Dendritic membrane properties influence multimodal integration for fast behavioral decision

MEDAN, VIOLETA; NEUMEISTER, HEIKE; PREUSS, THOMAS

College Park, Maryland

Congreso; Tenth International Congress of Neuroethology; 2012

International Society for Neuroethology

Animals integrate information from different sensory modalities to form a percept of the world that allows adaptive behavioral decisions. However, our understanding of how multimodal integration is implemented at the dendritic level is still scant. We address this question in the startle escape (Mauthner-cell) network of goldfish. The paired Mauthner-cells receive auditory and visual inputs via two separate dendrites, both accessible for intracellular recordings, in vivo. Moreover, a single Mauthner-cell action potential triggers the startle response providing a behavioral readout for the underlying threshold computation. In the behavioral experiments (N=6) we used visual loom stimuli (600 ms duration) and sound pips (200Hz, 69dB) presented either individually or together and measured the evoked startle escape rates. The rate increased with combined stimuli to 71.5% ±12 SEM, which was larger than the arithmetic sum of the escape rates for auditory (12% ±5 SEM) or visual (38% ±9 SEM) stimuli alone. This implies a supralinear integration of the input modalities. To elucidate putative non-linearities we recorded synaptic responses in the Mauthner-cell soma and compared the amplitudes of subthreshold sound EPSPs with or without an underlying visually-evoked membrane depolarization. Results show a supralinear increase of the sound EPSP in combination trials that averaged 21%, complementing the behavioral results. Since there is at least one order of magnitude difference between processing times for sound pips (~2 ms) and visual looms (100’s of ms) we next asked if the dendrites receiving visual and auditory inputs have membrane cable properties optimized to accommodate these distinct processing times. Indeed, sequential recordings along the visual and auditory dendrites (N=10) revealed space constants of 131μm ±17 SEM and 86μm ±12 SEM, respectively. These non-uniform properties of the Mauthner-cell dendrites might influence integration along different time scales ultimately allowing multimodal perception for effective decision-making.