%0 Thesis
%9 Doctoral
%A Chen, C.-C.
%B Wellcome Department of Imaging Neuroscience
%D 2009
%F discovery:18517
%I UCL (University College London)
%P 225
%T Imaging the spatial-temporal neuronal dynamics using dynamic causal modelling
%U https://discovery.ucl.ac.uk/id/eprint/18517/
%X Oscillatory brain activity is a ubiquitous feature of neuronal dynamics and  the synchronous discharge of neurons is believed to facilitate integration both  within functionally segregated brain areas and between areas engaged by the same  task. There is growing interest in investigating the neural oscillatory networks in  vivo. The aims of this thesis are to (1) develop an advanced method, Dynamic  Causal Modelling for Induced Responses (DCM for IR), for modelling the brain  network functions and (2) apply it to exploit the nonlinear coupling in the motor  system during hand grips and the functional asymmetries during face perception.  DCM for IR models the time-varying power over a range of  frequencies of coupled electromagnetic sources. The model parameters encode  coupling strength among areas and allows the differentiations between linear  (within frequency) and nonlinear (between-frequency) coupling. I applied DCM  for IR to show that, during hand grips, the nonlinear interactions among neuronal  sources in motor system are essential while intrinsic coupling (within source) is  very likely to be linear. Furthermore, the normal aging process alters both the  network architecture and the frequency contents in the motor network.  I then use the bilinear form of DCM for IR to model the experimental  manipulations as the modulatory effects. I use MEG data to demonstrate  functional asymmetries between forward and backward connections during face  perception: Specifically, high (gamma) frequencies in higher cortical areas  suppressed low (alpha) frequencies in lower areas. This finding provides direct  evidence for functional asymmetries that is consistent with anatomical and  physiological evidence from animal studies. Lastly, I generalize the bilinear form of DCM for IR to dissociate the induced responses from evoked ones in terms of  their functional role. The backward modulatory effect is expressed as induced, but  not evoked responses.