Motivational Systems in Muroid Rodents

The releasing stimuli of crouching and full submissive posture may include tactile stimulation of the dorsal surface of the body, which is confusing since such stimuli may also be motivating stimuli for defense and submission. This was based on the observation that a submissive animal did not usually adopt a full submissive posture until its opponent stepped onto its back in a full aggressive posture, and once the submissive animal assumed the posture he tended to maintain it for long periods of time, suggesting that the pressure of the back against the floor of the cage may have provided continual releasing stimuli to maintain the posture [Lehman and Adams, 1977]. It has been referred to as "cataleptic" immobility in R norvegicus and Me auratus [Grant and Mackintosh, 1963] and D groenlandicus [Allin and Banks, 1968]. It may also be related to the phenomenon known as "animal hypnosis" [Carli, 1977].

Motivating Stimuli of Submission

One would expect that all of the motivating stimuli of defense would also function as motivating stimuli for submission. This is the case for pain, dorsal tactile stimulation, restraint, and conditional stimuli [Lehman and Adams, 1977]. However, since many of the motivating stimuli for defense are not effective in laboratory animals due to their restricted rearing conditions, we don't yet know if sudden visual movement, sudden noise, neophobia, or defense pheromones can function as motivating stimuli for submission.

The critical motivating stimuli that activate the consociate modulator are stimuli associated with a familiar consociate opponent. Olfactory stimuli are probably the most critical ones, which may explain why muroid rodents, following damage to the olfactory system shift from submission to defense in their response to handling and conspecific social encounters. The shift in handling response is indicated by a great increase in biting which corresponds to the lunge-and-bite attack; along with an increase in other defense behaviors such as escape, it is usually referred to as the "irritability" syndrome. The extensive and complex literature on handling irritability has been reviewed elsewhere by Cain [1974] who notes that damage to brain structures involved in olfaction is more effective in producing irritability than is peripheral anosmia produced by chemical means. Biting also increases in conspecific social encounters following damage to the olfactory system in Mer unguiculatus [Hull et al, 1974] and R norvegicus [Bugbee and Eichelman, 1972] , while negative results have been reported in M musculus [Fortuna and Gandelman, 1972].

A shift from submission to defense, indicated by increased lunge-and-bite attack, is also produced by social isolation. This is consistent with the proposal that familiarity with consociate stimuli is necessary for activation of the consociate modulator and with the data (reviewed earlier regarding offense) that olfactory familiarity fades after several weeks of social isolation. The increased biting after isolation has been observed both in conspecific test situations [Hutzell and Knutson, 1972] and in response to human handling [Hatch et al, 1963; Moyer and Korn, 1965].

Another motivating stimulus of the consociate modulator may consist of the high frequency rhythmic twitches of the vibrissae of the opponent [Komisaruk, 1970] .They may function to identify the opponent as a conspecific. When these twitches are abolished by lidocaine anesthesia of the face, a rat is more likely to be bitten (ie, receive a lunge-and-bite attack) on the face during shock-induced fighting [Thor and Ghiselli, 1975; Blanchard et al, 1977b; Kanki and Adams, 1978].