Abstracts

Laboratory studies in rodent epilepsy models have demonstrated an increase in deoxygenated hemoglobin and a decrease in tissue oxygenation during interictal spikes and ictal events. This [ldquo]epileptic dip[rdquo], like the [ldquo]initial dip[rdquo] recorded during normal sensory processing, implies that the enormous rise in cerebral blood flow (CBF) is inadequate to meet the increased metabolic demands associated with synchronized epileptic activity. Whether this phenomenon is artificial, associated with acute pharmacological models, the rodent species or anesthesia and whether it occurs in spontaneous chronic human epilepsy is unknown., We recorded intrinsic optical signals (IOS) from human cortex intraoperatively during spontaneous seizures arising from brain surrounding a small ([sim]5 mm) cavernous malformation in an awake patient using only local anesthesia with simultaneous electrocorticography (ECoG)(n=3; average duration=134[plusmn]17 seconds). The IOS was recorded at two wavelengths, one an isosbestic point for hemoglobin to measure cerebral blood volume (CBV; 570 nm) and the other at a wavelength more sensitive to deoxygenated hemoglobin (Hbr; 610 nm)., We found a clear increase in (max: 8.6[plusmn]0.6 %) throughout the length of the seizure confined to the single gyrus containing the cavernous malformation and the ECoG spikes, confirming that spontaneous human seizures cause an increase in brain metabolism that temporarily overwhelms cerebral perfusion. A large increase in CBV (max: 18 %) was also observed, which was also confined to the same gyrus. Most surprisingly, a statistically significant increase (t-test; p[lt]0.05) in CBV and Hbr actually preceded the onset of seizure by 14.2[plusmn]8.5 seconds., Our data indicates that (1) spontaneous human seizures cause a focal decrease in hemoglobin oxygenation that last for the duration of the seizure, (2) techniques sensitive to increases in oxygenation such as BOLD fMRI may mislocalize ictal onsets, (3) perfusion and oxygenation can both be used to localize focal human epilepsy, (4) perfusion and oxygenation changes occur prior to the electrographic onset of the seizure and may be useful in predicting seizure onset., (Supported by NIH.)