Both prosopagnosia and amusia can be caused by injuries or lesions to very specific areas of the cerebral cortex. As such, they dramatically illustrate the specialisation of cortical areas for very particular functions.. In fact, different types of amusia, specifically affecting timbre or melody or rhythm perception can be induced by lesions to different brain regions.
These kinds of highly selective neurological conditions are well known, thanks to the writings of Oliver Sacks and others. What is less widely appreciated is that they also have congenital forms, which are not associated with any kind of brain lesion. In fact, both conditions are surprisingly common – the prevalence of congenital prosopagnosia is estimated at 2.5 percent and that of congenital amusia at 4 percent of the population. They are also highly familial, with very high rates among first-degree relatives of affected people.
The mutations that cause these conditions most likely affect the connective wiring of various parts of the brain. No particular genes have yet been identified, but whatever their normal functions, their disruption seems to leave sensory processing areas unable to communicate the results of their computations to higher areas associated with conscious awareness. Genetic variation can thus affect, very literally, the way people’s brains are wired, influencing not just how people perceive various categories of objects but also, fundamentally, how they think about them.
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9 Comments
Add CommentI wonder whether or not something quite similar might be behind certain social pathological behaviors. The person has empathic neurons which still respond negatively to the harm being done to another, but those responses are not effectively communicated to the brain's moral processing areas.
Reply | Report Abuse | Link to thisI think you may have something there. I wonder if it is possible that in a few cases the connections are made to the wrong areas as well because a few people such as a couple of well know killers have a history of totally inappropriate emotional responses.
Reply | Report Abuse | Link to thisI find this fascinating because I can't carry a tune or hear when I'm off key. I also have a terrible time staying in rhythm when dancing. This is why I don't sing or dance when others are around. I also never sing around dogs because it seems to spark an attack response even in normally friendly dogs.
Reply | Report Abuse | Link to thisThere is indeed a strong parallel between the kind of disconnection syndromes I discuss here, which affect perceptual processes, and what is proposed as the underlying defect in psychopathy. Imaging research suggests a disconnection between areas involved in empathy, conscience and impulse control. See the following for more information: http://wiringthebrain.blogspot.com/2010/02/bad-to-bone-altered-connections-in.html
Reply | Report Abuse | Link to thisThese observations are entirely consistent with my completely different model of how the brain works, introduced at www.scienceuncoiled.co.uk, where you will find a summary, my book and a compilation of recent supporting evidence and research proposals. Questions to michaeltdeans@gmail.com welcome.
Reply | Report Abuse | Link to thisMy son has an interesting variation of tone deafness and I am wondering how the author would explain it. He has perfect pitch in that if he hears any note he can tell you exactly what it is. However, he cannnot carry a tune at all when singing.
Reply | Report Abuse | Link to thisMy daughter has prosopagnosia, and she is not tone-deaf, not by a long shot. I don't know if she has perfect pitch, but I do know that she has good tone and a beautiful singing voice. It does not take long for her to learn a song and sing it well.
Reply | Report Abuse | Link to thisI am bad at carrying a tune, and even worse at matching names of people to their faces. But if I focus really hard, I can detect if a tune is off (but cannot sing it right despite that). Similarly, if I only meet five or less new people in a day, I can remember all their names. Bring on a sixth one, and I lose them all. I've noticed that the problem seems to be that when I have to sing, I have a 'different' tune in my head to sing to, and there is almost never any way to get the 'right' tune back into the storage section for that tune. Ditto with names. I often store the wrong but similar name, and no amount of mnemonics seems to help. If I get any of these right the first time, there is never any problem later. Usually, it helps if I see the name of the person first, and then see the face. Similarly, if I hear the instrumental part of the tune first, before the song.
Reply | Report Abuse | Link to thisI know several people, including my young granddaughter, who can sing reasonably well in tune as long as they are singing solo. As soon as someone else joins in, however softly, they 'lose' the tune and the singing becomes a tuneless monotone - and they have no realisation of the fact. I'd love to help my granddaughter as we come from a community in which singing is a 'part of life' and her peers are beginning to make fun of her voice. Does anyone have any explanations as to why the perception of a tune is 'drowned out' as soon as someone else joins in? Is there any training which would help?
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