Synesthesia is defined as a neurological condition in which more than one of the bodily senses are combined. Although this phenomenon is considered to be a neurological condition, it is not listed in the ICD classifications or the DSM-IV. This is due to the fact that synesthesia does not interfere with normal daily functioning. It is considered a neurological condition to show the brain basis of such perceptual differences.
While experiencing normal sensations, other unusual sensations take place at the same time. People such as Sean Day, Matthew Blakeslee, and Jeff Coleman all experience this. For Sean Day, he sees the color blue at the same time he tastes beef and when eating food seasoned with ginger, an orange blob appears before his eyes. On the other hand, Matthew Blakeslee experiences a very vivid, bitter taste in his mouth when shaping hamburger patties with his very own hands. And Jeff Coleman sees printed black numbers in different colors, each with its own specific hue.
The temporal and parietal lobes are the main areas in the brain involved with synesthesia. When synesthesia begins, in regards to shapes and numbers, the area of the brain affected first is in the fusiform gyrus of the temporal lobes. As it progresses, the area of the brain affected next is at the TPO junction. This junction is the location where the temporal, parietal, and occipital lobes meet. As synesthesia continues, involving number and color sequences, the angular gyrus of the TPO junction is next area in the brain to be affected.
“Higher” synesthesia is driven by a numerical concept, whereas “lower” synesthesia is produced by visual appearance. For example, in the “lower” area, the visual appearance of a letter might also generate a color. As for the “higher”, it may be a sound that is generated by a letter.
Neural cross wiring is the connections between brain areas that are normally segregated. Since synesthesia seems to run in families, it is believed that cross wiring is a result of a genetic mutation. For example, the “wires” may be connected between V4 area and the number-appearance area, causing number-color synesthesia. The same would be true for the higher color area and the number-concept area. Other forms of synesthesia could also be a result from comparable cross wiring. This could very well explain why some people with synesthesia mix colors with numbers. It also may provide an answer to those who see colors when hearing musical notes.
Cross activation comes into play when the wiring was fine but there was a chemical imbalance. Brain regions that are next to each other often restrain each other’s activity. If there were to be a chemical imbalance that reduces this restraint, it would allow activity in one area to extract activity in another area close by. Theory is that if this were true, it would also occur between areas that are spread apart from each other.
One of the experiments done to better help support cross activation involved staring at a small plus sign and trying to identify the number placed off to the right. That number would then be surrounded by a different number. For example, the number 5 would then be surrounded by 3’s. The people would say that it was fuzzy but they saw a certain color and that is how they identified the number. This proved that although they were not processing the number itself, it was processing in another area of the brain, such as the fusiform gyrus. Another experiment involved people who saw days of the week as different colors. This led to the thought that there was cross wiring between the angular gyrus and the higher color area near the TPO.
Cross modal synesthesia is the combination of touch, vision and hearing pouring together to allow the building oh high-level perceptions.
An example may be the thought of a dog. A dog is known to be soft and hairy, which would be categorized as touch. Dogs also barks, which would fall into the category of sound. A dog also has a certain odor, smell, and appearance, vision. For a person with cross modal synesthesia, all of these would simultaneously occur with the sound of the word “dog” or a memory of one.
Wolfgang Khler had originally designed two drawings. One of the drawings looked similar to an inkblot. The other, looked similar to a jagged piece of shattered glass. These drawings are what would be called “bouba” and kiki”. These drawings were used as part of an experiment. People were asked to identify which drawing was “bouba” and which was “kiki”. 98% of the people in the experiment chose “bouba” to be the drawing representing the inkblot, and “kiki” as the jagged piece of glass. The reasoning behind this is due to the nature of their names. It was believed that the gentle curves of the inkblot picture metaphorically mirrored that of the pronunciation of the word “bouba” by the lips having a curved sound. “Kiki” was thought to have a harsh tone on the tongue in the palate, which would lead to the jagged piece of glass.
It is believed that synesthesia can improve memory. There was a late Russian neurologist, Aleksandr R. Luria, who had described a mnemonist who had an impeccable memory due to the fact that all five of his senses were connected. Although all of his senses were linked together, it is thought that even if two of the senses were connected, it may improve a person’s memory. If a person has more than one of the senses connected, there would be more options for them to remember an object by. For example, when a person sees a number 5, they see it in green and also taste a banana. So, that person would not only be able to remember that a number 5 is black, but also that a number 5 tastes like a banana.