Cortical Auditory Evoked Potentials in 2-Year-Old Subjects

Original Researches Cortical Auditory Evoked Potentials in 2-Year-Old Subjects Inaê Costa1  http://orcid.org/0000-0002-1839-5106 Ayra Renata D'Agostini1  Jennifer Alves Sousa1  Ana Paula Ramos de Souza1  Eliara Pinto Vieira Biaggio1  1Department of Speech Pathology, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil Abstract Introduction Cortical auditory evoked potentials (CAEPs) can be used to evaluate both peripheral and cortical components of auditory function, and contribute to the assessment of functional sensitivity and auditory thresholds, especially in neonates and infants. Auditory evoked potentials reflect auditory maturity and precede the acquisition of more complex auditory and cognitive skills, and are therefore crucial for speech and language development. Objective The aim of the present study was to determine the presence, latency and amplitude of CAEP components in response to verbal stimuli in children aged 2 years old. Methods The sample consisted of 19 subjects, 10 of whom were male while 9 were female. All of the participants were 24 months old at the time of assessment. Results A total of 17 of the participants displayed all components of the CAEP. Additionally, no significant differences were observed between genders or ears in the present sample. The presence of all components of the CAEP in subjects aged 2 years old confirms the existence of a critical period for the maturation of auditory pathways in the first 2 years of life. Conclusion In the present study, in addition to the P1/N1 components, it was possible to observe the presence of the CAEP P2/N2 components in individuals aged 24 months, confirming the existence of a critical period for the maturation of the auditory pathways in the first 2 years of life. Keywords auditory perception; child; evoked potential; maturation; electrophysiology Introduction Auditory evoked potentials (AEPs) measure the electrical activity generated at several levels of the nervous system in response to acoustic stimuli.1,2 Auditory evoked potentials are classified based on their latency into the following categories: brainstem auditory evoked potentials (BAEPs) have a latency of 0 to 10 ms, and consist of short latency potentials which travel from the auditory nerves to the brainstem; Middle-Latency Auditory Evoked Potentials (MLAEPs) have a latency of 10 to 80 ms; and Long Latency Auditory Evoked Potentials (LLAEPs) occur 80 to 600 ms after exposure to the stimulus, and are generated by the bioelectrical activity of thalamocortical neurons.3 In neonates and infants, the study of AEPs contributes to the assessment of the sensitivity, maturation, and neuroplasticity of auditory pathways, consisting an important source of information on auditory processing and the potential need of sound amplification, facilitating the implementation of early intervention programs, if necessary.4-8 Cortical auditory evoked potentials (CAEPs) are long-latency responses also known as exogenous potentials, since they are determined by the physical properties of the stimulus rather than by the response of the subject. Cortical auditory evoked potentials consist of a series of waves (P1, N1, P2 and N2) of varying amplitude, latency and polarity. The waves can be either positive (P) or negative (N) and tend to occur 50 to 300 ms after the onset of the stimulus. These waves signal the arrival of the stimulus at the auditory cortex, and therefore contribute to the assessment of functional sensitivity and auditory thresholds.1 Cortical auditory evoked potentials reflect the detection of the stimulus by the auditory system. This process depends on the maturation of auditory pathways connecting peripheral structures to the auditory cortex9 and precedes the acquisition of more complex auditory and cognitive skills, and is therefore crucial for speech and language development.10 Cortical auditory evoked potentials are also considered a biomarker of auditory maturity. Exogenous potentials decrease in latency and increase in amplitude during the 1st year of life, reaching full maturity at ∼ 14 years old,5,11,12 although they may continue to change well into the 2nd decade of life.13 At birth, it is possible to detect the presence of the components P1/N1;14,15 however, the age at which the other components of the CAEP arise is not yet precisely known.16 The changes in these components are related to the age that they reflect in the maturation of the neural processes generating the response. Auditory maturation depends on several internal and external factors, including exposure to auditory stimulation, individual differences in developmental rates, as well as the integrity of the auditory system.17 There is no consensus in the literature regarding the age at which different components of LLAEPs first appear, or the age-based reference values for signal latency,17 although studies on the topic have been conducted.4,5,7-12,14,18-31 To date, no studies appear to have investigated CAEPs using verbal stimuli and the Smart EP platform (Intelligent Hearing Systems, Miami, FL, USA) in 2-year-old subjects. We hypothesized that P2 and N2 waves would be present by the age of 2 years old, since the level of myelination of the auditory cortex at this age would allow for the emergence of these components of the CAEP. The aim of the present study was to determine the presence, latency and amplitude of CAEP components in response to verbal stimuli in children aged 2 years old. Method This was a prospective, quantitative study conducted as part of a postdoctoral fellowship (PNPD-CAPES). This protocol was approved by a university research ethics committee (protocol number CAAE: 28586914.0.0000.5346.). All of the procedures were conducted in accordance with the ethical recommendations of National Health Resolution 466/2012. Researchers signed a confidentiality agreement, while the parents or guardians of the participants provided written consent to the participation of their children in the study. The sample consisted of 2-year-olds, born at term, seen at the Neonatal Auditory Screening service of a public health center, where the subjects underwent a transient otoacoustic emissions test, when they did not present a risk indicator for hearing impairment (to affirm the integrity of outer hair cells, and therefore, assure normal cochlear function) and/or Automatic Auditory Brainstem Response evaluation (hearing threshold of 35 dBnHL in both ears, confirming the integrity of auditory pathways in the brainstem, in children, present a risk indicator for hearing impairment as hyperbilirubinemia, syndromes, congenital infections and others), following the international protocol of the Joint Committee of Infant Hearing32 Data were collected at the Audiology and Electrophysiology Laboratory of the institution where the study was conduc (...truncated)