Imaging the brain at multiple scales: how to integrate multi...
What does blue taste like? – The blending of senses.
What colour is the letter W? What does yellow taste like? These are not usual questions you hear, however, for some people it is an everyday aspect of their life to deal with. For these individuals their senses are somehow joined together, which is unpronounceable termed as the neurologically-based condition synaesthesia (1). When concerned with this syndrome, “the stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway” (1). For years, synaesthesia was dismissed as the product of someone's overactive imagination. But in the past decade, researchers have documented a numerous amount of cases of otherwise ‘normal people’ – who have these extraordinary blended senses (1).Daniel Eaton is such a case, when he reads a book the numbers and letters appear in specific colours(2). What we see in black and white automatically pops off his page in various colours. This common form of synaesthesia is known as ‘grapheme’ (colour synaesthesia) where letters and numbers are perceived as inherently coloured (1). Colour synaesthesia could also occur in relation to sound, where the barking of a dog or piano-music triggers a certain colour along with simple shapes that might arise, move around and fade again when the sound stimulus waves off (1).
A numerous amount of synaesthesia types are possible since the intertwining of all our different senses can occur. One of these is the ‘ordinal linguistic personification’ form where numbers, days of the week or months evoke personalities (1). For instance a synaesthete says; “T’s are generally crabbed, ungenerous creatures, 9 is a dark, a gentleman, tall and graceful” (1). Another type of synaesthesia is when numbers, months or years elicit precise locations in space, an example could be that 1980 is visualised ‘farther away’ then 2010 (1). An additional rare form is the one concerned with the gustatory sense, individual words and the phonemes of spoken language induce a taste sensation in the mouth, for example “Daphne sounds rather bitter while William has a few ginger elements" (1).
There are several theories to the cause of synaesthesia. Functional neuroimaging studies (using fMRI’s which scan the brain and show the activated brain area) demonstrate significant differences between brains of synaesthetes and non-synaesthetes (1). One theory posits that irregular developing of new neural connections within the brain leads to a breakdown of the boundaries that normally exist between the senses (1). So synaesthesia could be the “collective "chatter" of sensory neighbours once isolated from each other” (1). Another theory is that all infants begin life as synaesthetes, born with immature brains that are highly malleable (1). Connections between different sensory parts of the brain exist that later become ‘blocked’ as the infant matures. Still, another theory states synaesthesia doesn't require any extra connections, but arises when normally hidden channels of communication between the senses are "unmasked" and cross into conscious awareness (1).
Unfortunately, we do not yet have the technology to observe brain-connection changes in humans and determine how they relate to mental changes, therefore none of these theories can be tested experimentally (1). Apart from the isolation and misunderstandings synaethetes might experience during social interactions, there are luckily some advantages to the fusing of senses. For instance some researchers believe synaesthesia gives a person a superb memory as found in one of the most extraordinary cases (Elisabeth Sulzer) who has more forms of synaesthesia (2). In only the few tests recently done the discoveries dazzled the researchers with the incredible ability of the woman’s long-term memory. It is a very interesting field, however, difficult to explore, not only the study of synaesthesia is useful but also because studying this will give insights into other questions, such as how the brain combines information from different sensory modalities.
Given synaesthetes' extraordinary conscious experiences, researchers hope that their study will provide better understanding of consciousness and its mechanisms (1). All in all future research could give us ground-breaking knowledge and insights in to our ever so fascinating and mystical brain.
(1). Harrison, J. Synaesthesia – The strangest thing . Oxford University Press: New York, 2001.
(2). ABC news. Synaesthesia – Trick of the Senses Part 1. Good Morning America: Washington DC. 2006.