Introduction:
On the long term it is desirable for CI users to control their device in a closed
loop via brain signals. A promising approach is the use of auditory evoked potentials
(AEP) and several studies have shown the possible suitability of auditory paradigms.
However, these investigations are based on non-invasive signal acquisition which requires
the use of additional EEG electrodes mounted on the users scalp. For CI users in an
everyday life application it is more convenient to use implanted electrodes for recording
the signals. Further it is to be expected that invasively recorded signals are of
higher quality and are less affected by artefacts.
Method:
In this project we investigate the feasibility of implanting epidural electrodes temporally
during the CI surgery and the possibility to record AEPs in the course of several
days. Intraoperatively E-ABR and E-MLR are recorded, postoperatively different kinds
of AEP (ABR, MLR, CERA, MMN, P300). After a few days the epidural electrodes are removed.
Results:
First data sets of ten patients were obtained which show promising results. The recorded
potentials were compared to the clinical standard recordings using adhesive electrodes.
The quality measure based on standard error showed a significant better signal quality
for the epidural recordings. Especially cortical evoked response audiometry (CERA)
depicted clearer N100 waves which were also visible at lower stimulation intensities.
Furthermore the signal was less disturbed by artefacts.
Conclusion:
Altogether the approach is feasible, safe and well tolerated by the patients. Signal
quality of the epidural recordings is better than with adhesive electrodes and the
AEP waves are clearly recognizable. Future CI systems should include according measurement
electrodes.
