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Catching What the Brain Notices Without Trying: Understanding Mismatch Negativity (MMN)

Some brain responses require focused attention to measure — but others happen automatically, even without paying attention. Mismatch Negativity (MMN) is one such response, revealing whether the brain can detect a change in sound without the patient actively listening or responding.

What Is the MMN Test?

MMN is a "pre-attentive" cognitive evoked potential, reflecting automatic sound discrimination below conscious awareness. Like P300, it uses an "oddball paradigm" — frequent tones interspersed with occasional different ones — but here the patient doesn't need to attend at all. They can read or watch a silent video while the brain automatically registers the change, generating a distinctive negative response around 150–250 milliseconds after the odd sound.

Test Specifications

Duration: 45–60 min
Equipment: Evoked potential system with scalp electrodes, insert earphones
Preparation: Clean scalp; patient can be relaxed or distracted — active attention not required
Setting: Quiet, electrically shielded clinic room
Age Group: Infants through adults, including those unable to cooperate with attention tasks

Procedure of the Test

Scalp cleaned; electrodes attached with adhesive gel at standard positions.
Patient given a distracting, ignorable task, such as watching a silent film, to occupy attention.
Frequent standard tones played, interspersed with occasional different "deviant" tones, via insert earphones.
No active response is required from the patient.
Electrodes detect the automatic response in the 150–250 millisecond window following each deviant tone, averaged and compared to normal values.

Why Is the Test Done?

Assesses automatic auditory discrimination, independent of attention or cooperation
Useful for infants or patients unable to actively participate in cognitive testing
Evaluates suspected central auditory processing and discrimination difficulties
Isolates pre-attentive discrimination from attention-dependent processing (as in P300)

What Will the Result Show?

A waveform showing presence, latency, and amplitude of the MMN response to deviant tones, compared against expected normal values for age.

Interpretation

Normal: "MMN response present, latency and amplitude within normal limits — consistent with intact automatic discrimination."
Absent Response: "No measurable MMN response — may indicate reduced automatic discrimination; further evaluation recommended."
Delayed Latency: "Prolonged MMN latency — may suggest slowed automatic processing; correlate with history and other findings."
Reduced Amplitude: "Reduced amplitude — may indicate subtle discrimination difficulties; further assessment advised."

MMN needs specialized equipment and a quiet, shielded environment, so it's performed only at our clinic. Acoustik Hearing and Speech Clinic brings pure tone audiometry and hearing aid trials to your home across @Mumbai, @Navi Mumbai, and @Thane.

Book your pure tone audiometry and hearing aid trial at home, or schedule your MMN test at our clinic.

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