We examined directional sensitivities in the dendritic activity of the identified giant interneurons (GIs) in the cricket, using in vivo Ca 2+ imaging during different directional air-current stimuli. Air current stimulus evoked action potential burst and quick Ca2+ increase in GI. The stimulus direction of the maximal Ca2+ responses corresponded to that of the maximal voltage response. However, the shapes of the directional tuning curves based on the Ca2+ responses for each dendritic branch were different from the overall tuning curve based on spike counts for the cell. Moreover, different dendritic branches displayed distinct directional sensitivity profiles to the air-current stimuli. We propose that postsynaptic activities will influence the local Ca2+ signals in the distal dendrites, and produce the difference in directional sensitivity of the dendritic Ca2+ response.
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