Intrinsic optical imaging of directional selectivity in rat barrel cortex: application of a multidirectional magnetic whisker stimulator.

Using intrinsic optical imaging methods, somatosensory-evoked neural activity was visualized in the rat barrel cortex at high spatial resolution in order to obtain cortical maps of the directional selectivity of whisker deflection. For this task, a special multidirectional mechanical stimulator was developed in our laboratory. The vibrissae were covered with magnetic paint and deflection was performed using a custom-built deflecting device with four small crosswise electromagnets; the whisker was placed at the intersection of the magnet axes. The results show that differences between responses to directional deflection were indicated by a change in the intrinsic optical signal of incident light at 546 nm corresponding to an increase in blood volume. Our results provide a preliminary indication that the different regions of the barrel have different directional preference, supporting recent electrophysiological studies suggesting that the barrel might have a fine, directionally-sensitive anatomical structure.