Anomalous Auditory Cortex Activations in Colored Hearing Synaesthetes: An fMRI-Study

Area of Science:

• Neuroscience
• Cognitive Psychology
• Sensory Perception

Background:

• Synaesthesia involves experiencing one sense through another, like hearing colors.
• Previous research linked synaesthesia to visual cortex activation but lacked mechanistic explanation.
• The neural basis of cross-modal activation in synaesthesia remains unclear.

Purpose of the Study:

• To investigate the neural mechanisms underlying cross-modal activation in color-hearing synaesthesia.
• To compare brain activity in synaesthetes and non-synaesthetes using auditory and verbal stimuli.
• To test the disinhibited feedback hypothesis as a potential explanation for synaesthesia.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to measure brain activity.
• Synaesthetes were exposed to words and tones, reporting associated color perceptions.
• Brain activations were compared between synaesthetes and controls under identical stimulus conditions.

Main Results:

• Both words and tones elicited abnormally high activation in visual and auditory cortical areas in synaesthetes, even when color percepts were infrequent.
• Synaesthetes showed significantly greater activation in visual areas (occipital lobe, fusiform gyrus) and auditory areas (superior temporal gyrus) compared to controls.
• Auditory areas in synaesthetes exhibited similar activation levels for both words and tones, unlike in controls.

Conclusions:

• The findings support the disinhibited feedback hypothesis as the neurophysiological basis of synaesthesia.
• Abnormal cross-modal activation, even without consistent percepts, highlights altered neural connectivity in synaesthetes.
• This study provides evidence for a shared neural mechanism for synaesthetic experiences triggered by different sensory inputs.