Neonatal hypoxia-ischemia impairs juvenile recognition memory by disrupting the maturation of prefrontal-hippocampal networks

High-prevalence/low-severity cognitive deficits represent the life-long burden of a perinatal hypoxic-ischemic (HI) insult. They have been proposed to result from dysmaturation of prelimbic-hippocampal networks, which account for mnemonic and executive performance. Already at neonatal age the communication within these networks is largely reduced after an early HI insult with mild/moderate structural outcome. However, the long-lasting consequences of the neonatal network dysfunction remain unknown. Here, we combine MRI and electrophysiology in vivo with behavioral testing to assess the effects of an early HI insult on the structure and function of prelimbic-hippocampal networks and on related cognitive abilities of juvenile rats. Despite the absence of lesions over the prelimbic cortex (PL) and hippocampus (HP), juvenile rats experiencing an early HI have lower performance in item and temporal order recognition memory. These cognitive deficits do not result from delayed somatic development or increased locomotion or anxiety. More likely, abnormal activity patterns and interactions within prelimbic-hippocampal networks account for behavioral impairment. The early HI insult causes power reduction of the fast (12-48 Hz) network activity and diminishment of neuronal firing in the PL and HP. This weaker entrainment of local circuits at juvenile age emerges in the absence of sufficiently strong directed interactions within neonatal prelimbic-hippocampal networks. Similar developmental mechanisms may account for poorer academic achievements of HI-injured infants. (C) 2015 Elsevier Inc. All rights reserved.