Mirror-touch synaesthesia: the role of shared ... - UCL Discovery

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Chapter 1
(the referral of a tactile sensation away from the stimulation site; Burrack, Knoch, and
Brugger, 2006).
Synaesthetic interactions involving hearing and touch have rarely been
documented, however recently Ro et al. (2007) report a single case of acquired
auditory-tactile synaesthesia in a female patient following a discrete neurological
lesion to the right ventrolateral thalamus. The synaesthesia was first reported 18
months post lesion when the patient began to feel tactile sensations in response to
sounds. The synaesthetic somatosensations were typically experienced on the
patient’s left upper part of the body and a test of consistency (across three testing
sessions separated by 35 and 15 days) indicated that they were generally consistent
over time. Magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI)
conducted at approximately 3 years post lesion indicated disorganised fibre bundles in
the right ventrolateral thalamus (lesion site) - at 3 years post onset DTI tracking from
the unaffected left hemisphere showed direct projections to motor / premotor cortices,
whereas fibre bundles in the lesioned hemisphere were disorganised and smaller
compared to the unaffected hemisphere. DTI conducted at 1.3 years post onset (i.e.
before synaesthetic experiences were reported) indicated no white matter differences
between the right and left ventrolateral thalamus. The authors suggest that this
disorganisation in cortico-callosal pathways may account for synaesthetic experiences
(Ro et al., 2007; see Chapter 9).
In addition to cases of acquired auditory-tactile synaesthesia there are a
number of accounts of acquired synaesthesia involving vision-touch interactions.
For example, patient D.N., suffered paralysis and loss of sensation in the left side of
his body following stroke. This resulted in D.N. being unable to feel any tactile
stimulation presented to the left side when the touch was hidden from view, however