Estudio de la actividad cortical auditiva mediante SPECT cerebral: validacion del metodo y aplicacion en la hipoacusia profunda bilateral

Abstract

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.