IDENTIFICATION OF FUNCTIONING CORTEX USING CORTICAL OPTICAL IMAGING

OBJECTIVE: The purpose of this study was to evaluate the technique of cortical optical imaging (COI) of intrinsic cortical optical signals r elated to neuronal activation. The specific goals of the study were to evaluate some of the technical aspects of COI and thus maximize the i ntensity of the image of this intrinsic signaling process and to deter mine the physiological reliability of COI in a well-defined animal sys tem. METHODS: The intrinsic optical signal of activated whisker barrel cortex of rat was imaged using a computer-based technique for rapid a cquisition of enhanced images. Single-unit microelectrode recordings o f cortical neuronal responses to whisker movement were used to confirm the locations of the whisker barrels. RESULTS: Narrow band incident l ight at 600- to 610-nm wavelength was most effective for producing opt ical images. Images could be obtained during activation by a single lo ng (40 s) stimulus or by averaging the signal generated by repeated sh orter (1-8 s) stimuli. Focusing slightly below the cortical surface, m inimizing movement, and abolishing extraneous light were all important in increasing the signal-to-noise ratio. The locations of whisker mov ement-evoked cortical activity determined using COI are consistent wit h the known functional anatomy of rat whisker barrel cortex. The image s obtained with this experimental arrangement are shown to be accurate predictors of the location of neuronal activity determined by compari ng the locations of active sites identified with COI with locations of areas of neuronal activity determined using single-cell recording tec hniques. CONCLUSIONS: COI is able to rapidly identify areas of cortex containing elicited neuronal activity. The technique allows cortical a ctivation maps to be made rapidly with a very high degree of spatial r esolution. COI is reliable and consistent over time. COI, if used care fully, holds promise as an intraoperative technique to study both huma n and experimental animal cortical function.