Changes in activation of the auditory cortex following long-term amplification: an fMRI study

Speech-elicited activation decreased after monaural amplification bilaterally during unaided or aided ear stimulation, but tended to recover later at the contralateral hemisphere during aided ear stimulation.

The purpose of this study was to investigate the changes in the activation pattern of auditory cortex following long-term monoaural amplification.

Serial functional magnetic resonance images were obtained while speech sounds were presented to the aided (right) and unaided (left) ears of eight hearing-impaired subjects before, 3 months, and 9 months after beginning the use of a single hearing aid. The results were analyzed by group analysis.

Before hearing aid fitting, we found that activation patterns of the auditory cortex were somewhat segmented in the left hemisphere, regardless of whether the speech sounds were delivered to right or left ear. Cross projection was lost in response to right ear stimulation. After hearing aid fitting, on the unaided side stimulation, the activation tended to decrease progressively on both sides 3 months and 9 months after beginning monoaural amplification. On the aided side stimulation, activation also decreased 3 months after amplification bilaterally, but tended to recover at the contralateral hemisphere after 9 months of amplification. Cross projection was restored in response to right ear stimulation.