Cortical activation in pre-lingually deaf adults, with and without a cochlear implant

A cochlear implant (CI) is a implantable electronic device that provides
hearing sensations to patients with profound or total sensorineural hearing
loss. Most of the children and postlingually deafened adults have favourable
outcomes after implantation, however the benefits provided by CI*s display a
great variability in adults who lost their hearing ability before the
development of speech and language, the so-called *pre-lingually deaf*
candidates. The prediction of substantial communication benefits after cochlear
implantation is still a clinical dilemma. Until now, no objective tests have
been described to predict the outcome of implantation in this pre-lingual
patient group. Previous studies suggest that probably PET could be used to
assess glucose-metabolism in the auditory cortex pre-operatively in order to
predict postimplantation CI results.

In order to asses the hearing performance after cochlear implantation in an
objective way, *Event Related Potentials* (ERPs) can be used to study auditory
neural processing on a cortical level using conventional EEG techniques.

A relation is expected between hearing performance in implanted (pre-lingually)
deaf patients on the one hand and cortical metabolism and electrical activity
on the other.

The primary objective of the present study is to increase our insight in the
neural processing of speech in pre-lingually deaf CI patients regarding the
prediction and explanation of postoperative differences in performance within
this specific group of cochlear implant users. To that end we will investigate:
a. the differences in performance of pre-lingually deaf patients with a
cochlear implant (study A).
b. the differences in cortical activity between normal hearing and implanted
pre-lingually deaf patients (study A).
c. the predictive value of brain metabolism, measured by PET scanning, on
postoperative behavioural and objective electrophysiological responses in
pre-lingually deaf patients (study B).
d. the cross-modal plasticity before and short and long term after implantation
(study B).

Two observational studies:

Study A
In order to investigate the differences between between good and poor
performers with CI and to relate these results to normal hearing subjects,
three groups will be investigated: five pre-lingually deaf implanted patients
with a good result, five pre-lingually deaf implanted patients with a poor
result, five normal hearing healthy volunteers. Each subject participates in 3
PET studies (1 scan without stimulation, 1 scan with auditory stimulation and 1
scan with visual stimulation) and 1 ERP measurement.


Study B
In order to investigate the predictive value of brain metabolism and to
investigate the cross-modal plasticity before and short and long term after
implantation 13 pre-lingually deaf candidates for cochlear implantation will be
evaluated one month before surgery, half a year after implantation and two
years after implantation.
One months before surgery they will participate in 2 PET-studies (1 scan
without stimulation, and 1 scan with visual stimulation). Half a year and 2
years after surgery they will participate in 3 PET studies (1 scan without
stimulation, 1 scan with auditory stimulation and 1 scan with visual
stimulation) and 1 ERP measurement.

Study A:

Subject will participate in three 120 MBq [18F]-FDG PET-CT studies. The
radiation load in this study is 7.4 mSv in two weeks ( 3 times an intravenous
injection of 120 MBq [18F]-FDG PET corresponds with 6.8 mSv plus 3 times
CT-scan corresponds with 0.6 mSV). All scans will be performed on 3 different
days within two weeks. Before one of the three scans the subjects participate
in the ERP experiment. No adverse events or risks are suspected.

Study B:

The radiation load in this study is 19.8 mSv in 2 years (8 times an intravenous
injection of 120 MBq [18F]-FDG corresponds with 18.2 mSv in 2 years plus 8
times CT-scan corresponds with 1.6 mSV).
The preoperative scans are performed 1 month before surgery, on 2 different
days, within one week.
The postoperative scans are performed on 3 different days, spread over 2 weeks.
Before one of the three postoperative scans the subjects participate in the ERP
experiment. These postoperative investigations are performed half a year and
two years after implantation. No adverse events or risks are suspected.