Alterations in Mesoscopic Oscillations affecting Episodic Memory following Developmental Traumatic Brain Injury

Abstract

Certain deficits of episodic memory among young adults are the delayed consequences of an earlier mild or moderate Traumatic Brain Injury (mTBI). We examined alterations in hippocampal Local Field Oscillations (LFOs) of equivalently-impaired juvenile rodents to identify reliable functional markers of single-incidence mTBI. Two persistent, behavior-dependent, electrophysiological markers of injury were identified in the absence of external physiological symptoms by the analysis of wirelessly-transmitted hippocampal LFOs (3–80Hz) during repeat measures of the Novel Object Recognition (NOR) paradigm. Using a new method for detecting functional network activity at a single recording site, we correlated instantaneous increases in theta frequency and gamma magnitude with injury during periods of functional network organization and dissolution, presented here as Theta Epochs (TEs) and Theta Non-Epochs (TNEs), respectively. We estimated the efficacy of networks across pairs of such sites using new metrics such as the Coherence of Theta Phase (PCOH) and Inter-Epoch Intervals (IEIs) and demonstrated that behavioral deficits observed during the NOR testing stage correspond to electrophysiological deficits recorded during the preceding NOR familiarization stage. Increased theta frequency during TNEs and increased smoothness of PCOH during TEs were found to be robust markers of injury during memory-reliant behaviors.