title: How demanding is the brain on a reversal task under day and night conditions?
abstract: Reversal learning has been studied as the process of learning to inhibit previously rewarded actions. These behavioral studies are usually performed during the day, when animals are in their daily period rest. However, how day or night affects spatial reversal learning and the brain regions involved in the learning process are still unknown. We conducted two experiments using the Morris Water Maze under different light-conditions: naïve group (CN, n=8), day group (DY, n=8), control DY group (CDY, n=8) night group (NG, n=8), and control NG group (CNG, n=7). Distance covered, velocity and latencies to reach the platform were examined. After completing these tasks, cytochrome c-oxidase activity (CO) in several brain limbic system structures was compared between groups. There were no behavioral differences in the time of day when the animals were trained. However, the metabolic brain consumption was higher in rats trained in the day condition. This CO increase was supported by the prefrontal cortex, thalamus, dorsal and ventral striatum, hippocampus and entorhinal cortex, revealing their role in the performance of the spatial reversal learning task. Finally, the orbitofrontal cortex has been revealed as a key structure in reversal learning execution.
authors.affiliation: Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, UK; INEUROPA, Instituto de Neurociencias del Principado de Asturias, Spain. Electronic address: na423@cam.ac.uk.
authors.forename: N
authors.initials: N
authors.lastname: Arias
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, Cittadella Universitaria, SS554, km 4.5, 09042 Monserrato, Italy; INEUROPA, Instituto de Neurociencias del Principado de Asturias, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Fidalgo
authors.affiliation: Laboratorio de Neurociencias, Departamento de Psicología, Universidad de Oviedo, Plaza Feijoo s/n, 33003 Oviedo, Spain; INEUROPA, Instituto de Neurociencias del Principado de Asturias, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Méndez
authors.affiliation: Laboratorio de Neurociencias, Departamento de Psicología, Universidad de Oviedo, Plaza Feijoo s/n, 33003 Oviedo, Spain; INEUROPA, Instituto de Neurociencias del Principado de Asturias, Spain.
authors.forename: J L
authors.initials: JL
authors.lastname: Arias
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D003576:Electron Transport Complex IV / Q000378:metabolism; D007266:Inhibition, Psychological; D008027:Light; D008032:Limbic System / Q000502:physiology*; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D017397:Prefrontal Cortex / Q000502:physiology; D017208:Rats, Wistar; D012193:Reversal Learning / Q000187:drug effects*
chemical_list: D003576:Electron Transport Complex IV
keywords: Circadian rhythm; Cytochrome c-oxidase; Hippocampus; Prefrontal cortex; Rat; Spatial reversal task; striatum