With interest we read the paper by Engelhardt and coworkers on auditory cortex stimulation
via an implanted electrode overlying the posterior superior temporal lobe (i.e. secondary
auditory cortex) contralateral to lateralized tinnitus [
[1]
]. The study attempts to scientifically evaluate whether auditory cortex stimulation
has a potential to become a possible treatment option for tinnitus. The authors conclude
the technique is not efficacious in general but find some intriguing differences between
the blinded stimulation and the long-term open label outcome data. This asks for some
clarification, some of which the authors have provided: (1) placebo effect of surgery,
(2) defined target, (3) a too short randomized phase.
- 1.It is unlikely that the placebo effect can explain the clinical long-term benefit the patients perceive. A recent systematic review and meta-analysis has been shown that principally the clinical effect of placebo is rather small [2,3,4] and induces on average a 7% improvement [[2]]. The average improvement in the patient group who had a long-term follow-up (n = 5/8) was average 27.27%.
- 2.Other targets might be superior. This is based on novel data that were not available when the authors initiated their study. At that time it was conceived that the auditory cortex was the final common pathway in all tinnitus patients, but recent research suggest that the auditory cortex might be involved predominantly in patients without hearing loss, and in patients with hearing loss the parahippocampal gyrus becomes more pronounced [5,6,7,8]. Furthermore, the affective component of tinnitus is generated by a network different from the loudness network, involving the anterior cingulate cortex and medial temporal lobe, anteriorly from the amygdala extending posteriorly to the parahippocampal gyrus [9,10,11,12,13]. Further confirmation that the affective component is separable from the loudness perception can be found in frontal lobotomy data that demonstrate that the “head noises were still the same but bothered them less” [[14]]. Hence targeting the auditory cortex and evaluating using a Strukturiertes Tinnitus-Interview (STI), a measure that mainly evaluates the psychological effect of the tinnitus, is probably not ideal as you do not directly measure the loudness percept, but rather the affective component. A loudness measure using as a visual analog score or numeric rating scale might be preferred, as we know that this measure correlates with auditory cortex activity in tinnitus patients [[15]].
- 3.The short randomization phase might be another problem as it is known that after a long time of auditory cortex stimulation residual inhibition is long [[16]]. This might bias the results as patients were already stimulated for 4 months before they were randomized. It is possible that during this 4 months Hebbian plasticity could already be induced due to the constant stimulation.
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Article info
Publication history
Published online: September 25, 2014
Accepted:
September 18,
2014
Received:
July 18,
2014
Identification
Copyright
© 2014 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
