All Crossed Up: Synesthesia

Synesthesia represents a rare and still somewhat mysterious functioning of the brain. It is not classified as a disorder in the formal sense because while behavior is abnormal, there is no real danger or deficiency yet associated. The result of synesthesia is a "cross-wiring" of senses, where the experience of one sense triggers another, different sense. With study of the most common form, letter-color synesthesia, researchers are beginning to understand more in connection with the brain. The future of neural imaging and brain understanding will hold more answers for this strange brain behavior.

Introduction

The brain still represents a realm of mystery and intrigue. As time passes, researchers use technology and newly acquired knowledge to bridge the gap between the mystery and understanding. And with this new understanding, new discoveries of behavior and disorder are being uncovered. This has paved the way for research into a rare brain function or "trait" known synesthesia. In the past, abnormal behavior associated with synesthesia may have been dismissed for what would seem to be insignificant impact in a person's life. Today, study of the brain has brought new life to this not so common process and allowed synesthetes to have renewed hope for understanding of their behavior. The future of bio and neuropsychology may present exciting, new information and possibilities for this seemingly strange function.

History & Background

Over 300 years ago researchers began investigating cases where people reported some form of sense confusion where one or more senses triggered others (Larner, 2006). The word synesthesia comes from the Greek "syn" meaning union and "aísthesis" meaning sensation (Day, 2007). This time period represented limited knowledge of the brain and its interaction with the body's senses. Because of this, research was ultimately left and resumed at rare intervals as time progressed. The "disorder" was not viewed as a disorder in the classical sense because there was no real negative impact on the daily functioning of the synesthete. This led to a philosophy of waiting until significant progress was made in brain functionality. . It was not until brain imaging made its introduction that synesthesia finally underwent some serious research.

In 1980, Dr. Richard Cytowic set out to discover the real neurological and physiological inner workings of synesthesia. At the time many of his colleagues maintained he would be committing career suicide. Until then, synesthesia had been classified in many different ways and there was little desire to discover its roots. Today Dr. Cytowic is credited as rediscovering synesthesia and introducing this abnormal behavior back into mainstream research. To this day he maintains a theory of synesthesia as a normal brain process that is simply only accessible to a minority of the people (http://cytowic.net/index.html). Regardless, awareness continues to grow and with the additional research and communication technology, the number of cases increases each year.

Synesthesia, an Extended Definition

So, what is exactly synesthesia? Often referred to as a blending or "cross-wiring" of senses, synesthesia represents the simultaneous stimulation of one or more senses following the stimulation of another (Day, 2007). As an example, a person may hear certain music only to have it accompanied by a specific taste. It is often incorrectly classified as a disease or disorder when in fact, it is believed to be an inherited trait associated with the X chromosome (Cytowic, 1995). This is based on the appearance of genetic heritability, supported by Dr. Richard Cytowic, but is not yet conclusive. Synesthesia is referred to as additive, meaning the secondary sensory stimulation follows the primary; it does not replace it. These stimulations can come in just about any pair of senses and in some cases can involve the triggering of multiple senses. Though there numerous forms of synesthesia, with almost each distinct possibility having at least one reported case, there are still forms that are predominate in this behavior. Generally, some association with color visualization is common among synesthetes (Acosta et. al., 2007). Below is a look at some of the various forms of synesthesia.

Synesthesia Types

Grapheme → Color synesthesia is the most common form and is reported more frequently than the rest. In this form, the synesthete sees written letters or numbers (graphemes) as being a certain colors. The non-synesthete would see these characters in black and white. This can also occur for entire words, like months of the year or days of the week (Froger & van Campen, 2003).

Music → Color synesthesia is less common than grapheme, but still one of the more common forms. In this case the synesthete experiences colors from hearing sounds and music. As an example, the playing of a piano may trigger a visualization of the color green from the synesthete.

Sight → Taste synesthesia is far rarer and represents the possibility of almost any two senses to blend. With this type, the synesthete will respond to pictures of objects by experiencing an associated taste (Than, 2006).

There remains some debate on the frequency with which synesthesia occurs in the general population. This is based on its only recent introduction to mainstream research as well as some mildly varying definitions. Most figures put the occurrence of this behavior at 1 in 25,000, making it fairly rare (http://www.macalester.edu/psychology/whathap/UBNRP/synesthesia /main.html). However, this number will vary according to the type involved and level of intensity. Some of the most basic forms of cognitive synesthesia (e.g. colored letters) estimate around 1 in 500, making it much more common (Day, 2007). Additionally, some common trends exist for cases of synesthesia. This behavior is more frequent in people who are left-handed. It is also more common in women (Phillips, n.d.). These factors all relate to genetic implications that are waiting to be uncovered. Ultimately, it will be the understanding of synesthesia's relationship to the brain that will paint the clearest picture.

Synesthesia and the Brain

As discussed previously, synesthesia is based on our brain's perception of our senses. Understanding this process has been the key to researchers understanding this behavior and exactly what the brain is doing. So what is going on inside the synesthete's brain that differs from normal brain processes? The synesthetic experience is dependant only on the left brain and is associated with a decreased blood supply to the neocortex. The resulting limbic expression indicates an association or influence primarily from the limbic system (Phillips, n.d.). Figures 1 & 2 depict the limbic system, which is involved in the processing of this sensory data.

Figure 1 - The structures in the Limbic System Figure 2 - 3d model of the Limbic System

As the brain plays a critical role in sensation, it is natural for researchers to look to it to learn more about synesthesia. The diagnosis of this trait or behavior is no simple matter. The difficulty comes from the fact that synesthetic properties or symptoms are not really recognizable from the outside. This means the science must rely on the individual to come forth and report a case.

Diagnosis

Once an individual reports the possibility of synesthesia, diagnosis can generally be accomplished through two methods:

§ Tests/Questionnaires

§ Analysis of neural imaging

Often, these techniques work best when used in conjunction with each other. The focus will remain on neural imaging techniques as they show the most technical promise for learning more in the future. There are numerous online resources for test and questionnaires that can help a potential synesthete diagnose their behavior. One such resource, www.synthesthete.org, provides a battery of tests for this information.

The most promising form of diagnosis and research is being accomplished through the various available neural imaging techniques. Both functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET) Scan technology have offered some further insight. The detail of the fMRI has really helped identify the varying responses in the brain of a synesthete. Below are examples these neural imaging techniques used to compare brain behavior in synesthetes and non-synesthetes.

Example 1 - fMRI

http://ucsdnews.ucsd.edu/newsrel/soc/SynestheticColors.asp

In the above image, subjects were shown (visually), black and white letters. The pink area represents the color-selective region of the cortex. The red represents brain activity. This clearly shows brain activity in the synesthete in the area of color-selectivity. The control responds without such brain activity as the subject sees only black and white (Kidera, 2005). This image represents the great power of new fMRI technology. While this was used to demonstrate the common grapheme → color synesthesia, the application not limited to such. Other senses can be stimulated to view the varying results.

PET scan (see next page)

Example 2 - PET scan

(Paulesu, et. al., 1995)

The above image once again represents grapheme → color synesthetes (top) and non-synesthetes (bottom). The purpose of a PET scan is to detect differences in the metabolic activity of the tissues. Here, there are clear indications of differing activity from the top to bottom. The yellow intensity changes location in the synesthete vs. non-synesthete (Paulesu, et. al., 1995).

(Diagnosis cont'd)

While it may seem like the above images only confirm activity that the person claims, they represent an important step in understanding the relationship to the brain. Pinpointing areas of the brain that contribute to behavior can help lead to all kinds of future discoveries. And while this particular trait may not be something that requires "treatment" in the traditional sense, there are still many people searching for answers. Neural imaging techniques have opened paths to begin answering these questions.

Treatment

Simply put, synesthesia is not something that will be treatable any time soon. This has more to do with the fact that treatment is generally unnecessary and undesirable for harmless genetic traits. It is important to mention again that this is not a disorder; it is a trait, much like having red hair. There are rare circumstances where the effects of this behavior may induce pretty severe and inconvenient incidents. For example, a person may have forms of synesthesia that produce negative sensory reactions like foul tastes, unpleasant touch response (pain), or even visual cues that impede a normal daily operation (Choi, 2007). These could present scenarios that demand treatment, but until they are a more common occurrence, they will not be a priority. For now the best treatment available is information and the ability to cope with this odd brain function.

The Life of a Synesthete

There are both advantages and disadvantages to being born with such a trait. Fortunately for most with synesthesia, the benefits outweigh the inconveniences and annoyance. The average synesthete experiences some sort of visual accompaniment to another sense. This is not always the case, as any pairing of senses is possible, but it is part of an overwhelming number of cases. On the outside, this experience may seem like an annoyance, but in fact it is very beneficial to most people. People diagnosed with synesthesia generally perform at a higher proficiency in memory related tasks (Cytowic, 1995). This is because the visual characteristic creates and additional tool for memory. According to one of the fathers of modern synesthesia research, synesthesia is advantageous trait that all humans have, but only a small have been able to unlock. Most synesthetes learn to expect and use their different sensory experiences to their advantage. It is only the rare cases, as was first mentioned in the treatment section, that lead to unfortunate circumstances. It is possible for the sense experience to interfere, though usually mildly, with daily functioning. One man responded to certain sounds/music with colors in his visual field (Day, 2007). This could present a distraction if the person was driving. Even with the potential, small annoyances, most synesthetes are able learn to cope over time. Because of this, a day in the life of a synesthete is much like anyone else.

Conclusion

Each day brings us closer to the technology that will provide understanding to all the questions the brains and its functions create. Synesthesia represents one more mystery that is beginning to make its way from the shadows and into the light. A synesthete is not something you can pick out of a crowd; their lives unfold much the same way as everyone else. Is it the future evolution for the majority of humans or is it simply a rare abnormality for the minority? Only time and understanding will reveal the answer. In the mean time, researchers must continue plodding away to uncover all of what the brain has to teach us. Hopefully, synesthetes and non-synesthetes alike will discover the answers to all of their questions.

References

Acosta, A., Callejas, A., & Lupianez, J. (2007). Green love is ugly: Emotions elicited by

synesthetic grapheme-color perceptions. Brain Research, 1127(1), 99-107. Retrieved October 17, 2007 from PsychInfo database.

Association for Psychological Science. (2007). Synesthesia: Common Letters And

Numbers Are Brighter, Study Suggests. Science Daily. Retrieved October 23, 2007 from http://www.sciencedaily.com­ /releases/2007/09/070918161553.htm

Boeree C.G. (2002). The Emotional Nervous System. Retrieved October 18, 2007 from

http://webspace.ship.edu/cgboer/limbicsystem.html

Carpenter S. (2001). Everyday fantasia: The world of synesthesia. Retrieved October

15, 2007 from http://www.apa.org/monitor/mar01/synesthesia.html

Cytowic, R. (1995). Synesthesia: Phenomenology And Neuropsychology. Retrieved October

23, 2007 from http://psyche.cs.monash.edu.au/v2/psyche-2-10-cytowic.html

Day, S. (2007. Definition of "synesthesia". Retrieved October 15, 2007 from

http://home.comcast.net/~sean.day/html/definition.html

Choi, C.Q. (2007). Study: People Literally Feel Pain of Others. Retrieved October 17, 2007 from http://www.livescience.com/health/070617_touching_faces.html

Froger, C. & van Campen, C. (2003). Personal Profiles of Color Synesthesia. Retrieved

October 17, 2007 from http://www.synesthesie.nl/pub/personal%20profiles.htm

Kidera, I. (2005). Neuroscientists Locate 'Imaginary' Colors. Retrieved October 15,

2007 from http://ucsdnews.ucsd.edu/newsrel/soc/SynestheticColors.asp

Larner, A.J. (2006). A Possible Account of Synaesthesia Dating from the Seventeenth Century.

Journal of the History of the Neurosciences, 15(3), 245-249. Retrieved October 23, 2007 from PsychInfo database.

Paulesu, E., Harrison, J., Baron-Cohen, S., and Watson J.D.G. (1995). The physiology of

coloured hearing: A PET activation study of colour-word synesthesia. Brain 118, 661-676. Retrieved October 17, 2007 from PsychInfo database.

Phillips, M.L. (n.d.). Neuroscience for Kids - Synesthesia. Retrieved October 15, 2007

from http://faculty.washington.edu/chudler/syne.html

Than, K. (2006). New Insight into People Who Taste Words. Retrieved October 17,

2007 from http://www.livescience.com/health/061122_word_tastes.html

Website(s)

http://cytowic.net/index.html

http://home.comcast.net/~sean.day/Synesthesia.htm

http://www.macalester.edu/psychology/whathap/UBNRP/synesthesia/main.html

http://synesthesia.info/