Motion analysis of escape movements evoked by tactile stimulation in the cockroach Periplaneta americana.

The escape behavior of the American cockroach, Periplaneta americana, has provided a large amount of neuroethological data on the control of orientation movements. In the typical behavior, the animal responds to gentle wind puffs by turning away from the wind source and running (Camhi and Tom, 1978). However, cockroaches also escape in a directional manner in response to tactile stimuli (Comer et al. 1989, 1993). This additional category of escape response raises two important questions. Do the neural circuits for windand tactile-evoked escape responses converge, and if so where? At one extreme, the two behaviors may be under the control of completely separate circuits. Alternatively, the two sensory pathways could converge on a single set of controlling interneurons. To address this question, circuit analysis studies must be complemented with behavioral observations. Shared neurons could certainly be demonstrated by analyzing the neural pathways from sensory structures to motor output. However, during the actual behavioral response, tactile information could still bypass common elements and utilize a separate pathway from that used during the wind-evoked response. If the escape turns resulting from tactile stimulation include totally different leg movements from those generated by wind, it would be difficult to rationalize common control elements. However, a finding that the leg movements that generate turns are essentially the same regardless of the sensory modality that triggered them would support the notion of common control circuits. A detailed circuit analysis study would then be in order. In this paper, we report behavioral observations of the initial turns of the tactile-evoked escape behavior in both freely moving and tethered animals. We then compare these leg movements with those that have been documented for wind-evoked escape turns. In the interest of space and clarity, we will continue to refer to these behaviors as the tactileand wind-evoked escape responses. However, we should point out that our analysis is directed specifically at the initial turn of the escape response not the subsequent running movements. The leg movements that produce wind-mediated turns have been documented in detail