| Summary: | To evaluate the differences in the functional activity of the auditory cortex
between normal hearing and profound deafness, a perfusion single photon emission
tomography (SPECT) study was designed. SPECT stereotaxic localisation of the
auditory cortex was previously validated in 2 brains by means of an anatomical
study of the macroscopic localisation and cytoarchitecture of the auditory
cortex. Additionally, 15 controls with normal hearing and 30 patients with
profound bilateral deafness were scanned using external anatomical point sources
(glabela, ineon) for stereotaxic location of the auditory cortex. The normal
controls were scanned in auditive deprivation and, in 10 cases, during a
monoaural tonal stimulation. Cerebral blood flow relative to cerebellum (relCBF)
was assessed in the auditory cortex. The anatomical study showed that mean
differences between the true auditory cortex size and the measured SPECT value
were less than 2.5 mm. Nevertheless, only the caudal aspect of this area
corresponded to the primary auditory cortex in the cytoarchitectonic study.
During tonal stimulation, control subjects presented a significant increase of
relCBF in the auditory cortex bilaterally, with significant differences in the
asymmetry index (contralateral to the side of stimulation). The relCBF in the
auditory cortex of controls in deprivation conditions was significantly higher
than in deaf patients. There were no significant differences between groups of
deaf patients, however the highest values were seen after cochlear implant. SPECT
is a suitable method for studying changes in auditory cortex activity relative to
different functional conditions, with a possible role in cochlear implant
candidates in predicting the future benefit of the implantation.
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