Optical Monitoring of Stimulus Evoked Neural Activities in Isolated Retina

We recently demonstrated near infrared (NIR) light imaging of fast intrinsic optical responses (FIORs) closely correlated with electrophysiological changes in visible light activated frog retina. Using a fast CCD camera, dynamic FIORs could be routinely observed in single pass experiments with 1 mum and 10 ms resolution. Fast NIR optical imaging sequences typically disclose maxima of FIORs at the level of 1.0% dI/I, where dl is the transient optical change and I is the baseline light intensity. Both positive and negative FIORs were observed in activated retina. Using fast (~ms) visible light flash stimulus, positive FIORs dominated the retina, although negative FIORs were also detected in high resolution functional images. In contrast, negative optical responses dominated the retinal area activated by a long (2 s) step of light stimulus, while positive optical responses were observed in surrounding area. For both experiments, dynamic FIORs initiated from the center of the retinal area covered by the visible light spot, and gradually spread to surrounding area.