Precise placement of multiple electrodes into functionally predefined cortical locations.

Current research on topics such as effective connectivity, neuronal coding strategy or signal propagation in the central nervous system requires simultaneous recordings from multiple sites within functionally grouped but topologically distributed neuronal clusters. We have addressed this issue by characterization of the cortical functional architecture using optical imaging of intrinsic signals (OI) and subsequent placement of multiple, individually adjustable electrodes into pre-selected domains. In order to achieve maximum precision and flexibility for the positioning of electrodes, a plastic cylinder containing channels of an extremely high aspect ratio (density >20 channels/mm(2)) was fixed above the cortex and individual channel positions were superimposed onto the functional maps of orientation columns obtained previously with OI. Subsequently, channels corresponding to the desired locations in the functional map were used as guide tubes for electrode insertion. The spatial precision of this approach was in the range of 100 microm and experiments in cat primary visual cortex revealed a close correlation between the desired and the actually recorded orientation preferences of the targeted columns. The method is applicable to all cortical areas in which OI is feasible and offers a high degree of flexibility with respect to the number and geometry of applicable probes. It is, thus, an excellent tool for studying distributed codes and interactions between multiple predefined recording sites.