Sensory and movement evoked EEG patterns in the preterm neonate

Abstract

Due to the similarities between EEG activity of humans during second trimester of gestation and the activity patterns of neonatal rodents, the latter became valuable model to study the mechanisms by which early patterns of activity may act as template for later-emerging functional maps [2] . In rodents, early EEG activity (Spindles Bursts [SB]) are generated within a complex neural network including the peripheral sensory organs, subcortical nuclei as well as cortical areas. In the barrel cortex, sensory evoked SB contain early gamma oscillations (EGO) that are primarily driven by rhythmic gamma excitation from the thalamus and enable precise temporal binding of the topographically aligned thalamic and cortical neurons. EGO support long-term dependent potentiation in the thalamo-cortical synapses [1] . Characteristic preterm EEG patterns of “Delta-brushes” (DBs) are spontaneous EEG activities and have been reported in the sensory cortices following sensory stimuli and spontaneous movements. Spatiotemporal analyses of the cortical auditory-evoked responses (AERs) using 32-electrode EEG recordings in healthy neonates aged 30 to 38 post-menstrual weeks (PMW) showed that AERs are characterized by a power spectrum increase at frequency bands ranging from delta to gamma on the electrodes overlaying temporal regions. Time-frequency wavelet analysis also showed that fast (alpha-gamma) oscillations co-occurred with the auditory-evoked delta wave from around 650 ms after the stimulus and lasted for nearly 700 ms. Stimulus locked averaging disclosed cortical auditory-evoked potentials (CAEP) with negative high amplitude delta waves peaking successively over middle and posterior temporal regions. Thus, auditory-evoked DBs in preterm neonates are slow delta waves nesting fast oscillations in the temporal regions and correspond to the late part of CAEPs, which is lost when using classical CAEP processing [3] . Decreasing from 30 to 38 PMW, this EEG pattern is thus associated with the prenatal development of sensory processing circuits and likely participate to the cortical maps maturation.