Synesthesia

A Review of the Research on Synesthesia Imagine hearing a color, tasting a shape, or even feeling a sound. Many people actually experience this because they have been diagnosed with a condition called synesthesia. Synesthesia is when the stimulation of one sense produces the sensation of another sense. Synesthesia was most likely first mentioned in 1812 in a medical report written by German physician Georg Tobias Ludwig Sachs. Research on this condition flourished in the 1980s, and since then synesthesia has been researched by many scientists. The results of their work are the many facts that have been revealed about this sense combining condition.

Characteristics of Synesthesia Synesthesia, which means joined perception, comes from

Some researchers say that synesthesia occurs because of an overabundance of neural connections in the brain, causing neurons and synapses from one sensory system to cross into another. This allows single sense areas to receive feedback from multisensory areas. The Neonatal Theory explains that all people are born with these overabundant neural connections, but, as they mature, certain connections are strengthened and unused connections are pruned away. Synesthetes are believed to have retained these extra neural connections which enable a sort of cross-wiring in the brain. This theory is supported by the results of Diffusion Tensor Imaging. A DTI measures the amount of water flowing in the brain because in certain nerve fibers, water flows more freely in one direction than the other. By measuring the water flow, scientists can determine how many axons are in each brain region. The axons that connect different parts of the brain are called “white matter” or “white matter axons.” Brain regions that have more white matter axons are more strongly connected. In the brains of synesthetes, scientists have found high levels of white matter, especially in the V4 color recognition

The most common form of synesthesia is called grapheme-color. Grapheme-color synesthesia is where individual letters or numbers have colors associated with them (“Types of Synesthesia”). The letters or numbers can appear colored on the page or visualized as having the color in the mind. Grapheme-color synesthesia belongs to a specific category called ideasthesia, which is when a concept co-activates a sensory experience (“Grapheme Color Synesthesia”). Many synesthetes report that the color associated with a letter or number is different, but consistent, for every digit. It has been found that the synesthete must be attentive and focusing on the letter or number in order to perceive the experience. The actual sensation occurs when the grapheme recognition area is activated which co-activates the visual cortex to produce a color (“Grapheme Color