Otoacoustic Emissions (OAEs): A Symphony from Within

OAEs test in a baby

Otoacoustic emissions (OAEs), those delicate whispers from the inner ear, hold secrets about our auditory health. Let’s delve into this fascinating phenomenon and explore its significance.

What Are Otoacoustic Emissions?

1. Definition: Otoacoustic emissions are sounds generated within the cochlea, that intricate spiral-shaped structure nestled deep in our ears. These emissions occur when the outer hair cells within the cochlea respond energetically to external sounds.

2. Discovery: The existence of OAEs was predicted by Austrian astrophysicist Thomas Gold in 1948. However, it was British physicist David Kemp who first demonstrated their presence experimentally in 19781.

3. Types of OAEs:

• Spontaneous OAEs (SOAEs): These ethereal sounds emerge without any external nudging. Imagine tiny musical notes spontaneously dancing within your ear canal. Approximately 35–50% of people harbor at least one SOAE, often blissfully unaware of their melodious companions. However, for a select few (1–9%), SOAEs manifest as an annoying tinnitus1.

• Evoked OAEs (EOAEs): These require a gentle coaxing—a stimulus to awaken them. EOAEs come in three flavors:

• Stimulus-frequency OAEs (SFOAEs): Measured during pure-tone stimulation, they reveal the cochlea’s responsiveness.

• Transient-evoked OAEs (TEOAEs): Triggered by clicks or brief tonebursts, they span the frequency range up to 4 kHz.

• Distortion-product OAEs (DPOAEs): These arise from a pair of primary tones, producing responses at mathematically related frequencies. The “cubic” distortion tone (used for hearing screening) and the “quadratic” distortion tone are the stars of this show1.

The Mechanism Behind OAEs

• Cochlear Amplification: OAEs are closely linked to the cochlear amplifier’s function. When external sounds are absent, the cochlear amplifier revs up, leading to sound production. Outer hair cells act as the energy sources for this amplification, enhancing cochlear sensitivity and frequency selectivity.

Clinical Applications

1. Inner Ear Health: OAEs serve as a litmus test for inner ear well-being. If OAEs vanish, it’s a sign that the inner ear has suffered damage.

2. Hearing Screening: EOAEs, especially DPOAEs, play a crucial role in newborn hearing screenings.

3. Diagnostic Audiology: OAE testing aids in diagnosing hearing impairments and monitoring cochlear function.

Conclusion

Otoacoustic emissions—these delicate echoes from our cochlea—remind us that our ears are not just passive listeners; they’re vibrant performers in an intricate symphony of sound.

So next time you hear a faint melody within, perhaps it’s your own inner orchestra tuning up, playing the music of life. 🎵👂🌟