Understanding The Neuroscience Behind Synesthesia

Synesthesia is a neurological trait that causes some people to experience the world differently—that is, through the mixing of multiple sensory perceptions at the same time. It’s estimated to take as many as 50 or more different forms. Some synesthetes hear colors, others taste sounds, and some even associate words with smells or feel sensations when visually perceiving them in others. Synesthetic experiences have been studied since the 19th century, but only recently have scientists begun to understand some of the neurological underpinnings of this unique trait. Read on for more information about what current research says about the neuroscience behind this type of sensory experience. 

What is synesthesia?

Having synesthesia means that the stimulation of one sense is linked to perception through another. For example, someone with synesthesia might see the color blue when they hear a certain sound or smell gingerbread when they see an image of a cat. Note that synesthesia is not considered to be a medical condition or a mental illness. Instead, researchers often refer to it as a “benign” perceptual phenomenon. 

Types of synesthesia

The over 50 types of synesthesia are commonly classified into two key categories: projective and associative.

Projective synesthesia 

Projective synesthesia is characterized by involuntary, vivid, and consistent sensations in response to external stimuli. For example, a person with a type of synesthesia in this category may observe certain colors when they hear certain sounds or words. This particular form of synesthesia is often experienced as visual-auditory sensations (called chromesthesia) but can also be experienced with other senses, such as taste or smell. 

Associative synesthesia

Associative synesthesia involves involuntary mental associations between different senses that share similar features or concepts. For instance, a person with this type of synesthesia might associate the color yellow with the sound they hear when a door slams shut, even though these two stimuli are seemingly unrelated. They could also consistently perceive a connection between a particular song and the smell of freshly cut grass without any conscious effort.

Key research on the neuroscience of synesthesia

Through functional magnetic resonance imaging (fMRI) techniques, researchers have found that the visual cortex appears to be central to the synesthetic experience. Located in the posterior brain region, the visual cortex is responsible for processing sensory input from the retinas. In people with synesthetic experiences, the primary visual cortex appears more active than in others when processing sensory information, suggesting that information from other senses is being “mapped” onto the visual cortex as if it were coming from a visual stimulus. 

Other brain regions have also been identified as potentially playing roles in producing synesthetic experiences. For example, the posterior parietal cortex (PPC), located in the central region of the brain between the visual cortex and the sensory cortex, has been linked to a process known as cross-modal binding. This term refers to the information processing in the brain that occurs outside of our conscious control, which is thought to be integral to forming associations between types of stimuli. It’s been suggested as one neurological mechanism by which synesthesia may occur.

Finally, in one study, scientists analyzed past research on these neurological signs of synesthesia in an attempt to better understand them and how they relate to consciousness in general. They found a common theme across the literature: Synesthesia is associated with increased communication between various brain regions. More deeply understanding the mechanisms of how this communication works and why may one day inform researchers of different brain-behavior correlations, the core underlying processes of the mind, and the nature of consciousness itself.

Synesthesia and mental health

Some research suggests that synesthesia may actually benefit mental health and cognitive function in certain ways, depending on the type and intensity. For example, some synesthetes may potentially have:

• A greater capacity for creative problem-solving than non-synesthetes
• Increased cognitive functioning and improved memory recall 
• An increased capacity for self-awareness and self-efficacy 

It’s also worth noting research that has suggested that synesthesia could have associations with certain forms of neurodivergence and even some types of mental health challenges. Consider one study that links synesthesia traits to traits of autism, drawing parallels between the more “detail-focused attentional style and altered sensory sensitivity” of Autistic individuals to synesthetic experiences. Other research has suggested that synesthetes may be at higher risk of developing anxiety and depression, though how connected this risk may be to environment versus neurological traits is still being explored.

Seeking mental health support for synesthesia’s effects

Again, synesthesia is generally considered to be a benign trait that may even provide individuals who experience it with some benefits. That said, it’s also possible for someone with such a unique way of perceiving the world to sometimes feel lonely or isolated. They may also face the challenge of feeling overwhelmed at times by the amount of sensory input they automatically receive. In addition, it is possible for anyone to experience symptoms of a mental health condition, which may or may not be tied to the specific lived experience of someone with synesthesia. 

Regardless of the cause of any mental health challenges you may be experiencing, support is available. Forums and support groups for people with synesthesia can be found online for those who would simply like to experience greater connection with others who can understand their experiences. Meeting with a therapist can also be useful for someone who is looking for support in expressing their emotions, making sense of their experiences, learning coping mechanisms for difficult feelings or sensory challenges, and finding ways to address any symptoms of mental health conditions. 

If you’re interested in seeking therapy for challenges related to synesthesia or broader mental health, online therapy might be worth exploring. Many people with unique sensory needs find that attending sessions from the comfort of home where they can control the environment is more comfortable than meeting with a provider in person. Those who want to learn more about online therapy may consider a platform like BetterHelp. You can get matched with a licensed therapist with whom you can meet via phone, video call, and/or in-app messaging, and research suggests that this format can typically offer similar benefits to traditional in-person care. Whichever type you may prefer, support is available.