32 <strong>EURON</strong> <strong>and</strong> <strong>THEME</strong> <strong>joint</strong> <strong>meeting</strong> 2011
33 Euron <strong>PhD</strong> <strong>meeting</strong> 2010 Methodological considerations on exploration <strong>and</strong> discrimination measures of object recognition S. Akkerman 1,* , A. Blokl<strong>and</strong> 2 , O. Reneerkens 1 , N.P. van Goethem 1 , E. Bollen 1 , H.J.M. Gijselaers 1 , C.K.J. Lieben 1 , H.W.M. Steinbusch 1 , J. Prickaerts 1 1 Faculty of Health, Medicine <strong>and</strong> Life Sciences, Department of Neuroscience, School for Mental Health <strong>and</strong> Neuroscience, European Graduate School of Neuroscience (<strong>EURON</strong>), Maastricht University, The Netherl<strong>and</strong>s; 2 Faculty of Psychology <strong>and</strong> Neuroscience, Department of Neuropsychology <strong>and</strong> Psychopharmacology, European Graduate School of Neuroscience (<strong>EURON</strong>), Maastricht University,The Netherl<strong>and</strong>s. The object recognition task (ORT) is a frequently used tool in neurobiological research. In a sample trial, objects are presented to the animal. After a delay interval, one of the sample objects is replaced by a novel object in the test trial. Rats that remember the sample object(s) will spend more time exploring the novel object, compared to the sample object(s), the exploration difference is regarded to be a measure of memory. In this study, 28 ORT experiments were pooled, containing 731 male Wistar rats. We investigated the relationship between 3 commonly used measures of discrimination <strong>and</strong> how they were related to levels of exploration in the sample <strong>and</strong> test trial. In this context, the effects of training, trial duration, delay interval <strong>and</strong> the amnesic drugs MK-801 (0.125 mg/kg) <strong>and</strong> scopolamine (0.1 mg/kg) on exploration <strong>and</strong> discrimination measures were investigated. Finally, we addressed object bias <strong>and</strong> relativity of object novelty as possible factors interfering with exploration <strong>and</strong> discrimination performance. Our analysis showed that the ORT is sensitive to potential biases like stress <strong>and</strong> side0-effects of drugs. There was no indication of a relationship between the level of exploration in the sample trial <strong>and</strong> discrimination performance. On the other h<strong>and</strong>, exploration in the test trial was positively related to the absolute discrimination measure but not to the relative discrimination measures, making them more resistant to exploration biases. Interaction with objects in prior sessions (training) decreased discrimination during subsequent 24 h retention interval testing. Thus, discrimination appears to reflect a lesser degree of familiarity of the novel object relative to the more familiar sample object due to a more recent encounter with the latter, rather than true novelty per se. Taken together, our findings suggest the consideration of pre-experimental exposure to objects, habituation to treatment procedures, balancing of object presentation <strong>and</strong> the use of relative discrimination measures when using the ORT.