Broadband changes in the cortical surface potential track activation of functionally diverse neuronal populations.

We illustrate a general principal of electrical potential measurements from the surface of the cerebral cortex, by revisiting and reanalyzing experimental work from the visual, language and motor systems. A naive decomposition technique of electrocorticographic power spectral measurements reveals that broadband spectral changes reliably track task engagement. These broadband changes are shown to be a generic correlate of local cortical function across a variety of brain areas and behavioral tasks.

Task-related principal component analysis: formalism and illustration.

We address the application of a modified form of Principal Component Analysis (PCA) to data which is characterized by sparse, but known, event times. The sparsity of such event times makes it unlikely that they have a major contribution to the overall covariance in the data, and standard PCA components generated from this covariance may not give us useful insight about the task. A simple method is shown here which generates an orthogonal, "task-related PCA" (trPCA) transform based upon correlations between non-simultaneous, event-time locked, subsets of data.

Real-time functional brain mapping using electrocorticography.

We demonstrate the feasibility of real-time cortical mapping from arrays of subdural electrodes using the electrocorticographic signal power in the higher spectral frequencies (76-200 Hz, or "chi-index"). Hand area was mapped offline in eight individuals using brief baseline and hand-movement measurements. In one patient, hand sensorimotor cortex was identified online during a handshake.

Cortical electrode localization from X-rays and simple mapping for electrocorticographic research: The "Location on Cortex" (LOC) package for MATLAB.

Medically refractory epilepsy accounts for more than 30% of the epilepsy population. Scalp EEG electrodes have limited ability to localize seizure onset from deep structures and implantation of subdural electrodes with long term monitoring provides additional information. Apart from clinical application, this patient population provides a unique opportunity for acquiring electrocorticography data in research paradigms.