Investigation of Information Coding in Short-Term Memory

The aim of this interdisciplinary project is to understand the mechanisms of neural coding related to the maintenance and retrieval of information from memory and to find the most effective markers of memory scanning time, based on the electrophysiological (EEG) and behavioral data. In particular the researcher will focus on:

1. clarifying the role of the prefrontal structures in coordinating the performance of the whole frontoparietal network (i.e. the neural system that supports coding and maintaining information in memory);
2. gaining understanding of psychophysiological mechanism involved in the first few seconds of information maintenance;
3. understanding why the information is not disturbed, but maintained in an effective way (i.e. the time sequence is preserved);
4. finding out how aging changes this processes.

Additionally, several, more specific hypotheses, will be verified by investigating patterns of communication between brain structures, and by determining, with the use of high resolution, the distribution of time-frequencies accompanying memory processes.

According to the theory proposed by Lissman and Idiart [L&I] single elements are coded by the sequential gamma rhythm cycles present in the one theta rhythm cycle, however the exact patterns of the interactions between the different rhythms during the memory processes, which would make the verification/extension of L&I model possible, are missing. In this project we want to verify the following main hypotheses:

1. The capacity of the short-term memory (STM) depends on gamma to theta (G/Th) cycle length ratio (higher ratio translates to better memory).
2. As STM capacity diminishes with age, we postulate that similar relationship would be visible on the psychophysiological level (values of G/Th ratio will be smaller)
3. The visible decrease of STM capacity as well as G/Th ratio may be manipulated by cognitive training.

The important goal of the project would be to confirm whether the limitations in the STM may be overcome by emitting signals from the prefrontal to the parietal cortex. The strength of this modulation related to control mechanisms, may be crucial for the explanation of individual differences in memory capacity.

The plan of the experiment will include: investigation of the spontaneous EEG and EEG during standard Sternberg procedure (in order to assess the memory scanning time on the behavioral level). Additionally, several behavioral test will be used to obtain the best possible estimation of participants STM: 1) the estimation of verbal STM capacity will be based on modified version of the Digit Span Task from the Wechsler battery, 2) the task concerning measurement of the working memory capacity will be used to assess the so-called operational span. The next step will include training of working memory with dual n-back procedure and recurrent behavioral tests and an EEG measurement and analysis. Attainment of the planned goals will be possible thanks to the application of the advanced signal processing techniques, which will increase the precision of the determination of the relations between the rhythms. Until now, the relationship between the theta and gamma rhythms, in the context of L&I theory, have been found by filtering EEG in frequency bands of interests or by means of the Fourier analysis. We propose to introduce the most advanced method of time-frequency signal analysis, the Matching Pursuit, which provides the highest available time frequency resolution. A dynamic interaction between the brain structures will be evaluated by means of the Short-time Directed Transfer Function, which is a very robust method with respect to noise and volume conduction and has proved to be an effective method in the investigation of cognitive processes.

Results of this project will bring substantial scientific progress in the understanding of the basic academic problem concerning psychophysiological mechanisms of coding and retrieval of the memory patterns. The planned investigations are typically interdisciplinary, which is aligned with a gold standard of brain-behavior studies, and include the following disciplines: neurophysiology, psychology, neuroinformatics and biomedical engineering.

The interdisciplinary approach will stimulate popularization of the cutting-edge approach to biological signal processing and will contribute to the dissemination of the advanced methods of neuroinformatics in the field of biological sciences. With the rapidly aging world population, understanding the mechanisms behind waning memory in older age is of great societal importance. The project offers not only possible explanations of crucial processes involved in the age-related cognitive decline but also, and more importantly, it could enable implementation of methods counteracting the undesired effects related to the deterioration of memory, thus bringing the substantial progress in the quality of life in older age.