he had almost uncontrollable impulses to kill his wife and children. Macewen discovered Muir’s ‘alexia’ when he saw him for these homicidal impulses, eleven months after the accident, and concluded that it clearly indicated a lesion in “the posterior portion of the operculum or in the angular gyrus.” He found part of the internal table had separated and was pressing on the supramarginal convolution with a portion of it having been driven into the angular gyrus. The bony growth on that piece was removed, the bone replaced, and the wound dressed. When the wound healed Muir’s homicidal impulses disappeared.
Macewen’s second patient, ‘J.C.,’ was a fifty-two year old businessman seen in 1892 for a purulent mastoid discharge. Macewen found symptoms of cerebellar abscess and also that J.C., although not aphasic, could only understand what was said to him by guessing at the speaker’s intent. Slightly later, J.C.'s symptoms became worse in that he became unable to understand what he saw. Now describing him as ‘psychically blind’ as well as ‘word deaf,’ Macewen suspected there was a cerebral abscess pressing on the angular gyrus and the first temporal convolution as well. Four days after treating the cerebral abscess, J.C.'s visual agnosia disappeared, and four days later again he understood speech.
Published, unpublished, and manuscript material on the cases and their follow-up is presented and the significance of Macewen’s changing descriptions of the symptoms and their bases explored.
Session II -- Visual Neuroscience
Montreal, Quebec, Canada