Signal source separation in the analysis of neural activity in brain

This research examines the spatial and temporal characteristics of the responses to stimulation of the barrel cortex in anesthetized rats using optical imaging with particular emphasis on methods of analysis which reduce the effects of low-frequency oscillations on localization of the activated cortical region. Image sequences were captured using a light source with a narrow bandwidth of wavelength (590 +/- 2 nm). On each trial image data were collected at 15 Hz and stored over a 12-s period starting 8 s before stimulation onset. Stimulation was for 1 s using an oscillating whisker vibrator (approximately 1-mm deflection at 5 Hz). For each subject a total of 30 experimental trials were collected and averaged. There was an interstimulus interval of 26 s. The trial-averaged data were analyzed using two related signal source separation algorithms. Both algorithms use a weak model of the expected temporal response as a filter to exclude contributions from low-frequency baseline oscillations which we call the V-signal. We found that both algorithms successfully separated most of the effects of the V-signal from the response to the stimulation. The performance of the algorithms compared favorably with the performance of related algorithms without weak constraints and the "ratio of means" strategy used by C. H. Chen-Bee et al. (1996b, J. Neurosci. Methods 68:28-37; C. H. Chen-Bee et al., 2000, J. Neurosci. Methods 97:157-173).