On May 9th, 2017 we learned about

Memory management in the hippocampus helps speed up our responses to speech

“I sweep my floor with a _______.”

“He sipped soup with a _______.”

“Keep your milk in the _______.”

These aren’t tough questions. You could probably, possibly involuntarily, filled in each blank before you even got to the end of each prompt. This lightning fast response may seem perfectly reasonable, but neuroscientists wanted to know exactly how those statements can be answered so much faster than something like “She lost her favorite ______.” Thanks to some embedded electrodes, it appears that part of our speedy responses is thanks to the way our brains loop in our memories to deal with different types of queries.

There have been previous studies looking at the activity in people’s brains while they focused on different prompts and cues, but they were usually done in fMRI machines. These brain scans can reveal a lot, but since they measure oxygen levels in the brain to approximate metabolic activity, they’re not well-suited for tracking neural activity that takes place in just a few milliseconds. To better track the brain’s ‘workflow’ when pondering what is used to sweep one’s floor, a group of test subjects had electrodes inserted into their hippocampus— a small structure deep in your head that is associated with memory management, among other things.

Responses can be made faster with _________.

Participants were given a variety of prompts that were either ‘open’ or ‘closed.’ Open prompts could have more than one clear answer, with experience not necessarily making an answer clearer. These were answered much more slowly than closed prompts, where past experience pointed to one likely answer, like “broom!” Tracked electrical activity found that closed prompts were answered faster in part thanks to how memories were accessed to help formulate a response.

As a prompt was read, each recognized word was processed by language centers in the cortex, but also by the hippocampus, which started hunting for memories that related to the concepts being discussed. These memories were then compared for shared links that would help fill in the sentence, almost like a merchant’s rating system; “Sentences that talk about floors and sweeping also like: brooms!” Open prompts of course couldn’t rely on quick memory association in the same way, and had to rely more on activity elsewhere in the brain to be parsed and analyzed.

Predicted speech in other _________.

A separate study found that these time-saving mechanisms likely evolved before human speech did. Researchers were able to teach monkeys a synthetic language without real meaning to test how well they could process this speech-like stimuli. Once the monkeys were familiar with the “grammar” of their fake language, they were able to correctly predict how phrases would be completed. The same neuronal activity was seen in both monkeys and humans, suggesting that this form of mental efficiency evolved in a common ancestor, and was later leveraged by humans to help us get better at talking.

Source: Brain’s hippocampus helps fill in the blanks of language, Scienmag

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