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Mounting evidence shows that physical activity, social interaction and sensorimotor stimulation provided by environmental enrichment (EE) exert several neurobehavioural effects traditionally interpreted as enhancements relative to standard housing (SH) conditions. However, this evidence rather indicates that SH induces many deficits, which could be ameliorated by exposing animals to an environment vaguely mimicking some features of their wild habitat. Rearing rodents in social isolation (SI) can aggravate such deficits, which can be restored by SH or EE. It is not surprising, therefore, that most preclinical stress models have included severe and unnatural stressors to produce a stress response prominent enough to be distinguishable from SH or SI-frequently used as control groups. Although current stress models induce a stress-related phenotype, they may fail to represent the stress of our urban lifestyle characterized by SI, poor housing and working environments, sedentarism, obesity and limited access to recreational activities and exercise. In the following review, we discuss the stress of living in urban areas and how exposures to and performing activities in green environments are stress relievers. Based on the commonalities between human and animal EE, we discuss how models of housing conditions (e.g., SI-SH-EE) could be adapted to study the stress of our modern lifestyle. The housing conditions model might be easy to implement and replicate leading to more translational results. It may also contribute to accomplishing some ethical commitments by promoting the refinement of procedures to model stress, diminishing animal suffering, enhancing animal welfare and eventually reducing the number of experimental animals needed.

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To study how motivational factors modulate experience-dependent neurobehavioral plasticity, we modify a protocol of environmental enrichment (EE) in rats. We assumed that the benefits derived from EE might vary according to the level of incentive salience attributed to it. To enhance the rewarding properties of EE, access to the EE cage varied randomly from 2 to 48 h for 30 days (REE). The REE group was enriched only 50% of the time and was compared to standard housing and continuous EE (CEE) groups. As behavioral readout, we analyzed the spontaneous activity and the ultrasonic vocalizations (USVs) within the EE cage weekly, and in the open field test at the end of the experiment. In the cage, REE increased the utilization of materials, physical activity, and the rate of appetitive USVs. In the OF, the CEE-induced enhancements in novelty habituation and social signaling were equaled by the REE. At the neural level, we measured the expression of genes related to neural plasticity and epigenetic regulations in different brain regions. In the dorsal striatum and hippocampus, REE upregulated the expression of the brain-derived neurotrophic factor, its tropomyosin kinase B receptor, and the DNA methyltransferase 3A. Altogether, our results suggest that the higher activity within the cage and the augmented incentive motivation provoked by the REE boosted its neurobehavioral effects equaling or surpassing those observed in the CEE condition. As constant exposures to treatments or stimulating environments are virtually impossible for humans, restricted EE protocols would have greater translational value than traditional ones.

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Resumen La discusión en torno a la influencia del ambiente sobre la ontogenia ha alimentado la interrogante sobre cuál es el grado en el que, a través de la manipulación del contexto, se modifican las características de los individuos. Actualmente, la evidencia científica desde distintos campos (e.g., Psicología del desarrollo, Neurociencias) describe cómo el ambiente es capaz de modular los procesos del desarrollo y las distintas capacidades del cerebro, así como los mecanismos plásticos que subyacen a dicha modulación. Con base en esta evidencia, distintas aproximaciones metodológicas orientadas a la estimulación temprana (ET) se han propuesto potenciar el desarrollo o remediar problemas que se presentan durante las etapas tempranas del ciclo vital. En este contexto, se brinda una revisión del tema y se ofrece un marco teórico general sobre los antecedentes y sobre los principios que sustentan la estimulación del sistema nervioso (i.e., plasticidad cerebral). Además, a través de una aproximación empírica y un proceso de revisión bibliográfica, se presenta la evidencia disponible de algunos de los métodos de mayor conocimiento/uso en Costa Rica (i.e., Doman- Delacato, Snoezelen®, Point y Bebé Políglota). Al recapitular los alcances y las limitaciones de la ET, se concluye que es necesario sistematizar las experiencias profesionales de forma tal que permitan abrir un debate académico sobre el tema.

Abstract The discussion about environmental influence on ontogeny has fueled the question about how much context manipulation can regulate individuals' characteristics. Today, scientific evidence from different fields (e.g., developmental psychology, neuroscience) describes not only how environment can modulate brain development and function, but also the plastic mechanisms involved. In consequence, different methodological approximations of early stimulation (ES) have arisen, although they are not necessarily based on solid empirical evidence. In this context, a brief approximation to the ES background is provided, as well as a general framework about brain plasticity. In addition, the theoretical and practical perspective of the ES practitioners is also described by detailing the empirical evidence around its most known/used variants in Costa Rica (i.e., Doman-Delacato, Snoezelen®, Point and Bebé políglota). Finally, bringing up the scope and limitations of ES, we conclude that the professional experiences need to be systematized, in order to open an academic debate on the subject.

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