Brainstem Auditory Evoked Potentials
Brainstem auditory evoked potentials (BAEPs), also known as brainstem auditory evoked responses (BAERs), are small auditory evoked potentials that are recorded in response to an auditory stimulus from electrodes placed on the scalp. BAEPs reflect neuronal activity in areas including the inferior colliculus of the brainstem, the auditory nerve (cranial nerve VIII), and the cochlear nucleus. They all have a response latency of six milliseconds or less and have an amplitude of about one microvolt. It is possible to obtain a BAEP to a pure tone stimulus, but it is more effective when the auditory stimulus contains a range of frequencies in the form of a short, sharp click.
Test for BAEPs
When being tested for BAEPs, patients lie on their back in a reclining chair or bed and remain as still as possible. Electrodes on the scalp and each earlobe help record the response after a brief click or tone is transmitted through earphones. The person does not need to be awake for this test. The results of this test have been shown to (1) help diagnose nervous system problems including hearing loss, (2) determine the efficiency and health of a person’s nervous system, and (3) test hearing ability in people who cannot have their hearing tested by other means. Abnormal BAEP responses may result from but are not limited to (1) a brain injury, (2) developmental malformation(s) of the brain, (3) a brain tumor, and (4) speech disorders. The main indication to have this test performed is when an acoustic neuroma, a nonmalignant tumor of the vestibulocochlear nerve, is suspected.
Using BAEP in Research and Case Studies
Ondine’s curse—also known as congenital central hypoventilation syndrome (CCHS) or primary alveolar hypoventilation—is a respiratory disorder that is fatal if untreated. It is the failure of automatic control of ventilation (breathing) during sleep. In 1984, Long and Allen published a case report of a woman with alcoholism who was hospitalized with complications of CCHS. During her extended hospitalization, she had abnormal BAEPs in conjunction with hyperactive muscle reflexes and bilateral Babinski signs (abnormal flexion of the foot). They hypothesized that the patient’s brainstem had been poisoned by her chronic alcoholism, which may have resulted in her CCHS and abnormal BAEPs.
A recent study by Akin and colleagues (2016) investigated alterations in BAEPs in children with obesity. They tested the BAEPs in just under 100 children with an average age of 12 years old. The obese cohort contained roughly 65 children while the remaining 35 children were control subjects (within normal weight ranges). The researchers performed BAEP tests and measured the latency and amplitude of BAEP from the obese and control subjects. They found that the average latency was significantly longer in children who were obese compared to the control subjects. They also tested insulin resistance (IR), which can lead to diabetes among the obese children and split them into two separate groups, those with IR and those without IR. Performing the same tests, they found that children with IR had longer latency periods than those without IR. Thus, this suggests that BAEPs can be used to determine early subclinical auditory dysfunctions of obese children with insulin resistance (Akin et al., 2016).
Finally, Zafeiriou and colleagues (2000) hypothesized that BAEPs can be utilized in children with spastic cerebral palsy to test hearing. They tested 75 patients with cerebral palsy (CP) and found that 17 patients had abnormal BAEPs while 58 had normal BAEPs. They reported no statistical significance between genders, but the mean birth weight of those with abnormal BAEPs was significantly higher than for those with normal BAEPs. Several hypotheses have been proposed to explain the abnormal BAEP findings in those with spastic CP; however, nothing has been supportive of these results as of yet.
See also: Auditory Processing Disorder; Auditory Threshold; Inferior Colliculus; Vestibulocochlear Nerve
Akın, Onur, Mutluay Arslan, Hakan Akgün, Süleyman Tolga Yavuz, Erkan Sarı, Mehmet Emre Taşçılar, … Bülent Ünay. (2016). Visual and brainstem auditory evoked potentials in children with obesity. Brain & Development, 38(3), 310—316. Retrieved from http://ac.els-cdn.com/S0387760415002090/1-s2.0-S0387760415002090-main.pdf?_tid=1b83719e-eeb7-11e5-bed1-00000aacb35e&acdnat=1458490771_e31b3db75c76fa1e4ee340a3708132f6
Long, Kevin J., & Neil Allen. (1984). Abnormal brain-stem auditory evoked potentials following Ondine’s curse. Archives of Neurology, 41(10), 1109—1110. Retrieved from http://archneur.jamanetwork.com/article.aspx?articleid=583557
Zafeiriou, D. I., A. Andreou, & K. Karasavidou. (2000). Utility of brainstem auditory evoked potentials in children with spastic cerebral palsy. Acta Paediatrica, 89(2), 194—197.