CURRENT SOURCE DENSITY PROFILES OF OPTICAL-RECORDING MAPS - A NEW APPROACH TO THE ANALYSIS OF SPATIOTEMPORAL NEURAL ACTIVITY PATTERNS

Spatio-temporal spreading of activity in the CA1 region of the rat hip pocampal slice was studied by two experimental approaches. At identica l locations in the tissue we measured both the extracellular field pot ential distribution with microelectrode recordings and the intracellul ar potential distribution by optical recording, using voltage-sensitiv e fluorescent dyes. Current source density analysis (CSD) was applied to the extracellular field potential distributions (eCSD) to enhance t he spatial resolution. In order to obtain an analogous improvement for the optical recordings, we developed a new CSD transformation, which calculates the locations of the transmembrane current generators from the intracellular potential distributions (iCSD). Compared to the unde rlying fluorescence maps, the new iCSD profiles exhibit a considerable improvement in spatial resolution. Results can be directly interprete d in terms of physiological membrane processes, such as postsynaptic p otentials and action potentials. The iCSD profiles show a surprisingly good correspondence with the classical eCSD profiles both qualitative ly and quantitatively, the only difference being that cell body activi ty is reduced in amplitude. Thus, this new optical CSD analysis paves the way for a quantitative interpretation, rather than the hitherto pr edominantly qualitative interpretation of spatio-temporal activity pro files from optical recording measurements.