What is like being a researchbiologist in Singapore? Singaporeis an extremely attractive place tolive and work for both Asians andnon-Asians. English is spoken byeveryone and it has become a veryappealing place for Asian (typically,but not exclusively, Chinese andIndian) and non-Asian (from NorthAmerica, Europe, Australia andNew Zealand) researchers trainedelsewhere to move to. For theAsians, this is home or close tohome, while non-Asians get toexperience a different culture, byliving and working here. There hasalso been a tremendous push toraise the profile of life sciences inschools and colleges. Variousscholarship and fellowshipschemes have been instituted bygovernmental and private agenciesto encourage more Singaporeansto take up higher education in thelife sciences.

By capitalizing on all thesefeatures, Singapore hopes tomake life-science-based industry amajor focus of its economy. Thegovernment, as well as otherorganizations have invested a greatdeal into the life sciences. The‘Agency for Science, Technologyand Research’ has been mandatedwith effecting the biomedicalrevolution and runs a number ofinstitutes carrying out biomedicalresearch. Then there are theuniversities, which are alsoinvolved in life science research.

I work in an exceptional institute— the Temasek Life SciencesLaboratory — run by Drosophilacell biologist Bill Chia. We broadlyfocus on cellular anddevelopmental biology, where ourinvestigators are involved incuriosity-driven-research using avariety of model organisms,covering plant, animal, fungi andbacteria. The majority of activity inall research organizations is intraining manpower and ingenerating intellectual property.The impact of Singapore’s lifescience investments onbiotechnology industry andeconomy should come soon andthis will make it satisfying foreveryone involved. I certainly thinkwe are moving in the right direction.

Temasek Life Sciences Laboratory, 1Research Link, The National Universityof Singapore, Singapore Quick

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Quick guide

SynaesthesiaCatherine Mulvenna and Vincent Walsh

What is synaesthesia? It refers towhen an individual experiences asense other than the one beingstimulated. This unusual pairing isautomatic, present since childhoodand consistent across time. Aspecific experience will beactivated by the same stimuluswith a seemingly arbitraryconnection. For example the sightof the letter ‘q’ may always activatethe experience of a deep redcolour; or a middle C played on aviolin may always activate theexperience of the taste of tuna. Thepairings can be more complex forsome synaesthetes; for example, asequence of pitches may activatethe sensation of “gold, yellow andwhite moving rapidly upwards andat an angle to the right, like arippling stream”. The condition isalso referred to as ‘sensory cross-activation’.

What isn’t it? It does not apply toforced or acquired associations,such as the word Christmas havingconnotations with the colour red,the smell of mince pies or thegeneral sound of Christmas carols.It also does not include sensationstriggering memories, such as asong eliciting the memory of aperson or place.

Who first discovered it? The firstknown reference to synaesthesia inscientific writing is John Locke’saccount of a blind man whodescribed the colour scarlet as “thesound of a trumpet” in 1690.Similar isolated case-studiescontinued for some time, and itwas described in detail by FrancisGalton at UCL in 1883. Since thensynaesthesia has suffered repeatedwaves of dismissal as a phantomcondition, despite continual reportsof its existence. It is only relativelyrecently, with the application ofbrain imaging techniques, that ithas gained creditability in thescientific world as a genuine

neurological condition, and thisacceptance has led to the currentsurge in synaesthesia research.

How do we know it is real?Sensory cross-activation in thebrains of synaesthetes has nowbeen observed by positron-emission tomography (PET) andfunctional magnetic resonanceimaging (fMRI). Activation of brainregions associated with visualperception was observed inblindfolded synaesthetes listeningto words that evoked visualexperiences. These activationswere shown to be clearly differentfrom those evoked in either non-synaesthetes or the samesynaesthetes listening to tones thatdid not evoke visual experiences.Activation of areas stronglyassociated with the perception ofcolour was observed in a group ofword–colour synaesthetes. Thiswas not observed in non-synaesthetes, even after they weretrained to associate pairings ofwords with colours. Currentinvestigations are examining if thisneurological trend is observableacross subtypes involving othersenses.

What causes it? One theorysuggests that, rather thansynaesthesia being caused byextra connections ‘growing’between sensory areas, theapparent cross-activation could bea result of reduced apoptosiswhich aids differentiation of thesensory areas of the brain in thefirst months after birth. Because ofthis increased sensoryconnectivity, some experiencesbetween certain senses in infancymay stay fixed in the brain. If this isthe case, we were all synaesthetesat one stage, but sensorymodularity developed moreexplicitly in non-synaesthetes.

Is it a help or a hindrance? It isvery rare that synaesthetes’experiences are so strong they areproblematic. Synaesthetesfrequently report it as a pleasantexperience that they would preferto have, given the choice. They canfind it difficult to accept how otherpeople do not experience it, and donot think of it as surreal or unusual.The cross-activation often acts as

an additional cue in memory. Forexample, if you experience coloursfor specific months, you may notremember exactly when somethinghappened, but you may rememberit was, say, a light blue month so itmust have been October. Onefrequently reported advantage isthe use of activated colours toremember phone numbers bynumber-colour synaesthetes.

From case studies over the lasttwo centuries, a profile of cognitive

traits has emerged that is believedto be associated with havingsynaesthesia, but these requireproper investigation. The traitsinclude higher intelligence, left-right confusion, better spatialmemory, poorer spatial navigationand higher levels of creativity.

How many types of synaesthesiaare there? In theory, synaesthesiacan occur between or within any ofthe senses. The most commonlyobserved atypical activation iscolour, and the most commonstimuli to cause it are days of theweek or letters of the alphabet.Individuals may have severalsubtypes of synaesthesia —music-colour, letter-taste, day-colour, music-shape and so on —or just one. It is uni-directional, so ifnumbers activate colours, colourswill not (necessarily, but seeCohen-Kadosh et al.) activatenumbers.

How many people havesynaesthesia? This is acontroversial area of synaesthesiaresearch. The first estimate in 1883was that this affects 1 in 20 people,which fluctuated to 1 in 250,000 bythe 1980s. A pioneering study byBaron-Cohen and colleagues in1996 was the first to investigatethis issue empirically, and foundthat at least 1 in 2000 people havesynaesthesia. Following this,estimations have continually risenand current large-scale screeningsof the populations indicate asmany as 1 in 30 people experienceat least one subtype ofsynaesthesia. It also shows apattern of running in families andinitial genetic investigationssuggest in some cases at least itmay be an X-linked trait.

Will I ever experience it? Youeither have synaesthesia or you donot. Similar states have beenreported from users ofhallucinogenic drugs such as LSD.But this is widely believed to havea different basis, as the apparentactivation between senseschanges from time to time acrossdifferent uses of the drug. Whiledifferent synaesthetes havedifferent pairings from each other,one of the defining characteristicsof the condition is that each

synaesthete’s own pairings remainthe same over time.

What is the relationshipbetween synaesthesia andcreativity? It seems thatsynaesthesia is experienceddisproportionately by artists,writers and musicians. Thecomposer Olivier Messiaen(1908–1992), for example,described his experiences in detail:“Colours are very important to mebecause I have a gift — it is not myfault, it’s just how I am - whenever Ihear music or even if I read music, Isee colours”. The persistentconnection with creativity is nowbeing re-examined. Individualsidentified as having synaesthesiaare being compared to individualswithout the condition onrecognised psychological tests ofcreativity and initial results doindeed suggest that synaesthetesmay have a greater aptitude forcreative/abstract thinking. As asynaesthete might say, for furtherdevelopments, “watch this space”

Where can I learn more?Baron-Cohen, S. (1996). Is there a normal

phase of synaesthesia in development?Psyche: An Interdisciplinary Journal ofResearch on Consciousness. Vol 2(27).

Baron-Cohen, S., Burt, L. Smith-Laittan, F.Harrison, J., and Bolton, P. (1996).Synesthesia: Prevalence and similarity.Perception 25, 1073–80.

Baron-Cohen, S. and Harrison, J.E. (Editors)(1997). Synaesthesia: Classic andcontemporary readings. Cambridge,Massachusetts: Blackwell Publishers.

Cohen-Kadosh, R., Sagiv, N., and Linden,D.E.J. (2005). When blue is larger than red:colours influence numerical cognition insynaesthesia. J. Cog. Neurosci. in press.

Galton, F. (1883). Inquiries into human facultyand its development. London Press.

Nunn, J.A., Gregory, L.J., Brammer, M.,Williams, S.C.R., Parslow, D.M., Morgan,M.J., Morris, R.G., Bullmore, E.T., Baron-Cohen, S., and Gray, J.A. (2002).Functional magnetic resonance imagingof synesthesia: Activation of V4/V8 byspoken words. Nat. Neurosci. 5, 371–375.

Paulesu, E., Harrison, J., Baron-Cohen, S.,Watson, J.D.G., Goldstein, L., Heather, J.,Frackowiak, R.S.J., and Frith, C.D. (1995).The physiology of coloured hearing: APET activation study of colour-wordsynaesthesia. Brain 118, 661–676.

Robertson, L.C., and Sagiv, N. (2004).Synesthesia: Perspectives from CognitiveNeuroscience. New York: OxfordUniversity Press.

Department of Psychology, UniversityCollege London, 26 Bedford Way,London WC1 0AP, UK.E-mail: c.mulvenna@ucl.ac.uk

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Some artists' work is in response tosound–colour associations. Thispainting by British artist Mark Rowan-Hull is in response to Messiaen’scomposition Turangalîla 3.