Biomedical Engineering Reference
In-Depth Information
14.5
Future Applications of iEEG
Research utilizing quantitative analyses of iEEG recordings will continue to delin-
eate the functional response properties of different electrophysiological correlates
of cortical processing. These studies are expected to provide a basic foundation for
future applications of iEEG and noninvasive electrophysiological recordings.
High-gamma responses have now been observed in a variety of different functional
neuroanatomic domains with relatively consistent functional response properties.
This suggests that HGRs may serve as a general purpose index of cortical activation
and information processing. However, much is still unknown about the neural sub-
strates and functional response properties of this response, and the same can be said
about the other electrophysiological indices that have been studied with iEEG and
qEEG in general. Future applications of these responses may depend on a better
understanding of their dependence on the cytoarchitectonics, functional connectiv-
ity, and types of processing in different cortical regions. Elucidation of these rela-
tionships will likely require further basic investigations in animals. Nevertheless,
some applications of iEEG are moving forward without this information. For exam-
ple, Miller et al. [60] recently showed that high-gamma ERS is sufficiently robust
that it can be seen in single trials, for example, during a single handshake. This
opens the door to real-time mapping of motor function. If the signal-to-noise ratio
of single-trial HGRs is adequate, they could serve as a useful electrophysiological
index for intraoperative brain mapping and for brain-computer interfaces. Indeed,
a recent study has shown that high-gamma activity can be used to discriminate the
direction of two-dimensional movements of a joystick [63].
The clinical applications of quantitative iEEG are currently limited to the rela-
tively small number of patients undergoing epilepsy surgery. However, recent stud-
ies have demonstrated the feasibility of using MEG [71, 149] or even scalp EEG
[150] to record high-gamma activity, suggesting that improved recording technol-
ogy may soon greatly expand the clinical applications of high-gamma activity, as
well as the utility of ERD/ERS, ERPs, and electrophysiological responses in general
for exploring the neural mechanisms and functional dynamics of higher cognitive
functions in humans.
Elucidation of functionally relevant patterns of organization in iEEG signals,
like those of other complex electrophysiological signals, has required, and will con-
tinue to require, advanced signal processing methods implemented by a team of
neuroscientists and biomedical engineers. Broader application of iEEG to the scien-
tific study of human perception and cognition will require collaborations with cog-
nitive scientists, experimental psychologists, and systems neuroscientists.
Acknowledgments
The authors thank the editors, Nitish Thakor and Shanbao Tong, for their invita-
tion to contribute this chapter, as well as the anonymous reviewer for valuable sug-
gestions. Our research was supported by R01-NS40596.
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