ANALYSIS OF LOCOMOTOR-ACTIVITY IN THE RAT - PARALLELISM INDEX, A NEW MEASURE OF LOCOMOTOR EXPLORATORY PATTERN

Several measures of locomotor activity in rats, including the distance covered, movement time, speed of progression, and sinuosity showed si gnificant changes in extreme situations after prolonged preadaptation or after stimulation with IP amphetamine. The same measures, however, either did not change or poorly reflected the changes in locomotor act ivity consistent with progressive habituation in successive daily or w eekly recordings. Other movement parameters, such as the average angle of turns, did not change or changed marginally, even in extreme situa tions. A new locomotor parameter, the parallelism index, has been prop osed. It reflects the overall tendency to turn and the angular magnitu de of turns. The parallelism index is not directly dependent on the di stance covered by the animal, and seems to significantly reflect subtl e changes in the pattern of locomotor activity that is characteristic of the exploration of an unfamiliar environment compared to the locomo tor movement in frequently visited areas. A significant decrease of th e parallelism index with rime or repeated exposure to the cage indicat es that rats perform more turns, and/or more turns under larger angles , in a more familiar or a more explored environment. It is postulated that the parallelism index decreases with the familiarity of the area bring explored. (C) 1997 Elsevier Science Inc.