Behavioural Brain Research 159 (2005) 27–36 Research report ‘Looping’—an exploration mechanism in a dark open field Pazit Zadicario 1 , Reut Avni 1 , Eyal Zadicario, David Eilam ∗ Department of Zoology, Tel-Aviv University, Klauzner St., Ramat-Aviv 69978, Israel Received 23 September 2004; accepted 29 September 2004 Available online 10 November 2004 Abstract 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. © 2004 Elsevier B.V. All rights reserved. Keywords: Exploration; Home base; Stopping behavior; Navigation; Orientation; Path integration; Visual landmarks 1. Introduction Exploration and navigation are important tools in the study of animal cognition and the underlying brain mechanisms, since these behaviors are highly structured, reflecting the ul- timate output of brain activity and integration of proximal, distal, olfactory, visual and self-generated idiothetic cues. For such research, open field is the most widely used tool in ani- mal psychology, offering a relatively simple testing environ- ment for a variety of species [49]. Numerous studies have examined behavior in the open field with lights on, when visual cues are available to provide the animal with refer- ences for navigation. With lights on, locomotor behavior of wild and laboratory rodents placed in an unfamiliar arena is organized in reference to a key location—the home base [6–8,10,11,40,41]. At this key location the rodent demon- strates typical behaviors (e.g. grooming and crouching), and ∗ Corresponding author. Tel.: +972 3 6406471; fax: +972 3 6406988. E-mail address: eilam@post.tau.ac.il (D. Eilam). 1 Equally contributed in all phases of this study. sets out on round trips in the area. These trips have a typ- ical structure of slow locomotion and frequent stops in the outward-bound journey, compared with fewer stops and faster locomotion in the homeward bound one. This spatio-temporal structure of locomotor activity was shown to withstand ex- tensive changes in the size of the environment [8]. To date, it has been unknown whether this structure of open field behav- ior with lights on is also preserved with lights off, when the animal has to navigate in total darkness and cannot rely on visible landmarks. ‘Selective’ perception may apply to land- marks, with different animals depending on different cues [1]. For example, rats have a preferred hierarchy in cue using, re- lying first on visual, then olfactory, and finally self-generated cues (path integration) [29]. For this reason, experiments on navigation and exploration try to control or isolate the role of specific sensory information. When tested in the dark, rats’ level of activity has been shown to be raised, expressed mostly in greater distance traveled. Their level of anxiety is lower and the amount of rotations (turning) is higher than in rats tested in the light [4,23,33]. Moreover, in the dark or in reduced moonlight 0166-4328/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2004.09.022