Muscle group dependent responses to stimuli in a grasshopper model for tonic immobility

Tonic Immobility (TI) is a prolonged immobile condition exhibited by a variety of animals when exposed to certain stimuli, and is thought to be associated with a specific state of arousal. In our study, we characterize this state by using the reliably inducible TI state of the grasshopper (Hieroglyphus banian) and by monitoring abdominal pulsations and body movements in response to visual and auditory stimuli. These pulsations are present during the TI and 'awake', standing states, but not in the CO2 anesthetized state. In response to the stimuli, animals exhibited a suppression in pulsation and a startle response. The suppression of pulsation lasted longer than the duration of stimulus application. During TI, the suppression of pulsation does not habituate over time, whereas the startle response does. In response to the translating visual stimulus, the pulsations are suppressed at a certain phase independent of the time of stimulus application. Thus, we describe TI in Hieroglyphus banian as a state more similar to an 'awake' state than to an anesthetized state. During TI, the circuitry to the muscle outputs controlling the abdomen pulsation and the startle response are, at least in some part, different. The central pattern generators that maintain the abdomen pulsation receive inputs from visual and auditory pathways.