Auditory Evoked Potentials

Hearing loss is the most common sensory disorder in the world and can cause speech disorders in humans. The best method to solve this problem is to use electroencephalogram (EEG) for an inchoate and effective hearing screening. Auditory evoked potentials (AEPs) is a kind of EEG signal emitted from the scalp by auditory stimuli.

AEPs

Perception of sound can alter the electroencephalogram of a human listener, which is known as AEP. AEPs are produced after auditory stimulation at different levels of the auditory system. Electrocochleography is a technique for recording AEPs of the inner ear. The recording is performed using a needle electrode placed on the promontory or noninvasive with tympanic membrane or ear canal electrodes.

Depending on the incubation period, AEPs can be divided into early, middle, or late responses, which are respectively named auditory brainstem responses (ABRs), auditory middle latency responses, and auditory late-latency responses.

• ABR includes the early portion of 0-12 ms AEPs. The ABR waves or peaks are usually marked by Roman numerals I-VII. Waves I, III, and IV are generally considered to have clinical significance. ABRs are used to diagnose and locate pathology affecting brainstem pathways. Also, ABRs are widely used in hearing function test.
• Middle latency Auditory Evoked Potential (MLAEP) consists of 8-50 ms AEPs. These middle latency responses show a higher variability than the ABRs, which can be inhibited by attention regulation or anesthesia. MLAEP provides an objective assessment of a patient's auditory function, including monitoring the depth of anesthesia, locating thalamocortical lesions, and assessing the effect of electrical stimulation on cochlear implantation.
• The auditory late-latency responses, including the P50, N100, N1-P2 complex, Mismatch Negativity (MMN), and P300. The P50 is involved in sensory gating and has two main neural generators, the auditory cortex and the dorsal anterior cingulatecortex (dACC), and possibly the ventrolateral prefrontal cortex (VLPFC). The N100 is an event-related potential (ERP) component that is primarily determined by sensory processing, and it has been explicitly proposed that the primary and secondary auditory cortices are the primary neurogenerators.

Fig.1 Overview of the auditory evoked potentials, including the auditory brainstem responses (waves I-VI), the auditory middle latency responses (P0-Pb), and the auditory late-latency responses (N100-P300). (Joos, 2014)

Different Kinds of AEPs

• Obligatory cortical AEPs

The obligatory AEPs can be elicited by a variety of stimuli including clicks, tone bursts, and speech phonemes. The obligatory cortical potentials consist of a series of vertex positive and negative peaks (P1, N1, P2) that are optimally elicited by tone bursts of reasonably long duration.

• Discriminative cortical evoked potentials (MMN, P3)

When listeners are tested using the “weird” paradigm in which a frequent/standard stimulus and an infrequent/deviant stimulus are presented in the same stimulus train, the response to the infrequent stimulus was different from the response to the frequent stimulus. A “mismatch negativity” (MMN) appears as enhanced negativity in the 100-200 ms range and a P3 response occurs. MMN is elicited passively, with the listener ignoring the stimuli, whereas P3 is normally elicited using an active paradigm with the listener attending to the stimuli and responding behaviorally to the deviants.

Applications

AEPs can be used to assess auditory function from the level of the inner ear to the cortex. The middle and late cortical potentials have received considerable attention since they primarily reflect activity in the thalamus and higher auditory centers. Abnormalities of these evoked potentials are found in many diseases that affect central nervous system function, such as learning disability, schizophrenia, Alzheimer’s disease, autism, dementia HIV infection, and cortical deafness. Several studies have shown that the morphology, latency, and amplitude of cortical evoked potentials vary with auditory experience in deaf children and adults who receive cochlear implants and in normal listeners who receive auditory training.

Future research making use of AEPs could be of great interest to further unravel the fundamental neurobiological mechanisms of tinnitus and auditory perception. Creative Biolabs has a very strong technical force in the field of neuroscience research, focusing on AEPs research. We can help you better study the AEPs to reveal the basic mechanism of tinnitus and auditory perception-related neurobiological diseases. If required, please contact us for further details.

Reference

1. Joos, K. et al. From sensation to percept: the neural signature of auditory event-related potentials. Neurosci Biobehav Rev. 2014, 42: 148-56.