One of the key elements of memory – how we store and retrieve words according to what they mean – has been unravelled by analysing electrical signals from people’s brains while they recalled lists of words.

Although the discovery cannot identify the individual words being filed, which could effectively make a very basic form of mind-reading possible, it does for the first time reveal the electrical circuitry vital for storing words according to what they mean, rather than where they came in a sequence, for example.

“Our main focus is on how people organise their memories,” says Jeremy Manning, currently at Princeton University. “So we looked at the degree to which people organised their memories according to the meanings of words.”

Calling Roget

The researchers recruited 46 patients with epilepsy who had already had electrodes implanted in their brains for treatment purposes. The electrodes allowed the researchers to measure electrical activity in the brain as the participants viewed lists of 15 to 20 words. A minute later, the patients were asked to recall aloud as many as possible, in any order.


Collectively, the participants viewed 1550 lists, including a total of 24,760 words. The researchers included within each list words with similar meanings or associations, such as “goose” and “duck”, to see if recall of one prompted recollection of the other.

Participants tended to recall words of similar meaning together. They also reproduced the same pattern of brain activity a second before saying the word as they did when they read the word in the list.

“Our data show how neural representations of meaning predict the way in which one item cues another during spontaneous recall,” says Michael Kahana of the University of Pennsylvania, Philadelphia, who led the research team.

By studying patterns of electrical activity at various points in the experiments, the team could work out exactly which parts of the brain are deployed while its “thesaurus” is active. The occipital lobe, usually linked with vision, appeared crucial in the brain circuitry that initially assigned meaning to words, but there was no evidence that it helped to organise the words according to those meanings: that role was apparently performed by the temporal lobe. Retrieval depended mainly on the hippocampus, already known to be crucial for memory.

Mechanistic model

Kahana hopes to perform follow-up studies. He will look at the brain patterns associated with memories stored according to other criteria – for instance, how big objects were, what they smelled or tasted like, or where they were geographically.

Other neuroscientists say the findings could help unravel how brain cells actually store memories. “The study is exciting because it represents a step towards more mechanistic models of how the brain stores a word-meaning concept,” says Kay Brodersen, at the Swiss Federal Institute of Research in Zurich. This, in turn, might lead to better treatments for learning disorders, he says.

Previously, researchers have successfully “mind-read” images from brain activity, as well as signals from “locked in” patients who are totally paralysed. And a team led by Tom Mitchell at Carnegie Mellon University in Pittsburgh, Pennsylvania, has successfully used fMRI scans to record patterns of brain activity unique to individual words, but the patterns have to be triggered by showing participants the words in question.

Journal reference: Journal of Neuroscience, DOI: 10.1523/jneurosci.5321-11.2012