ONTOGENY OF ACTION SYNTAX IN ALTRICIAL AND PRECOCIAL RODENTS - GROOMING SEQUENCES OF RAT AND GUINEA-PIG PUPS

Behavior occurs as coordinated patterns of serial order, with rules of 'action syntax'. Grooming behavior of adult rodents provides several striking examples of action syntax rules. The most stereotyped of thes e is a 'syntactic chain' pattern, which organizes up to 25 facial stro kes and licking movements into a predictable sequence. This pattern pr eviously has been found to be emitted by diverse rodent species from a ll major suborders: myomorph, sciuromorph, and caviomorph. In this stu dy, we compared the postnatal ontogeny of grooming syntax in two roden t species: rat versus guinea pig. Rats are relatively altricial at bir th, whereas guinea pigs are precocial. A day-by-day study of the fine- grain structure of sequential patterns was carried out during the firs t three weeks after birth, using slow-motion videoanalyses and a chore ographic notation system for scoring behavioral grooming sequences. Th e results showed that substantial action syntax rules exist in guinea pig grooming even on the day of birth. For guinea pigs, postnatal groo ming syntax development was limited to minor increments in the strengt h of the syntactic pattern and in postural control. By contrast, for r at pups, action syntax did not begin to appear until the second postna tal week, and developed gradually into the third week. The development of rodent syntactic patterns in both species appeared to be independe nt of the maturation of the movements that composed the pattern. Our r esults indicate that action syntax rules develop as hierarchical entit ies independent from constituent movements.