Event
Special Neural Systems Lab Lecture: Alain de Cheveigne, "Quadratic Component Analysis"
Thursday, March 1, 2012
4:00 p.m.
1146 A.V. Williams Building
Pam White
301 405 6576
pwhite@umd.edu
Neural Systems Lab Special Lecture
Finding a needle in the electrophysiological haystack: Quadratic Component Analysis
Alain de Cheveigne
Department of Cognitive Studies
Ecole Normale Superieure
Paris, France
Abstract
Multichannel recording techniques (electrode arrays, optical imaging, MEG, etc) are plagued by poor signal to noise ratio, as the activity of interesting sources is buried in that of competing brain sources and noise. Analysis tools are needed to leverage the high dimensionality and isolate the activity of interest.
I present a method for analyzing multichannel recordings in response to repeated stimulus presentation.
Quadratic Component Analysis (QCA) extracts responses that are {\em stimulus-induced}\ (triggered by the stimulus but not precisely locked in time), as opposed to stimulus-evoked (time-locked to the stimulus). Induced responses are often found in neural response data from magnetoencephalography (MEG), electroencephalography (EEG), or multichannel electrophysiological and optical recordings. The instantaneous power of a linear combination of channels can be expressed as a weighted sum of instantaneous cross-products between channel waveforms. Based on this fact, a technique known as Denoising Source Separation (DSS) is used to find the most reproducible "quadratic component" (linear combination of cross-products). The linear component with a square most similar to this quadratic component is taken to approximate the most reproducible evoked activity. Projecting out the component and repeating the analysis allows multiple induced components to be extracted by deflation.
The method is illustrated with synthetic data, as well as real MEG data. At unfavorable signal-to-noise ratios, it can reveal stimulus-induced activity that is invisible to other approaches such as time-frequency analysis. QCA is part of an onging effort to produce tools to unravel the complex mixtures produced by multichannel electrophysiological techniques.
