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Articles

Researchers from the Nencki Institute studied the secrets of short-term memory

Researchers at M. Nencki Institute of Experimental Biology PAS experimentally confirmed the determinants of the short-term memory capacity, crucial for the functioning of our consciousness. The Nencki Institute announced that a person can consciously simultaneously operate five to nine portions of information. During processing portions, these portions remain in short-term memory.

Polish researchers have demonstrated that short-term memory capacity may depend on two specific bands of brain electrical activity: theta and gamma waves. This hypothesis has been known for several years. Researchers from Brandeis University in the U.S. suggested it as early as1995, but the Poles were the first to experimentally confirm this hypothesis.

Experiments were conducted by the team of Prof. Andrzej Wróbel in collaboration with Dr. Aneta Brzezicka the Warsaw School of Social Sciences and Humanities, and the main originator of the idea was psychologist Jan Kamiński, doctoral student at the Nencki Institute.

As explained in the release the Nencki Institute sent, electrical signals in the brain, recorded by electroencephalography (EEG), contain waves of different frequencies, including theta waves with frequencies of 4-7 Hz, and gamma with frequencies of 25-50 Hz. For some time it has been known that these waves are associated with information encoding in the brain. It has been observed, for example, that the amplitude of theta and gamma is greater in people forced to store more information in short-term memory.

"The hypothesis formulated in 1995 (...) assumes that we are able to memorize the amount of pieces of information corresponding to the amount of gamma cycles per one theta cycle. Previous studies only indirectly supported this thesis" - said Jan Kamiński.

A piece of information is a portion of information in memory. It may be a number, letter, concept, situation, image, or smell. "When designing experiments on memory capacity we must be very careful not to allow the subject to group multiple pieces in one" - said Kamiński, and gave an example of the sequence of numbers 2, 0, 1, 1. "These four pieces can be easily grouped in a number corresponding to the current year. Instead of four pieces of information we then have only one" - he added.

Researchers indicated that EEG reading of the theta and gamma wavelengths is not easy. These waves are not directly visible on the EEG chart. Kamiński proposed a new method for their determination. Researchers asked 17 volunteers to rest with eyes closed for five minutes, and recorded the electrical activity of the brain. Then they filtered the signals and analysed are not the cycles themselves, but the correlations between them. Only on this basis they could determine the ratio of gamma and theta wavelengths and the probable capacity of verbal short-term memory.

After the relaxation phase, volunteers took a classical short-term memory capacity test. It consisted of repeated viewing of longer and longer digit strings. Each digit was presented for one second. Volunteer had to repeat the sequence from memory: in the beginning of the test a three-digit sequence, at the end of the test a nine-digit sequence. "We observed that the longer the theta cycle, the more pieces the volunteer remembered, and the longer the gamma cycle, the less the volunteer remembered. Then we determined the correlation between test results and the estimates of EEG measurements. As expected, it proved very high and confirmed the Lisman and Idiart hypothesis" - said Kamiński.

Short-term memory capacity affects the results of reasoning - the larger it is, the better the results. Researchers at the Nencki Institute in Warsaw currently conduct experiments which aim to develop the most effective training methods for short-term memory.

Research on short-term memory capacity was funded by a grant from the Ministry of Science and Higher Education.

PAP - Science and Scholarship in Poland

last modification: 2011-12-29

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Researchers from the Nencki Institute studied the secrets of short-term memory

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