Clin Exp Otorhinolaryngol.  2023 Nov;16(4):326-333. 10.21053/ceo.2022.00423.

Increased Resting-State Positron Emission Tomography Activity After Cochlear Implantation in Adult Deafened Cats

• Park MH
• Kim JS
• Lee S
• Kim DH
• Oh SH

• KMID: 2548361
• DOI: http://doi.org/10.21053/ceo.2022.00423

Abstract

Objectives
. Cochlear implants are widely used for hearing rehabilitation in patients with profound sensorineural hearing loss. However, Cochlear implants have variable results, and central neural plasticity is considered to be a reason for this variability. We hypothesized that resting-state cortical networks play a role in conditions of profound hearing loss and are affected by cochlear implants. To investigate the resting-state neuronal networks after cochlear implantation, we acquired ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) images in experimental animals.
Methods
. Eight adult domestic cats were enrolled in this study. The hearing threshold of the animals was within the normal range, as measured by auditory evoked potential. They were divided into control (n=4) and hearing loss (n=4) groups. Hearing loss was induced by co-administration of ethacrynic acid and kanamycin. FDG-PET was performed in a normal hearing state and 4 and 11 months after the deafening procedure. Cochlear implantation was performed in the right ear, and electrical cochlear stimulation was performed for 7 months (from 4 to 11 months after the deafening procedure). PET images were compared between the two groups at the three time points.
Results
. Four months after hearing loss, the auditory cortical area’s activity decreased, and activity in the associated visual area increased. After 7 months of cochlear stimulation, the superior marginal gyrus and cingulate gyrus, which are components of the default mode network, showed hypermetabolism. The inferior colliculi showed hypometabolism.
Conclusion
. Resting-state cortical activity in the default mode network components was elevated after cochlear stimulation. This suggests that the animals’ awareness level was elevated after hearing restoration by the cochlear implantation.

Keyword

Cochlear Implants; Acquired Deafness; Positron-Emission Tomography; Auditory Cortex; Default Mode Network

Figure

• 

  Fig. 1. (A) Experimental scheme of deafening, cochlear implantation, cochlear stimulation, and positron emission tomography (PET) scans. The first PET scan was performed in a normal hearing state as a baseline measurement. The second scan was performed 4 months after hearing loss to evaluate the effect of deafness to the brain. The third scan was performed after 7 months of cochlear stimulation to evaluate the effects of cochlear stimulation. Cochlear implantation was performed during the 2nd and 3rd months after the deafening procedure. (B) Auditory brainstem response (ABR) shows a threshold of 20 dB SPL in the normal hearing state (from experimental animal no. 1). (C) After the deafening procedure, ABR shows no response to the 90 dB click sound (from experimental animal no. 1). (D) Skull anteroposterior view after cochlear implantation. At the center of the figure, introduced electrodes are identified (from cochlear implantation group no. 2). (E) Impedance measurement immediately after implantation. Eleven electrodes were introduced into the cochlea (from cochlear implantation group no. 2).

• 

  Fig. 2. (A) Both primary auditory cortical areas show decreased glucose metabolism in the hearing loss state compared with the normal hearing state. (B) The suprasplenial gyrus (visual area 17) shows increased glucose metabolism after deafness.

• 

  Fig. 3. Changes after cochlear stimulation (comparison between hearing loss [the 4th month] and after cochlear stimulation [the 11th month]). (A) Glucose metabolism decreased in both inferior colliculi after 11 months of deafness. (B) The cingulate gyrus (B1) and superior marginal gyrus (B2) show increased glucose metabolism after 7 months of stimulation.

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