Baylor College of Medicine News

Common sequences use less brain activity

If you think counting to 10 or reciting the alphabet doesn't take a lot of brain power, you¹re not entirely wrong.

Researchers at Baylor College of Medicine say these types of ordinal sequences shown in the correct order are processed differently in the brain. Not only do they stimulate less activity in comparison to sequences that were presented out of order, but also involve portions of the brain not directly related to language acquisition.

The findings appear in the open access journal Frontiers in Neuroscience.

Predictions save energy

"The amount of brain activity during the sequences shown in correct order suggests that the brain can predict what is coming up next," said Dr. David Eagleman, assistant professor of neuroscience at BCM and an author on the paper. "When an event happens, the brain can use less energy in its response if it has already predicted that event. Fundamentally, its job is to make a good model of the world so that it can avoid being surprised. The better it predicts, the more energy it saves."

Past studies have shown unique conditions related to ordinal sequences such as in some forms of dementia where memories for ordinal stimuli such as numbers are spared, while those for non-ordinal stimuli, like names, are impaired. Also, in a neurological condition called synesthesia, unrelated sensory experiences such as color are triggered by ordinal stimuli such as numbers, letters and months of the year.

Measuring brain's activity

To further investigate and measure the brain activity during these tasks, Eagleman and his colleagues used functional magnetic resonance imaging (fMRI).

Participants were presented with lists of five words that appeared one after the other for half a second each. In one condition, ordinal words were shown in their correct order (e.g. Monday, Tuesday, Wednesday, Thursday, Friday). The second condition involved ordinal words presented in a scrambled order, and the third contained words belonging to non-ordinal categories.

The researchers compared the brain scans obtained during the different trials to determine which brain regions responded to ordinal words, and how the predictability of the word sequences affected the patterns of brain activity. Scrambled sequences (such as Sunday, Wednesday, Tuesday, Friday) elicited greater activity than did sequences in their correct order.

The more predictable a sequence of ordinal words was, the less brain activity it evoked. This, the researchers say, is direct evidence that long-term experience dampens neural activity.

Surprise finding

The findings also reveal the processing of ordinal sequences involves more activity in the right hemisphere than the left--a surprise finding given that language is typically a left hemisphere phenomenon.

"We are just beginning experiments in which we teach people with synesthesia a new alphabet of arbitrary symbols--what we call an ‘alien’ alphabet. Through the use of video games, we rigorously train them on this novel sequence. We predict that the arbitrary symbols will take on synesthetic colors and that the representation of those symbols will move from the left to the right hemisphere."

In addition to Eagleman, BCM co-authors include Vani Pariyadath, Mark H Plitt and Sara J Churchill.

Funding support for this work was provided by NIH RO1 NS053960 (DME) and a Guggenheim Fellowship (DME).