Cross-modal plasticity in the auditory cortex of pre- and postlingual deaf patients

In two proposed experiments we investigate neural and cognitive changes that
are caused by deafness. First, we will perform an fMRI experiment to study the
neural activation in response to visual cues in adults that became deaf in
early childhood (prelingually deaf), adults that became deaf at a later age
(postlingually deaf) and hearing controls. Previous studies found activity in
the auditory brain regions of deafened subjects in response to visual
stimulation (Finney et al., 2001; Sadato et al., 2004). This indicates that
when the auditory cortex is deprived from its original input a functional
neuronal reorganization can occur, such that the auditory cortex is sensitive
to new sensory modalities like vision. This capacity to reorganize and respond
to new modalities is called cross-modal plasticity. In cochlear implant (CI)
users, whose hearing is partially restored by the implant, cross-modal
plasticity can negatively influence speech perception, especially in
prelingually deaf patients (Kral & Sharma, 2012). In this fMRI experiment we
will investigate which neural regions become active when subjects look at
visual stimuli. Since cross-modal reorganization is thought to take place
mainly between the age of 3.5 and 7 years (Kral & Sharma, 2012), we expect that
the amount of visually evoked activation in the auditory cortex is highest in
the prelingually deaf, lower in the postlingually deaf and almost absent in the
hearing controls.
Second, we will perform a spatial and temporal memory experiment in which
participants have to relocate objects on a computer screen, to examine the
effects of cross-modal plasticity at the cognitive level. Deafened persons rely
more on the visual sense than hearing persons (Arnold & Murray, 1998), and are
therefore hypothesized to perform better at spatial tasks. However, for the
temporal tasks we expect the deafened persons to perform worse than the hearing
controls, as hearing is essentially based on temporal processing, and thereby
temporal processing skills may at least partially depend on the auditory system
(Conway & Christiansen, 2005; Conway et al., 2009). The postlingually deaf are
expected to perform between prelingually deaf and normal hearing.
By comparing the neural and cognitive data we will examine to what extent
cognitive outcomes are related to the amount of reorganization of the brain.
This study might therefore contribute to a better understanding of the
plasticity of the auditory cortex after deafness, which might contribute to
refinement of therapy with use of CIs, specifically for the prelingually deaf
CI users.

The main objective of the fMRI experiment is to examine differences in the
amount of visually evoked activation of the auditory cortex between hearing and
deafened adults and between pre- and postlingually deafened adults.

The main objective of the memory experiment is to examine performance
differences in spatial and temporal memory tasks between hearing and deafened
adults and between pre- and postlingual deafened adults.

This is an observational study performed at the University Medical Center (UMC)
Utrecht, consisting of two experiments.
In the fMRI experiment, functional images of brain activity will be generated
with a 7 Tesla MRI scanner. Deafened and hearing subjects will participate in a
visual experiment, in which visual stimuli are presented during acquisition of
the fMRI scans. Hearing control subjects also participate in an auditory
experiment, in which acoustic tones are presented, in order to localize the
auditory cortex.
In the memory experiment the same subjects that participated in the fMRI
experiment will, after a short memorization phase, relocate objects on a
computer screen in a specific spatial or temporal order. The memory experiment
will be performed twice on two separate days in order to test reliability.

The total duration of the study is three hours, including the time that is
needed for explaining and training the tasks. The total time in the 7 Tesla MRI
scanner for the subject will be approximately 40 minutes. While in the scanner,
participants can experience a temporary feeling of dizziness, taste of metal
and hot and cold feelings. The narrow scanner can also cause claustrophobic
feelings. However, there are no known risks involved in fMRI acquisition.
The memory experiment will be performed on a computer, basically like a
computer game, so the possible risk is negligible. Next to financial
compensation, participation in the experiment will offer no direct advantage
for individual subjects.
No immediate benefits for individual subjects are to be expected from
participation in this study. However, the knowledge on cross-modal plasticity
derived from this study might contribute to the improvement of the hearing
capacity of both prelingual and postlingual CI-users, through refinement of
therapy with the cochlear implants.