Rats’ novel object interaction as a measure of environmental familiarity

Abstract

Environmental familiarization is a learning phenomenon embedded within most tasks used to study learning and motivation. Given its prevalence there is surprisingly little systematic behavioral research on factors affecting familiarization. The six experiments reported in the present report used rats' tendency to interact more with a novel object in a familiar than in a novel environment as a measure of environmental familiarization. We found that 3 min of exposure to the environment was suffi cient to increase object interaction above unfamiliar controls even when testing occurred up to 48 h after initial exposure to the environment; 1 or 1.5 min of exposure was not suffi cient. Also, in the brief 2 min test, 10 min of environment exposure did not appear to increase object interaction above the 3-min condition. The 3-min of environment exposure was suffi cient for familiarization whether environment exposure occurred in one 3 min placement or two 1.5 min placements. Environmental familiarization as measured by object interaction was also sensitive to 'interference' manipulations. That is, a distinct object present during initial exposure to the environment produced a level of object interaction in testing comparable to an unfamiliar control. Similarly, exposure to a second distinct alternate environment immediately after, but not before, initial exposure to the test environment partially disrupted environmental familiarization. In sum, object interaction might serve as a useful measure for studying processes mediating environmental familiarity.

Object recognition testing: Methodological considerations on exploration and discrimination measures

“…On the other hand, it is also possible that discrimination ratios are not a valid estimate of memory strength, as was argued by Gaskin et al [2]. The slightly negative correlation that was observed in our study might be explained by the assumption that rats with higher e1 values spent less time familiarizing with the environment (contextual information), which has been shown to increase novelty preference [37,38]. During each trial, animals distribute their attention over the objects and the arena.…”

“…Therefore, it would be advisable to use fixed trial durations, since testing with an exploration threshold will lead to different trial durations for each animal which in turn will cause differences in context familiarization between animals. This familiarization bias [37,38] can be minimized by using a fixed trial duration that is long enough for the animals to reach reliable discrimination performance. Using our testing conditions, both T1 and T2 should last at least 60 s.…”

“…However, also minimal proximities of 1 cm [11] and 4 cm [2] have also been reported. Generally, climbing and leaning on objects is not considered to be object examination [36], although some do in fact consider this to be relevant object-directed behaviour [2,37,38].…”

Behavioral differences between late preweanling and adult female Sprague–Dawley rat exploration of animate and inanimate stimuli and food

“…Subjects were randomly selected same-sex littermates, with a maximum of two adults and two pups tested per litter (Elsner et al, 1986; Olazabal et al, 2002; Wilkinson et al, 2006). Except for animal husbandry, postnatal handling was minimal (Ader, 1968; Andrews and File, 1993; Ivanco et al, 1996; Meaney et al, 1991).…”

Behavioral and neuropharmacological characterization of nicotine as a conditional stimulus

“…Rats had previously been used in a brief drug-free study assessing whether exposure to an alternate environment proactively interfered with familiarization of a testing environment as indexed by novel object interaction (Wilkinson et al, 2006a). Rats were housed individually in clear 48.3 × 26.7 × 20.3 cm (l × w × h) polycarbonate tubs lined with aspen shavings.…”