A Statistical and Motivational Analysis of the Social Behaviors of the Male Laboratory Rat
Authors: Lehman Michael N. , Adams David B. 
Published: April 2008

The behavior sequences of male rats during tests for isolation-induced fighting were analyzed by computer. All transitional dyads which were highly significant (probability less than .001 by chance) were listed in tables and categorized. Most highly significant transition dyads fell into five categories: exploration and scent-marking; grooming; defense and submission; offense, and approach and retreat. All of these categories were obtained for sequences within the home rat, within the intruder rat, and between the two rats except for the following: offense sequences were seen only in the home rat; approach and retreat sequences were seen only in interactions; and interaction sequences usually involved combinations of offense with defense or submission rather than simple offense sequences or simple defense-submission sequences. Further analysis of exploration and scent-marking dyads suggested that the various acts and postures all reflect a single underlying motivational mechanism which activates motor patterning mechanisms whose motor patterns are directed by continually changing orientation towards different objects in the environment. The ratios of obtained to expected frequency of transition from one act or posture to another were usually symmetrical and most of the possible dyads were observed in frequencies greater than expected by chance. Analysis of grooming dyads also suggested that these acts and postures reflect a single underlying motivational mechanism which activates motor patterning mechanisms through which directing stimuli orient grooming towards various parts of the animal's own body or the body of the opponent. Within self-grooming most of the possible dyads were observed at frequencies greater than expected by chance, and the transition ratios were symmetrical. It was suggested that these behaviors all facilitate the broadcast diffusion of odors from scent glands on the face, flank, and ano-genital region, that the motivational mechanism is activated by sensations arising from these glands which are differentially activated by way of other motivational mechanisms, and that self-grooming might also be characterized as "self-anointing". Offense behaviors of the home rat tended to follow an asymmetrical sequence: from sniff-dish and crawl-over-dish to repeated offensive sideways posture to full aggressive posture to bite-and-kick attack, with the latter act followed by a refractory period. The frequent initiation of the sequence by sniff-dish behavior was taken as evidence that an offense motivational mechanism is activated by comparison of strange rat odors with familiar home cage odors. A number of acts and postures were considered to be ambivalent or hybrids of motor patterns produced by patterning mechanisms simultaneously activated by offense and other motivational mechanisms. These include aggressive groom and rub (grooming and offense), crawl-under (exploration and offense), and offensive sidoeways posture, upright posture and boxing (both offense and defense). A detailed analysis of the many dyads from offense behavior to defense and submissive behaviors led to the following hypothesis. There are probably two different motivational mechanisms, defense and submission, which are activated by stimuli associated with attack by the opponent, dorsal tactile stimulation or an elevated approach. Both defense and submission are elicited by dorsal tactile stimulation and both are potentiated following subjection to attack. Defense, but not submission, may also be elicited by a high approach of the opponent. The motor patterns of defense are flight in a large enclosure, or high postures in a confined space. The high postures are usually of low intensity (sideways posture) if the motivating stimuli are of low intensity and if the motivational mechanism is not sensitized by previous attack. They are usually of high intensity (upright postures) if the motivating stimuli are of high intensity or if the motivational mechanisms has been sensitized by attack. The submissive postures may also be of low intensity (crouch) or high intensity (full submissive posture) depending upon intensity of motivating stimuli and sensitization by pain. Submission often includes the emission of a 25 kilo herz ultrasound cry which inhibits further attack by the opponent. An alternative hypothesis was considered: that submission and defense are sets of motor patterning mechanisms, each activated by a single motivation mechanism but differentiated by different releasing stimuli. In addition to the primary significant transitional dyads mediated by five motivational mechanisms, there were also many secondary and tertiary transitional dyads obtained as a result of the temporal correspondence of two different acts or postures each elicited as primary effects from another behavioral act or posture which preceded both of them. These secondary and tertiary effects, less significant than the primary effects, could be demonstrated by triangulation in flowcharts of the behaviors. Practically all of the 105 highly significant behavioral transition dyads in the tests could be explained as primary effects due to the action of only five basic motivational mechanisms and the secondary or tertiary effects based on these primary effects. The five motivational mechanisms were identified as: exploration and scent-marking; grooming, offense; defense; and submission. A model was presented which included these five motivational mechanisms, their critical stimulus inputs (motivational stimuli), the motor patterning mechanisms which they activate and which receive separate input from releasing and directing stimuli. Specific acts and postures could be understood as simple or complex combinations of motor patterns which were produced by motor patterning mechanisms activated by single or multiple combinations of motivational mechanisms.