Mismatched brains


In a nutshell: Investigates brain connectivity underpinning responses to surprising events in elderly people.

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Mismatched brains

Your brain is very good at picking out odd noises from a series, a skill related to its ability to shift attention to what matters most, which it does continuously, subconsciously, and at lightening speed. Just consider what happens if your smoke detector chirps, or you hear the faint screech of brakes in the distance.

This study found that the brain of an older person is less adept at picking up those odd-ball events.

The ability to spot the unusual is called (somewhat clumsily) “mismatch negativity” or MMN. It is easy to measure as changes in brain electrical activity, and is most often studied using visual and sound cues, although it also happens with smell and touch.

“It’s a really well understood network in the brain, and a good place to start when investigating how the healthy ageing brain changes over time“, says Gerald Cooray of the Karolinska Institute in Stockholm, who led the study.

When a sound is played, EEG recordings pick up cross talk between the auditory cortex (which receives sound inputs from the ears), the temporal lobes (which process sounds) and the frontal lobes (responsible for complex thought such as decision making). Odd-ball sounds in a sequence of identical tones, change the pattern and frequency of this crosstalk.

Cooray and his colleagues, including CIBF chief investigator Marta Garrido, asked men and women aged either 70 to 78 years or 20 to 35 years to press a button when they heard an odd-ball sound. At the same time, the volunteers’ brain responses were measured via EEG.

Older people had far less change in activity in the frontal lobe in response to tone changes. Similar patterns are seen in people with memory disease such as dementia.

Nonetheless, in this study, the reaction times for the older people, as measured by how fast they pressed the button, was the same as for young ‘uns. One explanation is that the brains of older people process the information as efficiently as young people, albeit it differently.

Another explanation, favoured by the body of evidence, is that the brain recordings are picking up an age-related impairment that would lead to slower reaction times to more complex surprise events.

Cooray, G., Garrido, M. I., Hyllienmark, L., & Brismar, T. (2014). A mechanistic model of mismatch negativity in the ageing brain. Clinical Neurophysiology, 125(9), 1774-1782.

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