Cortical Function Mapping with Intracranial EEG - Quantitative EEG Analysis Methods and Clinical Applications - page 390

During the word perception stage of word repetition [Figure 14.6(a)], the pre-
dominant increase in ERC for 82 to 100 Hz is observed from auditory association
cortex to mouth/tongue motor cortex (E9 E3). In addition, there are other, less

prominent flows from auditory association cortex to mouth/tongue motor cortex
(E9

→

E3). Furthermore, there are also increases
in flows from auditory association cortex to mouth/tongue motor cortex “via”
supramarginal gyrus (BA40/Wernicke's area): E9

→ E5, E9 → E4, E7 → E3, and E8 →

E3. The second stage,
the “spoken response” [Figure 14.6(b)], is characterized mainly by flow increases
from Broca's area to tongue/mouth motor cortex (E2

→ E11 →

E4), but also by
smaller flow increases from Wernicke's area to mouth/tongue motor cortex (E7

→ E4, E1 →

→

E4, E11 → E4) and from mouth/tongue motor cortex to Broca's area (E4 → E2,

E3 E2), perhaps reflecting the activation of feedback pathways while the patient

speaks and hears her own spoken response.
Given the remaining uncertainties regarding the neural generators of
high-gamma responses (see Section 14.3.4.1), the interpretation of ERC flows in
high-gamma frequencies can only be provisional at this point. One can only specu-
late that if high-gamma activity at one recording site is generated by the synchronous
neural firing (output) of a cortical population that projects to a separate, down-
stream population, it may have a time-dependent causal relationship with the
high-gamma activity generated by the subsequent output of the downstream popula-
tion. Although evidence for this and other potential interpretations is still lacking,
the results that have been obtained with this and related methods to date illustrate
the potential for iEEG and advanced signal analysis to study the dynamics of cortical
networks at physiologically relevant temporal scales.

→

(a) (b)
Figure 14.6 Integrals of ERC for the frequency range 82 to 100 Hz, calculated for two stages of an
auditory word repetition task: (a) auditory perception (between stimulus onset and offset), and (b)
verbal response (following the mean response onset). Arrows indicate the directionality of ERC, and
the width and darkness of each arrow represent the magnitude of the ERC integral (only positive val-
ues are shown). ( From: [148]. © 2008 Wiley-Liss Inc. Reprinted with permission.)