Abstracts

Rationale: The baboon represents a natural model for idiopathic generalized epilepsy with photosensitivity. This study aims to evaluate regional cerebral blood flow (CBF) changes related to seizures and interictal epileptic discharges (IEDs) recorded in baboons with PET perfusion imaging.Methods: IEDs and myoclonic seizures were recorded during the resting PET scans of seven photosensitive epileptic baboons and one asymptomatic control animal. One to three resting scans were included for each animal. Subanesthetic doses of ketamine (4.6-9.1 mg/kg/hr) were used for sedation. PET images were acquired in 3D mode (CTI/Siemens HR+ scanner, 63 contiguous slices, 2.4mm thickness) and then co-registered with MRI (3T Siemens Trio, T1-weighted 3D Turboflash sequence, TE/TR/TI = 3.04/2100/785 msec, flip angle=13 degrees). Regional CBF changes were correlated with IED rates for all 8 baboons, then compared between averaged scans with seizures (N=5) and ≥4 IEDs/acquisition (N=6), and between averaged scans with ≥4 and 1-3 IEDs/acquisition (N=6). All images were processed by Multiple Image Processing Station (MIPS) (RIC, San Antonio). Results: IED rates were correlated with regional CBF increases in the bilateral occipital and parietotemporal and sensorimotor cortices, and with decreased CBF in the frontal lobes, including the right anterior cingulate and bilateral orbitofrontal gyri, respectively (Figure 1). Scans with seizures and ≥4 IEDs demonstrated a weak activation in the right precentral gyrus, in the bilateral thalami, bilateral globus pallida, and right striatum, compared to those with ≥4 IEDs without seizures. Scans with ≥4 IEDs demonstrated increased CBF in the left anterior cingulate, bilateral orbitofrontal cortices and hypothalamus, and with decreased CBF in the right caudate, compared to scans with 1-3 IEDs. Conclusions: This preliminary assessment of regional CBF changes associated with seizures and IEDs in the baboon demonstrates activation of the occipital and temporoparietal cortices in addition to the sensorimotor cortices. Whether these areas are associated with the generation or propagation of the discharges is unclear. While increased IED rates may recruit the orbitofrontal cortices and hypothalamus, seizures appear to activate extensive subcortical networks commonly involved in cortical inhibition. Acknowledgements: This study was supported by the National Institutes of Health (P51 RR13986 through the SFBR to CAS, and 1 R01 NS047755-01 to JTW).