Neural mechanisms for multi-sensory selection of behavior in microbrain system.

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<Behavioral Analyses>The insects can detect humidity gradient in their environment and prefer area of certain humidity. We analyzed the humidity-location behavior of the cockroach, Periplaneta americana. The insect put into the arena, in which there was humidity gradient, stayed in higher humidity part after it had run along the periphery of the arena. This behavior was resulted from 1) the behavior without spatial movement was increased, 2) the walking velocity was decreased, and 3) the meander (deg/cm) was increased in higher humid area than in lower humid area. The behavioral sequence for the insect to reach water consisted of 1) stopping to move after detection of water, 2) moving its antennae and neck to search humidity gradient in the standing posture, and 3) walking toward higher humidity area.<Physiological and Morphological Analyses>The deutocerebral projection neurons responsive to humidity or temperature were identified in Periplaneta americana, using intracellular recording and staining methods. We have already showed that the hygro- and themoreceptor neurons terminate in specific glomerular complexes in the antennal lobe, respectively. In this study we found that dendrites of the deutocerebral projection neurons innervated into these complexes and their axons innervated both into the mushroom body and the lateral lobe of protocerebrum. Furthermore axonal terminal areas in the lateral lobe were different between the hygro-responsive projection neurons and thermoreceptive projection neurons. This shows that there are functional segregations in the lateral lobe.