Sunday, February 14, 2010

The specificity of synaesthetic memories

Synaesthesia is a condition in which experience in one modality (for example auditory) triggers an experience in another (for example vision). Commonly a specific note or number generates a specific colour. This naturally argues for a very specific set of connections in the brain – from say a specific part of the auditory cortex to a specific part of the visual brain - in fact to the colour centre (V4). And not only to any part of V4, but the part in which that specific colour is generated and registered. [It is known that there are groupings of cells in V4 that prefer specific colours].
But if my experience is anything to go by, synaesthesia also affects memory in highly specific ways.

I often listen to BBC Radio 4 in the evening, just before the shipping forecast at about 23:45 and the news at midnight. The shipping forecast is preceded by a tune known as sailing by. I cannot be the only one in whom the music conjures up the sea and a boat – that, after all is the title of the tune. But the mental image the music triggers in me – which is always very clear – is also very precise. It is not, as one might imagine, of the rough seas around the British isles, but of a clear, azure blue sea, more like the sea one encounters in the Aegean, around the Greek and Turkish coasts. The boat I see is not any boat but an old fashioned one, of which a perfect example can be seen here. And I am always looking from the boat at the sea.

I have been listening to this tune for years and the mental visual image it creates has never changed. This argues for a highly specific set of connections that link the visual memory system with the immediate auditory input. Experts might have other terms to describe the phenomenon; for all I know it may not even fall under the term synaesthesia. But whatever term one might choose to describe it, the fact remains that it is testament to an astonishing specificity in cortical connections.

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