Sensory Overload or Synesthesia?

Modern life in the twenty-first century might be defined by the state of sensory overload.  Cell phones and iPods, Blackberrys and computer screens, fast food and designer perfume put our ears, eyes, nose, tongue and skin into overdrive.  What saves us from falling into a tangled web of sensory data might lie in our ability to classify these sensations into distinct categories.  In other words, I might be listening to Fergie while eating a peach while watching Entourage while scratching my leg, but I am comforted by the cognitive awareness that each sensation, although simultaneous, is separate.  Then what of the synesthete, those rare individuals who experience the neurological phenomenon of two or more sensory perceptions from a single stimulus <a href="/exchange/#1">(1)</a>?  Is their condition of synesthesia a burden or an inspiration in this world of overwhelming sensory stimulation? 

    Scientists first documented synesthesia in the 1880’s, when Francis Galton observed that certain otherwise physically normal people experienced specific colors upon hearing specific sounds or seeing specific numbers <a href="/exchange/#2">(2)</a>. Interest in synesthesia then waned as research in psychology focused on behavior rather than cognition, but synesthesia has recently reemerged as both a legitimate and exciting topic of research linking neuroscience, psychology and genetics <a href="/exchange/#3">(3)</a>.  A pioneer in the modern study of synesthesia is Richard  Cytowic, whose research in the 1980’s proposed that synesthetes experience this condition involuntarily, project the experience beyond “the mind’s eye”, maintain their intersensory experiences consistently throughout their lives and are more common in women and non-righthanded individuals <a href="/exchange/#1">(1)</a>.  Cytowic links the cause of synesthesia to a decrease in blood flow and oxygen delivery within the left hemisphere of the neocortex <a href="/exchange/#1">(1)</a>. Also during the 1980’s, Simon Baron-Cohen and his colleagues at Cambridge University proposed that Neonatal Synesthesia (NS), a condition in which humans up to four months in age experience sensory input without differentiating the source of stimulation, is a normal phase of human development.  According to Baron-Cohen, adult synesthesia results from neurological abnormalities that do not reduce the sensory connections of the neonate stage <a href="/exchange/#4">(4)</a>. Indeed, this neurological “abnormality” is estimated to occur in 1 out of 200 people and can manifest in over 100 different types of synesthesia.  Nevertheless, synesthesia is typically an additive sensory condition experienced in one direction: while a synesthete might always perceive the number seven as yellow, the color yellow will not trigger the perception of the number seven <a href="/exchange/#5">(5)</a>.

Among the most exciting recent research on synesthesia have been conducted by Vilayanur Ramachandran and Edward Hubbard of the Center for Brain and Cognition at the University of California at San Diego, who have contributed new neurological evidence to explain the synesthetic experience.  Their research provides further insights into the evolution of thought, language, and human consciousness, and their approach sheds light on the neurological process of cross-modal perception in separate areas of the brain <a href="/exchange/#3">(3)</a>.  They have explored two possible causes: 1) the tendency of bordering brain regions to inhibit mutual activity: when a chemical imbalance blocks the inhibitory neurotransmitter or fails to produce an inhibitor, cross-linking occurs; 2) a genetic component mutates connections between typically segregated brain areas <a href="/exchange/#3">(3)</a>.

 Ramachandran and Hubbard have used the technology of Functional Magnetic Resonance Imaging (FMRI) to compare the brain activity of synesthetes with those of normal perception.  Their lab has traced neural signals traveling by optic radiation from the retina to the area of the brain labeled “17”, an area in the occipital lobe linked to the perception of color, form, motion, and depth.  From “17”, the neural signals travel to an area labeled “V4”, which they propose is the site for cross-linking between color and numbers.  They demonstrate that this “V4” area was highly active in synesthete subjects that perceived white colored numbers against gray backgrounds, while remaining inactive in subjects with normal perception.  They hypothesize that the perception of colors travel to a “higher” area near the junction of the temporal, parietal and occipital (TPO) lobes that is similar to the neurological site of numerical computation <a href="/exchange/#3">(3)</a>.  However, Ramachandran and Hubbard also argue that there are synesthetic subjects that associate certain colors with the visual appearance of the number rather than with the mathematical concept of that number.  That is, these synesthetic subjects did not perceive colors when Roman numeral equivalents were substituted for Arabic numerals that typically triggered colors.  These findings suggest that grapheme-color synesthesia occurs within the fusiform gyrus that is involved with analyzing visual forms rather than abstract concepts.  Yet for synesthetes, in which the abstract concept of numbers triggers colors, the cross-linking occurs between the angular gyrus near the TPO lobes. 

This brief summary of recent research on synesthesia demonstrates that our knowledge of this condition is constantly expanding, and the only safe conclusion that can be made at this time is that gene mutation causes the ever-expanding variations of synesthetic experience.  However, the connection between synesthesia and genetics raise several important questions for future research.  Which gene is linked to synesthesia?  Can synesthesia be cultivated?  And can synesthesia shed light on the profound questions of human experience related to consciousness, language and abstraction?  “Given the right questions, the right experiments and the right patients, the study of synesthesia might illuminate the very questions that have remained in the domain of philosophers” <a href="/exchange/#6">(6)</a>.

Web Resources

1. <a name="1"> )</a><a href=" http://psyche.csse.monash.edu.au/v2/psyche-2-10-cytowic.html ">; </a>; Synesthesia: Phenomenology and Neuropsychology, A Review of Current Knowledge</a>

2. <a name="2"> )</a><a href=" http://www.bbc.co.uk/radio4/reith2003/lecture4.shtml ">; </a>; BBC Reith Lectures 2003, The Emerging Mind</a>

3. <a name="3"> )</a><a href=" http://psy.ucsd.edu/chip/pdf/SciAm_2003.pdf ">; </a>; Scientific American, May 2003</a>

4. <a name="4"> )</a><a href=" http://psyche.csse.monash.edu.au/v2/psyche-2-10-cytowic.html ">; </a>

5. <a name="5"> )</a><a href=" http://psyche.csse.monash.edu.au/v2/psyche-2-27-baron_cohen.html ">; </a>; Is There a Normal Phase of Development, Departments of Experimental Psychology and Psychiatry at The University of Cambridge</a>

6. <a name="6"> )</a><a href=" http://www.neurologyreviews.com/jul02/nr_jul02_mindseye.html ">; </a>;; The Neurology Reviews</a>