The human brain is regarded as an ensemble of dynamic systems. Communication between neural centres is of the utmost importance and many different cortical and subcortical brain areas have to coordinate to perceive sounds. The proper connections between brain areas are essential for normal hearing. After hearing loss, the connections and information pathways between these areas rearrange and this may be one of the major reasons for unsatisfactory speech perception after cochlear implantation. The brain may re-organise or even have/make plasticity for better speech perception after cochlear implantation but the success of this process depends on many factors such as the age of implantation and the length of deafness. It is shown that although both children and adults can benefit from cochlear implantation, for adults it is not as much as children. It remains unclear how the brain connection/ re-organisation contributes to these situations.
The brain organisation can be quantified by connectivity measures, which may provide the strength, direction, and timing information on the connection between brain areas. One approach to measure brain connectivity is Dynamic Causal Modelling (DCM). DCM is a biophysically informed model which models the strength of couplings between two areas and the effect of one area over itself based on a neural mass model adapted from the Jansen neuronal model. DCM assumes that a designed input is perturbing the model and its output is measured as the brain response recorded in surface EEG, MEG or fMRI. The parameters of the model include inter- and intra-area coupling coefficients, conduction delays, and input parameters and are estimated employing a Bayesian framework.
This research project aims to investigate the effective brain connectivity in normal people and patients with unilateral and bilateral cochlear implants using surface EEG during tone, word and sentence perception. We aim to reveal the brain connectivity patterns in CI users, the change over time after implantation and the contribution of bilateral implantation to bilateral brain interaction. The research not only will contribute to better understanding of the underneath activities of the brain in speech perception but also may provide useful information about how to help CI-users benefit most from their implants. Furthermore, it can be a predictive measure of how well a CI might be of benefit to patients after implantation.