Focal neocortical seizures, induced by injection of 4-aminopyridine, were imaged in the rat neocortex using the intrinsic optical signal, with incident light at various wavelengths. We observed focal, reproducible and prolonged reflectance drops following seizure onset, regardless of wavelength, in the ictal onset zone. A persistent drop in light reflectance with incident orange light, which corresponds to a decrease in oxygenated hemoglobin, was observed. We describe this phenomenon as an ‘epileptic dip’ as it is reminiscent of the ‘initial dip’ observed using the intrinsic optical signal, and also with blood oxygen level-dependent functional magnetic resonance imaging, after normal sensory processing, although with much longer duration. This persistent ictal ischemia was confirmed by direct measurement of tissue oxygenation using oxygen-sensitive electrodes.
Department of Neurological Surgery, Weill-Cornell Medical College, New York Presbyterian Hospital, New York, New York, USA
Correspondence and requests for reprints to Sonya Bahar, PhD, Center for Neurodynamics, Department of Physics and Astronomy, University of Missouri at St Louis, One University Boutevard, St Louis, MO 63121, USA
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Sponsorship: NIH/NINDS Grants K08NS43799 and R21NS044812 to T.H.S.
Received 6 December 2005; accepted 30 January 2006