Abstracts

Rationale:
Different techniques, most notably direct electrical stimulation and passive functional mapping, can be used to delineate functional areas prior to resective brain surgery.  Both of these methods can be performed at the bedside or in the operating room within the course of an awake craniotomy.  However, both of these methods require active patient cooperation, which can be difficult to obtain, especially within the operating room.  Thus, there is a need for a functional mapping technique that does not depend on active patient cooperation.  Single-pulse electrical cortical stimulation (SPES) has been used by many studies to establish the connectivity between functionally connected areas, and does not depend on patient cooperation.  We here hypothesized that SPES within the superior temporal gyrus (STG) elicits a neuronal response within the entire receptive auditory cortex.  We tested this hypothesis by comparing the neuronal responses to SPES and auditory speech stimuli.
Method:
We recruited six human subjects with intractable epilepsy who underwent surgical implantation of subdural electrocorticographic (ECoG) electrodes (2.4 mm exposed diameter, 6-10 mm pitch) over temporal, frontal and/or parietal cortices.  We delivered single-pulse electrical stimulation (2 Hz, 10-15 mA, 0.3 ms pulse width, 200 pulses per electrode pair) to directly adjacent electrodes within STG while recording electrocorticographic (ECoG) signals at all other locations with high sampling frequency (4800 Hz).  We also presented a series of auditory stimuli that included sounds from a variety of categories with and without language content.  From the recorded signals, we determined those electrodes that exhibited a significant neuronal response to SPES and auditory stimulation within the broadband gamma range (70-170 Hz).
Results:
We compared the functional maps derived from SPES with those derived from auditory stimulation.  Our results show that the broadband gamma response to SPES of STG identifies a similar set of functionally relevant electrodes as the broadband gamma response to auditory stimulation (p< 0.01 after FDR correction).  Further quantification of this relationship demonstrates a high sensitivity (84%) and specificity (72%) of SPES as an index for functional activation of auditory-related cortex (see Figure 1A,E,G).  We also found functionally connected cortical areas related to auditory stimulation and SPES to be strongly correlated (r=0.66, p< 0.001, Figure 1D,F,H).
Conclusion:
In summary, the results of our study show that SPES and auditory stimulation activate similar cortical networks.  These results provide encouraging evidence for SPES as a method to functionally map the cortex without active patient cooperation.  Thus, with further validation in more subjects, the approach presented here may lead to a new method for intraoperative functional mapping.  Future studies may explore the possibility of extending this mapping to patients under general anesthesia.
Funding:
:This work was supported by the NIH/NIBIB (P41-EB018783, R01-EB026439), the NIH/NINDS (U01-NS108916 and U24-NS109103), the NIH/NIMH (P50-MH109429), the NIH/NICHD (DP1-HD091947), Fondazione Neurone, and the National Natural Science Foundation of China (51620105002). We thank all the patients who participated in the study.