New study shows our working memory is even more complex than we thought

Our working memory is key to many unexpected things. E.g. Geake (2009) used the metaphor of spam filter as it helps selecting which information is noticed. There is also a direct link between the working memory – or rather not so working memory – and depression which could go either way btw. This new study shows that the underlying processes of our working memory are considerably more complex than hitherto assumed: two brain states must alternate rhythmically in order for a piece of information to be successfully maintained.

From the press release:

Working memory: maintaining new information for a short time

When we want to remember a new piece of information for a short time, for example a phone number, working memory is called upon. Different brain regions are involved in this process, including the hippocampus, which is known for its crucial role in long-term memory. The team headed by Prof Dr Nikolai Axmacher from the Institute of Cognitive Neuroscience in Bochum and Marcin Leszczynski, researcher in Bochum and at the Department of Epileptology at Bonn University, studied rhythmic activity patterns in the hippocampus while the subjects memorised sequences of numbers or faces.

Two activity states at semi-second intervals

To this end, the team worked with epilepsy patients who had electrodes implanted into the hippocampus for the purpose of surgical planning. Those electrodes enabled the researchers to measure the activity of the region embedded deeply in the brain. While the patients memorised sequences of faces or numbers, the researchers observed two activity states in the hippocampus, which alternated twice per second: an excited and a less excited state.

Seemingly simple tasks require highly complex processes

If the rhythmic pattern did not occur in the hippocampus, the patients tended to make mistakes during the task. Based on the activity patterns, the researchers were also able to estimate how many numbers or faces the test subjects could reliably memorise. “The results show that the brain performs highly complex processes even during seemingly simple tasks,” says Prof Nikolai Axmacher. “Our subjective feeling if something is simple or complex is not a reliable marker for how the brain actually solves a task.”

Abstract of the study:

Working memory (WM) maintenance is assumed to rely on a single sustained process throughout the entire maintenance period. This assumption, although fundamental, has never been tested. We used intracranial electroencephalography (EEG) recordings from the human hippocampus in two independent experiments to investigate the neural dynamics underlying WM maintenance. We observed periodic fluctuations between two different oscillatory regimes: Periods of “memory activation” were reflected by load-dependent alpha power reductions and lower levels of cross-frequency coupling (CFC). They occurred interleaved with periods characterized by load-independent high levels of alpha power and CFC. During memory activation periods, a relevant CFC parameter (load-dependent changes of the peak modulated frequency) correlated with individual WM capacity. Fluctuations between these two periods predicted successful performance and were locked to the phase of endogenous delta oscillations. These results show that hippocampal maintenance is a dynamic rather than constant process and depends critically on a hierarchy of oscillations.


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