'Looping' - an exploration mechanism in a dark open field

The behavior of Tristram's jird (a species of gerbil) in an illuminated open field resembled that of other rodents, comprising round trips to a home base and alternating between periods of progression (locomoting and of stopping. In this study, we compared the characteristics of exploration in a dark arena with exploration by the same individuals in a lit arena. In the dark arena, stopping episodes were brief and fewer, suggesting almost continuous locomotion by the rodents. The clear distinction between progression and stopping that had characterized locomotion in an illuminated arena, thus diminished in the dark. There was also no apparent home base in the dark and traveling consisted in moving in a circular path, closing a loop to a recently traveled place that varied from one loop to the next. Locomotion in the dark may thus be regarded as a set of loops (round trips) to a continuously shifting home base, whereas with lights on the round trips converge to a home base using visible environmental landmarks. We suggest that a similar looping mechanism may be applicable to the behavior of hippocampal rats displaying hyperactivity and diversified locomotion, reminiscent of that seen in jirds in a dark arena. (c) 2004 Elsevier B.V. All rights reserved.