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The escape behavior of the cockroach Periplaneta americana was studied by means of high speed filming (250 frames/s) and a computer-graphical analysis of the body and leg movements. The results are as follows: 1. The behavior begins with pure rotation of the body about the posteriorly located cerci, followed by rotation plus forward translation, and finally pure translation (Figs. 1, 2). 2. A consistent inter-leg coordination is used for the entire duration of the turn (Fig. 3A). At the start of the movement, five or all six legs execute their first stance phase (i.e. leg on the ground during locomotion) simultaneously. By the end of the turn the pattern has changed to the alternate 'tripod' coordination characteristic of insect walking. The change-over from all legs working together, to working alternately, occurs by means of a consistent pattern of delays in the stepping of certain legs. 3. The movements made by each leg during its initial stance phase are carried out using consistent movement components in the anterior-posterior (A-P) and the medial-lateral (M-L) axes (Fig. 4A). The movement at a particular joint in each middle leg is found to be diagnostic for the direction of turn. 4. The size and direction of a given leg's M-L movement in its initial stance phase depends on the same leg's prior A-P position (Fig. 5). No such feedback effects were seen among different legs. 5. Animals that are fixed to a slick surface on which they make slipping leg movements show the same inter-leg coordination (Fig. 3B), direction of initial stance movement (Fig. 4B) and dependence of the leg's initial M-L movement on its prior A-P position (Fig. 6), as did free-ranging animals. 6. Cockroaches that are walking at the moment they begin their escape reverse those ongoing leg movements that are contrary to escape movements. 7. These results are discussed in terms of the overall coordination of the complex movements, and in terms of the known properties of the neural circuitry for escape. Possibilities for neurobiological follow-up of certain of the findings presented here are also addressed.

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1. The escape behavior of the cockroach, Periplaneta americana, is known to be modulated under various behavioral conditions (Camhi and Volman 1978; Camhi and Nolen 1981; Camhi 1988). Some of these modulatory effects occur in the last abdominal ganglion (Daley and Delcomyn 1981a, b; Libersat et al. 1989) and others in the thoracic ganglia (Camhi 1988). Neuromodulator substances are known to underlie behavioral modulation in various animals. Therefore, we have sought to determine whether topical application of putative neuromodulators of the escape circuit enhance or depress this circuit, and whether these effects differ in the last abdominal vs. the thoracic ganglia. 2. Topical application of the biogenic amines serotonin and dopamine to the metathoracic ganglion modulates the escape circuitry within this ganglion; serotonin decreases and dopamine enhances the response of leg motoneurons to activation of interneurons in the abdominal nerve cord by electrical or wind stimulation. 3. The neuropil of the thoracic ganglia contains many catecholamine-histofluorescent processes bearing varicosities, providing a possible anatomical substrate for dopamine release sites. 4. Topical application of octopamine to the terminal abdominal ganglion enhances the response of abdominal interneurons to wind stimulation of the cerci. In contrast, serotonin and dopamine have no effect at this site. 5. It is proposed that release of these biogenic amines may contribute to the known modulation of the cockroach escape response.

1. The pattern of connectivity between identified cercal afferents and the three largest giant interneurons (GIs 1, 2, and 3) of the American cockroach was investigated by intracellular methods. These three GIs all have different directional response sensitivities and appear to be especially important in initiating the short latency escape behavior of the American cockroach. 2. One of the interneurons, GI 1 responds to wind from all four quadrants of space about the animal. However, it clearly shows a greater ipsilateral versus contralateral (relative to the GI's axon within the nerve cord) wind sensitivity. In contrast, the directional sensitivity of GI 2 is more nearly bilaterally symmetrical. Both of these interneurons receive excitatory synaptic input from the sensory cells of the nine most prominent columns (a, d, g, f, h, i, k, l, and m) of filiform hairs of the ipsilateral cercus. 3. The nine ipsilateral inputs all made roughly equivalent strength excitatory connections with GI 1. The connectivity pattern to GI 2 was the same as that to GI 1 except that the connection strength for two of the nine columns, h and i, was substantially stronger to GI 2 than to GI 1. The remaining seven sensory columns all make equivalent strength connection with GI 2. 4. Only select columns of contralateral sensory cells made synaptic connection with GIs 1 and 2. All detectable connections produced subthreshold depolarizations. 5. The response curve of GI 3 is more sharply restricted in space than that of either GI 1 or 2 and this interneuron only responds to wind stimuli originating from in front of the animal. GI 3 received excitatory synaptic input only from ipsilateral columns d, f, g, i, and k, all of which have their best excitatory directions well within the boundaries of the response curve of GI 3. Columns a and l with best excitatory directions near the edges of the response curve of GI 3 made no detectable connection. The remaining two columns (h and m) with best excitatory directions well outside the boundaries of the response curve of GI 3 provided inhibitory input. 6. GI 3 received synaptic input from contralateral columns d, f, g, h, i, k, and m.(ABSTRACT TRUNCATED AT 400 WORDS)

Cockroaches respond to the approach of a predator by turning away and then running. Three bilateral pairs of giant interneurons are involved in determining the direction of the sensory stimulus and setting the turn direction. Each of these six interneurons has a different directional response to wind stimuli. We have tested whether these six cells use a winner-take-all mechanism to perform this directional determination: that is, each of these cells suppressing the motor response that each of the other cells promotes. Such a mechanism is found in similar behaviors of some other animals. By adding spikes to identified giant interneurons through intracellular stimulation during the sensory-induced behavior and analyzing the resulting directional leg movements, we find that a winner-take-all is not used in this system. Rather, directional determination appears to be based on collaborative calculation of direction by the giant interneurons as a group.