Synaesthesia and the Brain  Synaesthesia is a complex experience
and, being rare, it is difficult to study. Nevertheless, several
interesting theories have been proposed and tested. The idea
that synaesthesia is a mental illness is long gone, but that
doesn't mean it's not "all in the head"! Positron Emission
Tomography (PET) scans have shown that different areas of the
brain are active for synaesthetes experiencing a cross-modal
association than for non-synesthetes engaged in the same task.
The synaesthetic experience depends exclusively on the left
brain and is associated with a decreased blood supply to the
neocortex. This results in enhanced limbic expression.
Therefore, we can assume that the system responsible for
synaesthesia is located or influenced by the limbic system more
than the neocortex, which is not what most people would predict
without the evidence from the PET scans. Additional support for
this is that there is an emotional aspect associated with a
synesthetic experience. In fact, in order