Abstracts

Rationale: Afterdischarges are continuous epileptiform rhythms that can result from electrostimulation of neural tissue. They can propagate to interconnected structures, and produce seizures or clinical symptoms in parallel depending on the network involved. We measured oscillation activity patterns in distinct structures among temporal, frontal, and parietal brain regions during afterdischarges, to assess potential downstream influences on these networks. Methods: Subdural grid and depth electrode recordings (two participants with greater than 80 recording sites each) during stimulation (awake human brain mapping sessions for surgical planning purposes) were converted to sliding oscillatory power measures using wavelet analysis. Frequency bands of interest included theta (3-7 Hz), low-gamma (30-50 Hz), and high-gamma (85-175 Hz). Electrodes on or within each structure (defined using co-registered post-operative imaging) were grouped and averaged to produce dynamic estimations for each structure, for each band in parallel. Results: During cortical electrostimulation, oscillation activity was generally resilient in the frontal and temporal cortices, maintaining similar power levels among theta, low- and high-gamma in local and remote recording sites. However, when afterdischarges occurred after stimulation of the superior temporal gyrus, high gamma oscillation power was briefly decreased throughout adjacent superior temporal gyrus and middle temporal gyrus sites immediately following the stimulation itself. Ongoing theta and low-gamma locally in these gyri were not overtly affected. Among more distributed networks, high gamma power increased in prominence in the pars orbitalis during an afterdischarge that involved clinical symptoms (phonemic repetition errors). There were no major changes observed in deep temporal structures (hippocampus, amygdala). Conclusions: Afterdischarges elicited by superior temporal gyrus stimulation were associated with changes in oscillation power of local and distributed networks. Some of these changes were in structures with functions associated with the transient clinical deficit, such as pars orbitalis (role in language semantics and syntax), and the adjacent superior temporal gyrus electrodes (language comprehension processing). This method of structure-specific grouping of dynamic activity profiles provides topographical profiles of downstream influences of epileptiform discharges. Clinically, this method could help trace important pathways in seizure propagation that mirror evolving features of semiology, such as speech arrest. Funding: Dr. Chang was funded by National Institutes of Health Grant Nos. R01-DC012379, R00-NS065120, and DP2-OD00862 and the Esther A. and Joseph Klingenstein Fund.