Developmental Research
Processing Time and the Mismatch Negativity Test (MMN)
Our brains are designed to recognize patterns in time, like the beat of a song or the hum of a motor. When patterns change, our brains recognize that something unexpected has happened and become more active. One of the ways to measure the ability of the brain to identify unexpected changes is called Mismatch Negativity or MMN. The MMN test is a recording of brainwaves, called an electroencephalogram or EEG. During this test a recording of pure tones are played through speakers at a volume of approximately 65dB, about the same volume as normal street traffic. These tones will occur every 500 milliseconds. Once in a while, the tone will occur before 500 milliseconds have passed. We record brain waves to determine if the brain noticed that the sound came a little bit early. We are interested in how well babies of different ages sense a change in the time pattern of the sounds and what influences, such as genetics and exposure to tobacco, affect this ability.
The test begins with a thorough cleaning of the areas where we will be attaching the electrodes. In order to achieve a good connection, a gentle exfoliant is used to remove dead skin, followed by a gentle scrubbing with an alcohol preparation pad that is designed to remove any excess exfoliant. A small cap, similar to a baby bonnet, is placed on the infant’s head. This cap contains electrodes that can sense brain activity. These electrodes don’t hurt the child at all, but allow us to record the infant's brain waves. The electrodes are held in place with a type of paste that is used on human skin and paper tape. The electrodes are designed to monitor the electrical currents in the brain and the muscle activity around the eyes. Since we would like the infant to sleep during this test, we try to schedule the appointment to coincide with the infant's naptime. While the baby sleeps, we play tones, which are no louder than street traffic, through speakers behind the infants head. We record the infant's brain waves as long as we are able (usually until the baby wakes up).
Cleaning the infant’s skin and attaching the cap takes roughly 30 minutes, and the recording takes approximately 45 minutes. The entire session time lasts approximately 1 ½ to 2 hours in duration. At the first visit we also review the consent forms and obtain demographic information, which usually takes about 30 to 45 minutes, so if the MMN is your first visit please plan on being at the lab for about 2 ½ hours. As a thank you for participating, parents are compensated for their time.
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