IMAGING THE DORSAL HIPPOCAMPUS - LIGHT REFLECTANCE RELATIONSHIPS TO ELECTROENCEPHALOGRAPHIC PATTERNS DURING SLEEP

We assessed the correspondence of 660 nm light reflectance changes fro m the dorsal hippocampus with slow wave electroencephalographic (EEG) activity during quiet sleep (QS) and rapid eye movement (REM) sleep in four cats. An optic probe, attached to a charge-coupled-device (CCD) video camera, was placed on the dorsal hippocampal surface to collect reflectance images simultaneously with EEG, which was measured by macr oelectrodes placed around the probe circumference. Spectral estimates of EEG and light reflectance amplitude indicated that reflectance chan ges occurred in a similar frequency range as EEG changes. Dividing the image into 10 subregions revealed that reflectance changes at the rhy thmical slow wave activity band (RSA, 4-6 Hz) persisted in localized r egions during QS and REM sleep, but regional changes showed considerab le wave-by-wave independence between areas and from slow wave electric al activity. Peak frequencies for reflectance changes corresponded to fast RSA frequencies observed in the EEG. Optical changes most likely derive from fast-acting physical phenomena, rather than from alteratio ns in blood perfusion, and provide increased spatial resolution over t hat offered by electrical measurements.