Color synesthesia. Insight into perception, emotion, and consciousness

Abstract

Purpose of reviewSynesthesia is an extraordinary perceptual phenomenon, in which individuals experience unusual percepts elicited by the activation of an unrelated sensory modality or by a cognitive process. Emotional reactions are commonly associated. The condition prompted philosophical debates on the nature of perception and impacted the course of art history. It recently generated a considerable interest among neuroscientists, but its clinical significance apparently remains underevaluated. This review focuses on the recent studies regarding variants of color synesthesia, the commonest form of the condition.Recent findingsSynesthesia is commonly classified as developmental and acquired. Developmental forms predispose to changes in primary sensory processing and cognitive functions, usually with better performances in certain aspects and worse in others, and to heightened creativity. Acquired forms of synesthesia commonly arise from drug ingestion or neurological disorders, including thalamic lesions and sensory deprivation (e.g., blindness). Cerebral exploration using structural and functional imaging has demonstrated distinct patterns in cortical activation and brain connectivity for controls and synesthetes. Artworks of affected painters are most illustrative of the nature of synesthetic experiences.SummaryResults of the recent investigations on synesthesia offered a remarkable insight into the mechanisms of perception, emotion and consciousness, and deserve attention both from neuroscientists and from clinicians.

Anatomy and white matter connections of the fusiform gyrus

“…The fusiform gyrus has also been implicated in grapheme-color and tone-color synesthesia, in which the left posterior fusiform gyrus has been found to have increased gray matter volume, while the left anterior fusiform gyrus, as well as the left MT/V5, have decreased gray matter volume 38 . Finally, there is evidence that the fusiform gyrus demonstrates selectivity for human bodies, separate from faces or tools 6 .…”

A Lesion-Proof Brain? Multidimensional Sensorimotor, Cognitive, and Socio-Affective Preservation Despite Extensive Damage in a Stroke Patient

“…Yet, after clinical stabilization, the patient presented neither additional neurological deficits nor cognitive, emotional or behavioral impairments. The only immediate changes she reported were loss of sensitivity on the right hand and a transient form of personality-color synesthesia (Ramachandran et al, 2012; Safran and Sanda, 2015). She was soon discharged to her home, under supervision of a caregiver, and started physical therapy sessions.…”

The Neurophenomenology of Out-of-Body Experiences Induced by Hypnotic Suggestions

“…On the other hand, H-OBE depend on an introspective activity intentionally performed by the subject, a fact hardly compatible with the idea of neurological dysfunction. Likewise, synesthesias were considered in the past decades as a deficit of separation of perceptual modalities due to a developmental failure, brain lesions or the use of hallucinogens; instead, they may depend on a higher-than-normal brain connectivity related to better-than-normal activity, such as creativity (Chun & Hupe, 2016;Grossenbacher & Lovelace, 2001;Mroczko-Wasowicz & Werning, 2012;Safran & Sanda, 2015).…”