Biomedical Engineering Reference
In-Depth Information
CHAPTER 14
Cortical Function Mapping with
Intracranial EEG
Nathan E. Crone, Anna Korzeniewska, Supratim Ray, and Piotr J. Franaszczuk
Although PET and fMRI images of human brain function have captured the imagi-
nation of both scientists and the lay public, they still offer only indirect and delayed
measures of synaptic activity. EEG (and MEG) offer the only real-time noninvasive
measures of human neuronal activity, and the multidimensional complexity of their
signals potentially yields far more information about brain function than the scalar
measure of neuronal metabolism. Advances in EEG/MEG signal analysis have
allowed investigators to mine the riches of these signals to study not only which
individual brain regions “light up” during cognitive operations, but also how com-
plex cognitive operations can arise from the dynamic and cooperative interaction of
distributed brain regions.
The strengths of EEG and MEG as tools for cortical function mapping, how-
ever, have often been offset by the inverse problem for identifying their signal
sources. Under the unusual circumstances of patients undergoing surgery for epi-
lepsy, this limitation can largely be circumvented by recording from electrodes that
are surgically implanted in or on the surface of the brain. This chapter reviews how
this and other advantages of intracranial EEG (iEEG) have been exploited in recent
years to map human cortical function for both clinical and research purposes.
14.1
Strengths and Limitations of iEEG
The circumstances under which iEEG is clinically necessary are relatively few [1]
and consist primarily of patients undergoing surgical treatment for intractable epi-
lepsy, brain tumors, or vascular malformations of the brain. These circumstances
account for the most important limitation of iEEG, which is that the recorded sig-
nals and their responses to functional brain activation may be affected by abnormal-
ities of brain structure and neurophysiology that accompany brain disease. For
example, iEEG recordings in patients with intractable epilepsy may be contami-
nated by epileptiform discharges or may be distorted by functional reorganization
due to chronic seizures. Nevertheless, the improved spatial resolution of iEEG and
its higher signal-to-noise ratio, particularly for high-frequency activity, provide an
unprecedented opportunity for studying the spatial and temporal characteristics of
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