Altered pathways for auditory discrimination and recognition memory in preterm infants

Abstract

Preterm infants are at increased risk for cognitive disorders, including impairments in recognition memory. This study evaluated the effects of extreme prematurity on the neural pathway for auditory recognition memory using event‐related potentials (ERPs), a neurophysiological technique widely used in cognitive neuroscience. ERPs were recorded at term postmenstrual age in 35 preterm infants born at less than 32 weeks’gestation (22 males, 13 females; mean birthweight ([BW] 1154g, SD 374g) with normal brain ultrasounds, compared with 40 healthy, term newborns (1 to 3 days of age; 20 males, 20 females; BW 3672g, SD 420g). Because infants must be able to detect and discriminate sounds before recognizing them, two paradigms were used to assess these functions. The first evaluated the detection and discrimination of speech sounds. The second tested recognition of the mother's voice compared with a stranger's. Results showed significantly different patterns of speech sound discrimination in preterm infants compared with term infants. No evidence of maternal voice recognition was elicited from the preterm infants. No specific patterns of auditory detection or discrimination were associated with patterns of recognition memory, suggesting that the function of multiple neural pathways may have been altered in this group of preterm infants. These results provide a functional corroboration of magnetic resonance imaging studies showing effects of prematurity on early brain development, even among preterm infants with normal cranial ultrasonography.

Decreased Right Temporal Activation and Increased Interhemispheric Connectivity in Response to Speech in Preterm Infants at Term-Equivalent Age

“…In addition, a negative correlation was observed between cortical activity in response to IDS and PNA in the right temporal area (see Figure 5). This finding is consistent with previous ERP studies showing that altered neural response for processing speech sounds such as syllable or consonant changes occurs in preterm infants at term-equivalent age (Therien et al, 2004; Key et al, 2012). With the higher spatial resolution of multichannel NIRS, the present data supports these findings and suggests that increasing PNA in preterm infants was associated with decreased oxy-Hb changes with speech in the right temporal region, despite greater postnatal experience.…”

“…Preterm infants at term-equivalent age are likely to have less intrauterine auditory experience than full-term neonates. In fact, preterm infants at term exhibited no difference in ERP in response to the mother’s and strangers’ voices despite longer postnatal exposure to the maternal voice (Therien et al, 2004). …”

“…In full-term neonates, brain processing of speech stimuli varies with postnatal auditory experiences, and more exposure to familiar stimuli results in larger ERP amplitudes (Cheour et al, 2002; deRegnier et al, 2002). On the other hand, Therien et al (2004) reported that preterm infants measured at term-equivalent age exhibited different polarity and scalp distribution of ERP for speech sounds (syllable changes) compared with term infants. In addition, Key et al (2012) examined the effect of gestational and PNA on speech sound perception in preterm and full-term infants treated in the neonatal intensive care unit (NICU) using ERP.…”

Effect of mother's voice on neonatal respiratory activity and EEG delta amplitude

“…Previous studies identified these cortical regions as sensitive to the mother's voice (Beauchemin et al, 2010;Dehaene-Lambertz et al, 2010;Siddappa et al, 2004;Therien et al, 2004). Furthermore, each EEG electrode was linked to an earlobe reference electrode at A2, and these signals were sampled at 1,000 Hz and filtered with a 50-or 60-Hz notch filter to suppress noise from alternating current power sources.…”

“…Second, we needed another new measure to investigate the cortical functions related to the changes in RR. In the previous studies, slow latency components in several kinds of EEG such as Nc and PSW were measured as activities of the cortical attentional function (e.g., Richards, 2003;Siddappa et al, 2004;Therien, Worwa, Mattia, & deRegnier, 2004). These slow latency components correspond to the amplitude of EEG delta waves (.5-4 Hz).…”