The hippocampus might have a much more central role to play in language and speech than we’ve ever suspected, a team of US neuroscientists claims. They examined what happens in people’s brains when they finish someone else’s sentence.

Image credits Isa Karakus / Pixabay.

Do you ever get that urge to blurt out the last word of somebody else’s sentence? Happens to me all the time. And it seems scientists do it too because a team led by senior researcher at the Donders Centre for Cognition and Radboud University Medical Centre Vitoria Piai looked into the brains of 12 epileptic patients to make heads and tails of the habit. What they’ve found flies against everything we currently know about how memory and language interact in our brains.

The 12 patients were taking part in a separate study trying to understand their unique patterns of brain activity. Each one of their brains was monitored with a set of electrodes. Piai and her team told the participants a series of six-syllable (but incomplete) sentences, “she came in here with the…” or “he locked the door with the…” for example. After the sentence was read out to them the researchers held up a card with the answer printed on it, all the while monitoring how the patients’ hippocampi — on their non-epileptic side of the brain — responded.

When the missing word was obvious, ten out of the twelve subjects showed bursts of synchronised theta waves in the hippocampus, a process indicative of memory association.

“The hippocampus started building up rhythmic theta activity that is linked to memory access and memory processing,” said Robert Knight from the Department of Psychology, Helen Wills Neuroscience Institute, University of California, Berkeley and co-author of the paper.

But when the answer wasn’t so straightforward, their hippocampi ramped up even more as it tried (without success) to find the correct word — like an engine revving up with the clutched pulled down.

The original auto correct

“[The results] showed that when you record directly from the human hippocampal region, as the sentence becomes more constraining, the hippocampus becomes more active, basically predicting what is going to happen.”

Just like the auto correct feature replaces a more unusual word the first time you use it but adapts over time to not only stop replacing it, but also starts filling it in for you, the findings suggest that our minds try to fill blanks in dialogue drawing from our memory stores of language and the interlocutor’s particularities of speech, linking memory and language.

“Despite the fact that the hippocampal area of the medial part of the temporal lobe is well known to be linked to spatial and verbal memory in humans, the two fields have been like ships running in the fog, unaware that the other ship is there,” Knight added.

This would mean that the hippocampus plays a much more important role in language, previously thought to be the domain of the cortex — though right now, the team doesn’t know exactly how this link works. Because of this, the team hopes to continue their work to better understand the bridge between memory and language, which will hopefully give us a better understanding of the brain itself.

Another implication would be that, because at least part of the act of speaking is handled by the hippocampus and not the cortex, language might not be so human-only as we’d like to believe.

The full paper “Direct brain recordings reveal hippocampal rhythm underpinnings of language processing” has been published in the journal PNAS.