Heterogeneity of neuronal subserving of decision-making

Abstract

To follow the development of MEG sleep patterns and auditory evoked responses (AERs) during the first six months of life.The subjects were 18 neonates, born at conceptional age (CA) 36–42 weeks, following uncomplicated pregnancies. During each session, several 10-min MEG recordings were acquired in the presence of auditory stimulation. The recordings were classified into three distinct MEG patterns—low amplitude irregular; high-amplitude slow; and mixed—based largely on MEG amplitude and frequency. Averaged AERs were computed for the entire recording and for each MEG pattern within the recording. The results were based on analysis of 61 recording sessions of the 10 subjects who yielded three or more sessions of usable data.Developmental changes in the MEG sleep patterns were most pronounced at the earliest ages. By CA 48 weeks the patterns had progressed to a more mature form, characterized by the prevalence of delta wave sleep, absence of discontinuity, and development of spindling and higher amplitude delta rhythms. In contrast to the MEG patterns, the AERs did not change markedly during the first 8 weeks (CA 40–48 weeks) and showed a simple morphology, consisting of a prominent deflection at 250 ms (P250m) and a more diffuse one at around 750 ms (N750m). During the period CA 48–54 weeks, however, a relatively abrupt transition occurred to a more complex morphology, characterized by a double peak with peak latencies 150 ms (P150m) and 350 ms (P350m). Beyond this period the AERs continued to evolve, showing biphasic complexes and the emergence of late components arising from outside the auditory cortex.Over the age range of this study the MEG sleep patterns and AER developed in succession, rather than concurrently; i.e. development of the sleep patterns was most rapid during the first 8 weeks (CA 40–48 weeks) while major development of the AERs commenced after this time.This finding suggests that the brain must achieve a certain level of overall maturity, reflected in the character of the MEG sleep patterns at CA 48 weeks, before the cortex enters a phase of significant functional development, reflected in the more rapid evolution of the AER after CA 48 weeks. The results of this study affirm the efficacy of MEG for spatiotemporal characterization of neonatal brain activity.