Experience enhances gamma oscillations and interhemispheric asymmetry in the hippocampus

Gamma oscillations are implicated in higher-order brain functions such as cognition and memory, but how an animal's experience organizes these gamma activities remains elusive. Here we show that the power of hippocampal theta-associated gamma oscillations recorded during urethane anesthesia tends to be greater in rats reared in an enriched environment than those reared in an isolated condition. This experience-dependent gamma enhancement is consistently larger in the right hippocampus across subjects, coinciding with a lateralized increase of synaptic density in the right hippocampus. Moreover, interhemispheric coherence in the enriched environment group is significantly elevated at the gamma frequency. These results suggest that enriched rearing sculpts the functional left-right asymmetry of hippocampal circuits by reorganization of synapses.