A BRAIN CRYING OUT LOUD FOR PLAY

Abstract

Play is important for an optimal development in childhood, yet how it shapes the development of the prefrontal cortex (PFC) is not fully understood. Social play behavior, the most common type of play in mammals, is critical for the development of the brain. We have previously observed that GABAergic synapses onto layer 5 neurons in the adult medial prefrontal cortex (mPFC) are reduced when rats are subject to juvenile social play deprivation (SPD). In addition, we found indications that reward processing may be altered in SPD rats. We have therefore assessed how social play shapes the orbitofrontal cortex (OFC), a region of the PFC known to be involved in processing stimulus-reward association. This region is next to the mPFC, but appears to follow a different developmental trajectory. Given that the OFC mediates reward-processing behavior, we hypothesized a significant reduction of the inhibitory synaptic activity following SPD. We made use of juvenile rats that had been subject to SPD during a critical period followed by resocialization. This allowed us to perform an immunohistochemical study to quantify the perisomatic inhibition and determine if there was a change following SPD. Surprisingly, our results did not show relevant alterations when both hemispheres were taken together, nonetheless, when the hemispheres were assessed separately, we found altered inhibitory synapse asymmetry in terms of size and intensity for all immunohistochemical markers. This study not only shows the relevance of social play for the proper development of reward- and decision-related structures, but also, for the first time, the crucial role it takes in the development of the hemisphere asymmetry.