The overall objective of our research is to identify and validate electrophysiological signatures of human cortical processing and to use them to study the neural mechanisms of motor, sensory, and language functions. In other words, we are trying to interpret the electrical signals generated by the brain while it is at work.  If
we can reliably determine which changes in the brain's electrical signals
indicate that it is activated by a task, we can use these electrical
indices of brain activation to learn more about how the brain accomplishes
complex cognitive tasks such as producing words. For example, we think
that a seemingly simple task such as saying the name of an object, a.k.a.
object naming, requires the orchestration of several different brain
regions performing different cognitive operations in a particular sequence.
To study how the brain performs this and related cognitive tasks, we
need like to know where, when, and how much the brain is activated during
these tasks.Although PET and fMRI have been used effectively to localize neural activity during cognitive tasks, time lags between synaptic activity and changes in neural metabolism and blood flow have fundamentally limited their temporal resolution, and thus their ability to discriminate the sequence of neural activity during complex cognitive tasks. Electrophysiological techniques such as electroencephalography (EEG) and magnetoencephalography (MEG) provide a more direct measure of neural activity, with temporal resolution that is limited only by the sampling rate and specific signal analyses used. However, the analysis of their signals is complex, both in terms of source localization and their correlation with neural processing. Source localization is greatly facilitated in electrocorticographic (ECoG) recordings. These recordings are made with electrodes that are surgically implanted on the surface of the brain in order to map brain function prior to removal of brain tissue for the treatment of intractable epilepsy, brain tumors, or vascular malformations. Although these recordings are limited to very unusual clinical circumstances, they allow recordings with unprecedented density and proximity of the electrical sensors to cortical sources. Nevertheless, there remains the problem of interpreting the functional significance of the signals themselves, i.e. what signal components constitute an index of cortical processing? |