Functional studies (neuroSPECT) of the human auditory pathway

Objectives To determine cortical and basal ganglia response to auditory stimuli with HMPAO cerebral perfusion studies and to evaluate the consistency of the method to evaluate the auditory pathway.

Methods Comparison of 31 brain perfusion SPECT studies done in normal hearing volunteers with monaural (10) and binaural (6) pure tone stimulation, normal hearing musicians while evoking music (3) and to two patients with auditory hallucinations after abrupt hearing loss. All subjects had 99mTc-HMPAO injected in a sound proof, dimmed light room either while being stimulated with pure tones, evoking or hallucinating. SPECT imaging was done 1 hour later. Comparison to a normal non-stimulated database was done using the Oasis software (Segami Corp., USA).

Results Subjects had >2 standard deviations (SD) bilateral cortical hyperperfusion in Brodmann’s areas 9 and 10,parietal areas 39 and 40 (Wernicke) and markedly in both thalami, interpreted as activation. There was consistently hypoperfusion in areas 38 (temporal pole) considered as inhibition. Pure tone stimulation, monaural and binaural, showed additional bilateral cortical activation (>3SD) in Brodmann's areas 7 (somatosensory association cortex), 17, 18 and 19 (associative visual cortex), 23, 31, 32, in temporal areas 21, 22 (auditory association areas). Response to binaural stimulation was less intense in areas 19, 21 and 22 compared to monaural stimulation; hallucination had no activation of areas 21 and 22.

Conclusions Multiple areas involved and simultaneous participation of activated/deactivated cortical regions suggests that the auditory pathway is complex and involves a number of modulation and association relays that process the auditory information. This occurrence should determine not only what reaches the cortex but also where in the cortex a specific stimulus will be processed. The reproducibility of the results for monaural and binaural stimulation with pure tones in the same 6 subjects confirms the consistency of the testing method.

Research Support Institutional Grant,Clïnica Las Conde