09 January 2012

Brain Waves and the Limits of Short Term Memory

Capacity of short-term memory impacts the effects of reasoning -- the greater the capacity, the better the effects. Currently researchers conduct studies on developing the most effective ways of training short-term memory.

...In 1995 researchers from Brandeis University in Waltham suggested that the capacity of short-term memory could depend on two bands of brain's electric activity: theta and gamma waves..."The hypothesis formulated by Lisman and Idiart in 1995 assumes that we are able to memorise as many 'bites' of information, as there are gamma cycles for one theta cycle. Research to date provided only indirect support for this hypothesis," say psychologist Jan Kamiński, PhD student from the Nencki Institute... _SD
Most neurocognitivists are slowly coming around to the idea that the "language of mind" is carried via modulated brain waves. The interaction of gamma waves (30Hz and above) and theta waves (4 to 7 Hz) is a particularly intense focus of research into neurocognition.

Recent research at the Nencki Institute in Warsaw suggests that a person's crucial short term memory capacity may be limited by the number of gamma cycles which fall on each theta cycle.
A 'bite' of information refers to its portion in memory. A 'bite' may be a number, letter, idea, situation, picture or smell. "Designing experiments on the capacity of memory one needs to be very careful not to make it too easy for the subject to group many 'bites' into one," stresses Kamiński and as an example gives the following sequence of letters: 2, 0, 1, 1. "Such four 'bites' of information are easy to group into the number corresponding to current year. Instead of four bites of information we are left with just one."

Interpreting the length of theta and gamma waves from EEG recording is not easy either. These waves are not directly visible in the EEG signal. Kamiński proposed a new method of determining them. Researchers recorded brain's electric activity in seventeen volunteers resting with closed eyes for five minutes. Next they filtered the signals and analysed not the cycles themselves but their correlations. Only based on discovered correlations the ratio of the length of theta wave to gamma wave was determined and the likely capacity of verbal short-term memory was determined.

Following the EEG recording, the volunteers, were subjected to classic short-term memory capacity test. It consisted of repeated display of longer and longer sequences of numbers. Each number was presented for one second. Then volunteers had to reconstruct the sequence from memory. At first the sequence consisted of three numbers but at the end of the exam of as many as nine. "We have observed that the longer the theta cycles, the more information 'bites' the subject was able to remember; the longer the gamma cycle, the less the subject remembered. Next we determined the correlation between the results of the tests and estimates from the EEG measurements. Just as expected the correlation turned out to be very high and it confirmed the hypothesis of Lisman and Idiart," says Kamiński._SD
Article abstract...Neurobiology of Learning and Memory

A look at Beta band oscillations and alertness, by the same authors... International Journal of Psychophysiology

And then there is this research into a "master control gene" of memory which may control as many as hundreds of other genes in the brain -- particularly the hippocampus -- which provides a much lower-level glimpse into the machinery of learning and behaviour. All levels of brain function, from the molecular to the behavioural, are important -- although it can be difficult to focus on all of them at the same time.

Our unconscious minds -- including the underpinnings of our short term memories -- function on a parallel basis. Our conscious minds tend to function on a serial -- one thing at a time -- basis. Better educational methods might take those differences into account.

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