New approaches to non-stationary analysis of neurological signals

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With current imaging technology and instrumentation, there is a wealth of information that can be obtained non-invasively from the human body. But how do we best interpret this data to obtain a better understanding of the functioning of the body both for scientific exploration and for the improvement of human health? A challenge with biomedical signals is that they are often non-stationary in nature. We attempt to tackle this problem by developing new theoretical approaches and applying these approaches to understand and classify human disease states in a manner not previously possible. One area of our work has been to better characterize the time-frequency behaviour of acoustic signals like speech. By mimicking the functioning of the human ear, we have developed new signal processing techniques which allow us quantify low-frequency vocal tremors of patients suffering from Parkinson's disease. Currently there is no known cure for Parkinsonism, nor is there a reliable method (invasive or non-invasive) to diagnose the disease. By studying low-frequency amplitude and frequency modulations in the speech envelope, we can correctly diagnose more than 95% of early case Parkinson's disease. Support for research in this area over the next few years will allow us not only to better understand the disease but to dramatically improve its early diagnosis. We have also been developing other techniques to analyze more general non-stationary signals like brain evoked potentials. Classical approaches in terms of Fourier analysis do not provide a clean representation of such neurological signals. Instead we have pioneered an approach to decompose these signals into a sum of elementary signals known as chirplets. We have shown that this technique can help elucidate the impairment of cortical inhibition in patients with schizophrenia. By investigating the possible underlying neuromechanism(s) underlying schizophrenia, our results may help suggest new types of treatment that can restore the necessary inhibition for healthy brain function in the near future.