Connectivity-Based EEG Biofeedback
The compressed spectral array (CSA) is designed to provide a three-dimensional time/frequency representation of electroencephalography (EEG) signals, using a combination of frequency analysis, spline interpolation, and color-coded representation of signal amplitude. In a single display, typically one minute of EEG is displayed, with frequency as the horizontal axis, amplitude as the vertical axis, and time as the "z" axis. The use of connectivity introduces an entirely new dimension to neurofeedback. The brain, as a dynamical system, has both of these types of situations, and, therefore, the coherence and phase observed in an EEG signal can vary widely in its connectivity, depending on the brain locations, frequencies, and tasks being monitored. Synchrony is typified by the large, bilaterally symmetric alpha with eyes closed in a normal person. Only a limited set of EEG complements and sites are generally truly synchronous, whereas normative values for coherence can be found between any pair of sites for any compound.