Abstracts

Rationale: Identifying the epilepsy focus with high spatial resolution is a challenge in clinical practice, especially in the cases where no anatomical abnormality can be detected. Neurovascular coupling based functional brain technology (e.g., fMRI, SPECT) is often applied in clinic but the neurovascular coupling mechanism during ictal events is still unclear. Our lab previously demonstrated that the cerebral volume increased co-localized with neuronal activity in anesthetized model. In this study, we investigate the neurovascular coupling mechanism during acute ictal events in unanesthetized mice.  Methods: Seven transgenic mice expressing GCaMP6f in subset of excitatory neurons were employed in the study. A 5x7mm craniotomy window was created over both hemispheres and the window was sealed with a clear silicone-based polydimethylsiloxane (PDMS) film for long term imaging. Three weeks after the surgery, the mice will be fixed on a clamp for imaging.2mM 4AP (0.5ul) was injected in the neocortex to induce ictal events. We used simultaneous calcium (illumination at 470 nm) and intrinsic signal at 530 nm and 610 nm imaging to record the neuronal and hemodynamic changes during ictal events.  Results: The ictal event contained a train of spikes. Each spike showed a propagation wave of calcium increase. The spatial extent of each spike gradually increased over time. In some cases, the ictal event propagated to the contralateral cortex. Different propagation patterns could be recorded when crossing the hemisphere. In some ictal events, the brain area close to the midline in the contralateral hemisphere became involved first, showing a smooth propagation rather than a jump across the corpus callosum (CC). In some events, the brain area mirroring the 4AP injection site involved the ictal events first, showing CC jumping propagation to a mirror focus. The total hemoglobin (Hbt) showed an increase with ictal events. The spatial extent of Hbt change closely resembled the spatial spread of calcium signal. The oxy-hemoglobin changes also showed an increase with ictal events, but spatially overestimated the calcium activity. The deoxy-hemoglobin (Hbr) signal showed complex spatiotemporal dynamics. In the surrounding area, a decrease in Hbr was observed throughout the seizure. In the epi-focus, both increase and decrease in Hbr were observed.  Conclusions: Our data indicated that cross hemisphere propagation may involve either contiguous spread or cross callosal white matter spread. Neuronal activity induced Hbt changes best represent the spatial involvement of seizure activity, indicating that cerebral blood volume based imaging techniques may be better than BOLD based imaging techniques for seizure mapping.  Funding: No funding