Abstracts

Spiral waves are a basic feature of nature and have been observed in a variety of biological systems, but spiral dynamics have not been studied in mammalian cortex. If spirals exist in the cortex, the robust dynamics of the spiral waves may contribute to sustaining seizure activity, strategies of disrupting formation of spirals may be used to disrupt seizure activity., We used optical imaging with voltage-sensitive dyes to examine seizure-like events induced by carbachol and bicuculline in rat neocortical slices and in rat cortex in vivo. Slices from visual cortex were sectioned in a tangential plane containing cortical layers III-V. The slices were stained with an absorption dye, NK3630 before imaging, and the signals from the stained tissue were recorded by a photodiode array. In vivo imaging was performed over visual cortex in adult rats. The animals were anesthetized with urethane while a craniotomy window of 5 mm in diameter was created. The cortex was stained by a fluorescent dye RH1691, and fluorescent signals were recorded by a photodiode array., The seizure-like oscillations occurred spontaneously in vitro and in vivo when the drugs were applied. The oscillations were organized spatiotemporally as propagating waves, and complex wave patterns such as spiral, plane, ring and irregular waves were observed both in slices and in vivo. These wave patterns alternated within one oscillation epoch, suggesting the patterns were dynamically organized. Spiral waves, occurred in about 50% of recording trials in slices but were rarely seen in vivo. We examined the initiation of spiral waves in slices and found that collision of two wave fronts usually occurred prior to the initiation of spiral waves. The spiral waves were very stable in slices, some sustained for up to 30 rotations, but spirals in vivo only lasted for a few cycles. In brain slices, [apos]phase singularity[apos], a hallmark of spiral waves, can be clearly identified at spiral center as substantial reduction in signal amplitude and a circular phase distribution around it. Phase analysis of the spiral center and surrounding areas suggested that the amplitude reduction was caused by superimposition of multiple widely distributed phases., Our results suggest that spiral dynamics may exist in neocortex during seizure-like activity and may contribute to the sustaining of seizure events., (Supported by a fellowship from Epilepsy Foundation and NIH NS36447.)