Chris Rennie

Where am I?

I work for the Dept of Medical Physics in Westmead Hospital, Sydney, Australia, mainly supporting and contributing to the work of the Brain Dynamics Centre.

I am also an Honorary Associate at the School Of Physics, The University of Sydney.

Where have I been?

For many years my main responsibilities were to assist the work of the Brain Dynamics Centre by providing hardware and software support. This group used EEG recordings from subjects (both patients and healthy volunteers). These recordings were made during the presentation of stimuli and tasks that exercised various aspects of brain function. Often the measurements involved the simultaneous recording of eye movements, pupil size, skin conductance, ECG, and respiration. The complexity involved in these additional modalities — combined with the problems of generation and synchronization of audio-visual stimuli — made for an interesting job. The job was made even mode interesting by the rapid advances in hardware, which meant that I implemented acquisition and analysis software for several hardware generations:

• Custom-built Z80-based computer, with CP/M and Pascal software
• PDP11 computer, with RT11 and Data Translation hardware and Fortran
• IBM-AT, with a Burr-Brown ADC, DOS and software in C
• IBM-AT, with SynAmps ADC, DOS and software in C
• Pentium PC, with NuAmps and commercial acquisition software

Then, in a weak moment, I commited to a PhD. My project was to model the EEG - the large-scale electrical activity of the brain. The word 'large-scale' turns out to be crucial, since it makes the undertaking feasible: by considering only the low spatial and temporal frequencies (which is all that is visible in scalp recordings) we are able to make the 'mean field' approximation, whereby only the averaged (or correlated) activity is modelled. This is far simpler to model than single-neuron activity. The reasons are explained in my thesis, which is available in PostScript format and in PDF format.

The thesis is also available from the URI http://hdl.handle.net/2123/816.

This work plus that of my supervisors and colleagues resulted in a Eureka prize. Eureka prizes are awarded annually for scientific research in Australia. Our work was awarded the 2003 Eureka in the category of Interdisciplinary Scientific Research. The team was Professor Peter A Robinson, Professor Jim Wright, Dr Evian Gordon and myself. For more about this award see http://www.amonline.net.au/eureka/

During my PhD candiditure I also gained valuable experience in librarianship. As a result you can see the contents of our Theory library: either the HTML version, the PostScript version or BibTeX version

Compiling and maintaining a reference list is hard work. You are welcome to use mine as a starting point.

• The main BibTeX file is refs.bib
• Aliases for abbreviated journal names are in journs.bib
• Aliases for full journal names are in journals.bib
• A PostScript version of these references is in refs.ps

Where am I going?

• I am attempting to learn more about the physics of MRI, and the numerous intricacies of MRI analysis.
• Our model of EEG is still being refined, and I am particularly involved in the inverse modelling problem. To get some feel for the nature of the task, try running my Java applet, which allows you to vary the model parameters yourself.
• Another refinement is to look at impulse responses — as might result from discrete stimuli — and dynamic gains — as might be expected from the transient action of neuromodulators such as ACh and NA following such stimuli. Try running my Java applet.
• The model also needs a better treatment of cortical anatomy, as it can influence the character of signals recorded on the scalp. This involves evaluating the volume conduction of the extracellular currents induced by neuronal activity. See the triangulated cortex that I am working on.
• It is interesting to compare and contrast models of large-scale brain activity. I have a draft document, in PostScript format here.
• Another interest is better quantification and classification of EEG signals, using either physiological or phenomenological models. Statistics and data mining come into it, ultimately. See some programming notes for a program known as jeda.

Miscellaneous

• A brief guided tour of the Linux command line is here.
• How to do PostScript and PDF manipulations is described here.
• How to generate PostScript conveniently from .tex files is described here.
• A tutorial on the use of Fourier series for time series analysis is here. It is not yet fully functional.
• Check out Peter Loxley's new web page!

The Brain Dynamics Gang