Relative Maturation of Peripheral and Central Regions of the Human Brainstem From Preterm to Term and the Influence of Preterm Birth

Abstract

Relative maturation of peripheral and central regions of the neonatal brainstem was studied using brainstem auditory evoked responses in 174 healthy preterm infants (gestational age 30 -36 wk). From 30-to 42-wk postconceptional age (PCA), I-III and III-V intervals shortened with increasing age. It was difficult to detect any apparent differences in maturational rate between the two intervals. However, III-V/I-III interval ratio decreased with increasing age, indicating that from preterm to term III-V interval shortens more than I-III interval. During term period (37-to 42-wk PCA), I-III interval was similar to term controls, but III-V interval was significantly longer and III-V/I-III interval ratio was significantly greater than controls at 37-to 38-wk PCA and 39 -40 wk PCA and was the same as controls at 41-42 wk. Therefore, from 30-to 42-wk PCA maturation of central regions of the brainstem, reflected by III-V interval, is relatively faster than peripheral regions, reflected by I-III interval which seems to be already more mature than III-V interval before 30 wk. Maturation in central regions in preterm infants is relatively delayed at early term, but "catches-up" later, whereas peripheral regions already reach normal level of maturation at early term. Preterm birth slightly delays early maturation of central brainstem regions. . Previous studies have shown that the immature brainstem can be damaged by various unfavorable perinatal conditions, e.g., hypoxia-ischemia (2). Recent studies revealed that brain structure may be abnormal in preterm infants and preterm birth is associated with regional cerebral tissue reductions (3,4). It remains unclear whether the rate of maturation in the more peripheral and more central regions of the brainstem is equal or different during earlier life and what influence the preterm birth exerts on this maturation. The understanding will help improve the care and management of very young infants, particularly for those who may be at risk of developmental abnormalities.In addition to detecting auditory abnormalities, brainstem auditory evoked responses (BAERs) have been used to study functional status and maturation of the, specifically auditory, brainstem (5-7). The responses, generating from specific brainstem auditory relay nuclei, are extremely complex and are under multiple inhibiting and facilitating influences from the rest of the CNS. Maturation of the BAER is associated with myelination of axons, formation of central synaptic connections, and axonal diameter and has been found to correlate with maturation of the brainstem, as well as the auditory pathway (8 -10). During early life, the BAER undergoes tremendous maturational changes, characterized by a shortening of wave latencies and an increase in wave amplitudes of the response (11-14). Furthermore, a shortening of the intervals between BAER wave peaks (i.e., interpeak intervals) with increasing age has been well documented.In BAER wave form, wave I, III, and V, the three major and reliable waves, originate fro...

The maturational process of the auditory system in the first year of life characterized by brainstem auditory evoked potentials

“…On the other hand, the absolute latencies of waves III and V and inter-peak values I-III, III-V and I-V tended to diminish as the period increased (Tables 1 and 2), with a significant correlation for wave III (p=0.008) in P2 (p=0.015) and P3 (p=0.000), and between P2 and P3 (p=0.032); for wave V (p=0.009) in P2 (p=0.000) and P3 (0.000), and for interval I-III (p=0.006) in P3 (p=0.000), and between P2 and P3 (p=0.004), characterizing the myelinization of axons and maturation of the synaptic mechanisms at the brainstem level 8 , 11 , 15 . The absolute latency of wave III showed to be similar to that of adults, in the third period, 4.09±0.27 ms for the preterm group and 3.97±0.28 ms for the full- term group.…”

“…While III-V reflects the higher and central region, I-V encompasses the structure of both intervals 8 .…”

“…It is thus possible, through the BAEP research, to evaluate the maturation of the auditory nerve and brainstem, and verify the occurrence of an abnormal development process in preterm newborns or with risk indicators 5 , 8 , 16 . Hence, the absolute latency and the inter-peak intervals must be precisely determined for each period of development and according to the evaluation protocol utilized, since the BAEP are exogenous potentials, totally dependent on the characteristics of the stimulus utilized to evoke the response.…”

Neonatal brainstem dysfunction after preterm birth predicts behavioral inhibition

“…The ABR first appears around 30-33 weeks of gestation (Jiang, Brosi, Wu, & Wilkinson, 2009), a common age for preterm births. As ABR abnormalities quickly spontaneously recover, this period offers a sensitive window for testing premature neonates during a fundamental developmental period when myelination, axonal sprouting, and synaptic connections are still forming, influencing the integrity of the auditory pathways (Jiang et al, 2009;Krumholz, Felix, Goldstein, & McKenzie, 1985).…”

Neural conduction impairment in the auditory brainstem and the prevalence in term babies in neonatal intensive care unit

“…The I-III and III-V intervals are the earlier and later components of the I-V interval, and generally reflect neural conduction at the more peripheral (or caudal) and more central (or rostral) regions of the auditory brainstem, respectively (Jiang, 2012;Jiang et al, 2009). In our NICU term babies, while the III-V and I-V intervals were significantly increased, the I-III interval was only slightly increased at all click rates, without any statistical significance.…”