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Abstract:
It would be a mistake to assume that all healthy adults share
the same pattern of functional brain connections. In some healthy
people, functional neuroimaging, psychophysical, and self-report
data collected by ourselves and others reflect an unusual,
idiosyncratic pattern of functional connections between brain
subsystems. In this rare perceptual phenomenon (synesthesia), each
triggering stimulus automatically produces, along with the
sensation experienced by most people, a consistent concurrent
sensation not experienced by others. For example, in
colored-hearing synesthesia some sounds trigger the experience of
color. Three recent theories explain synesthetic perception in
terms of functional brain connectivity. One theory posits a role
for the limbic system. Another suggests a breakdown in modularity
between functional subsystems. A third theory suggests abnormal
disinhibition of feedbackward connections in sensory pathways.
Although many studies of synesthesia have been published, there are
insufficient physiological data to fully support any of these
ideas. We discuss how each theory addresses functional connectivity
in synesthesia, and evaluate how well each theory explains existing
data. We highlight opportunities for applying the methods of
cognitive neuroscience to better determine the neural mechanisms of
synesthetic perception, offering a way to study inter-individual
differences in functional connectivity.
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