Behavioral switching in cockroaches: transformations of tactile reflexes during righting behavior

1. The cockroach Gromphadorhina portentosa, when standing still, responds to tactile stimulation of any region of the body with complex evasive postural reflexes (Fig. 4). These responses show local sign and irradiation and compromise a Sherringtonian "type reflex". A predominant feature of all these movements is ventral flexion of the body. 2. Righting behavior is evoked when the insect loses leg-to-ground conact, irrespective of its orientation to gravity. 3. Righting behavior commences with a pronounced dorsal flexion. In spite of the strong tactile input from the substrate received by the prothorax and the tip of the abdomen, ventral flexions are not evoked. Rather, the pronounced dorsal flexion continues (Fig. 7A). 4. In tethered insects, tactile stimulation of the prothorax evokes different motor outputs depending upon whether or not the legs are in contact with the substrate: with the legs in contact, each stimulus evokes a ventral flexion, and with contact removed, each stimulus evokes a dorsal flexion (Fig. 8). In ventral flexions, ventral but not dorsal motor neurons are excited; in dorsal flexions the reverse is true (Fig. 9). 5. Under special circumstances, righting behavior can occur when not preceded by loss of leg-to-substrate contact. In such instances, tactile stimulation of the prothorax evokes dorsal flexions, just as it does in normal righting. 6. Such a change of motor output for prothoracic stimulation is seen for numerous other sites of stimulation as well (Fig. 10). Since all these reflexes involve receptors and muscles located in diverse regions of the body, and all are switched simultaneously as righting begins, a widely distributed, unitary switching system for righting behavior is implicated. Several other reflexes do not switch during righting, and the functional significance of the persistence of these is discussed. 7. Two alternative models are presented, and serve as the basis for defining the minimal requirements to model behavioral switching in this system.