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Updated: Aug 10, 2026
Infant Auditory Processing and Event-related Brain Oscillations
Published on: July 1, 2015
Brainstem auditory evoked response at five years and prenatal and postnatal blood lead
S J Rothenberg1, A Poblano, L Schnaas
1Center for Research in Population Health, National Institute of Public Health, Cuernavaca, Morelos CP62508, Mexico. drlead@gte.net
Insights
Prenatal lead exposure impacts children's auditory brainstem pathways. Higher maternal lead levels initially shortened brainstem auditory evoked response (BAER) intervals, then lengthened them, suggesting permanent neurotoxic effects.
Area of Science:
- Neuroscience
- Environmental Health
- Developmental Pediatrics
Background:
- Previous research linked maternal lead exposure to altered infant auditory brainstem function.
- The long-term effects of prenatal lead exposure on auditory pathways in children were not fully understood.
Purpose of the Study:
- To investigate the association between prenatal lead exposure and auditory brainstem function in children aged 5-7 years.
- To determine if early lead exposure effects on the brainstem auditory evoked response (BAER) persist into later childhood.
Main Methods:
- Brainstem auditory evoked response (BAER) measurements were taken in children aged 5-7 years.
- Maternal blood lead levels from early pregnancy were analyzed in relation to BAER interpeak intervals (I-V and III-V).
- Multiple regression models controlled for confounding factors like head circumference, age, and sex.
Main Results:
- Maternal blood lead level at 20 weeks of pregnancy was significantly associated with I-V and III-V interpeak intervals.
- A nonlinear relationship was observed: intervals decreased with lead levels up to 8 microg/dl and increased thereafter.
- Prenatal lead exposure was associated with reduced head circumference, supporting a pathway length effect.
Conclusions:
- Prenatal lead exposure has lasting effects on the auditory brainstem, indicated by altered BAER intervals at 5-7 years.
- The nonlinear effects suggest complex neurotoxic mechanisms, including impacts on pathway length and synaptic function.
- Findings suggest that lead-induced auditory brainstem alterations may be permanent.
Abstract:
Previous work from this laboratory demonstrated an association between higher maternal blood lead level at 20 weeks of pregnancy and increased I-V and III-V interpeak intervals in the brainstem auditory evoked response (BAER) recorded in 1-month-old infants. We repeated the BAER measurements with a larger group of children (n = 100-113) from the same study at 5-7 years. Maternal blood lead level at 20 weeks of pregnancy (geometric mean = 7.7 microg/dl; range 1-30. 5 microg/dl) was the only prenatal blood lead level significantly associated with I-V and III-V interpeak interval in a multiple regression model controlling for head circumference and age at time of testing and sex. In contrast to the findings at 1 month of age, interpeak intervals decreased as a linear function of increasing 20-week maternal blood lead. A nonlinear, orthogonal, second-order polynomial model was a significantly better fit to the data than the linear model. The nonlinear model showed I-V and III-V interpeak intervals decreased as blood lead rose from 1 to 8 microg/dl, and then increased as blood lead rose from 8 to 30.5 microg/dl. We hypothesized that the negative linear term was related to lead effect on brainstem auditory pathway length, and that the positive quadratic term was related to neurotoxic lead effect on synaptic transmission or conduction velocity. We found support for the brainstem length interpretation in the data, showing that 6-year-old head circumference in these children significantly decreased with increased maternal 20-week blood lead level. Increasing postnatal blood lead at 12 and 48 months was related only to decreased BAER conduction intervals across the entire blood lead range, suggesting only pathway length effects. Alterations in BAER at this age may indicate that the effect of prenatal lead exposure on the auditory brainstem is permanent, as response latencies reach essentially adult values by 4 years of age.
