Functional Connectivity Assessment for Episodic Memory by Decoding Theta Wave

Functional Connectivity Assessment for Episodic Memory by Decoding Theta Wave

Mallampalli Kapardi (Department of Biomedical Engineering, SSN College of Engineering, Chennai, India) and Kavitha Anandan (Centre for Healthcare Technologies, Department of Biomedical Engineering, SSN College of Engineering, Chennai, India)
DOI: 10.4018/IJCINI.2018040102

Abstract

Autobiographical events help us to analyse our own thoughts and behaviour over a period of time. Analysing the retrieval of memory helps in better understanding of the disorders. This article aims at analysing the functional connectivity of young adults during a multiphase memory retrieval process. Subjects have been made to recall events in different phases of their life. EEG signals have been recorded while the subjects are performing their tasks. Inter-hemispherical coherence has been estimated from the processed EEG signals As theta band posed higher power compared to all other bands, it was considered for further analysis. A mathematical function was formed for the processed theta wave, to determine the coherence between various electrodes. The function generated a theta wave for every task and each wave was significant in its own way. The connectivity matrix was found to identify the active electrodes during retrieval of events. The results were validated by computing coherence separately for the same electrodes and for the same events.
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1. Introduction

Memory is our ability to encode, store, retain and subsequently recall information and past experiences in the human brain. It can be thought of in general terms as the use of past experience to affect or influence current behaviour. Memory is the sum total of what we remember, and gives us the capability to learn and adapt from previous experiences as well as to build relationships. It is the ability to remember past experiences, and the power or process of recalling previously learned facts, experiences, impressions, skills and habits (Aizenstein et al., 2004). It is the storage of things learned and retained from our activity or experience, as evidenced by modification of structure or behaviour, or by recall and recognition. Current theoretical accounts of human episodic memory emphasize the subjective “re-living” that accompanies the retrieval of events (Yonelinas, 2001). These details cause a subjective sense of re-experiencing that is not present for factual or semantic knowledge, which can be accomplished in the absence of autobiographical recollection (Friston et al., 2003). On the other hand, works were also done on speech imagery, where the brain connectivity parameters were found out and analysed (Kavitha & Sandhya, 2015). In addition to them blind source separation techniques such as independent components analysis and partial least squares were also implemented (Krakow & Fish, 1998).

These methods support the estimation of signal space topography, but not provide a measure of connectivity between specific pairs of nodes, and therefore lie outside the scope of this paper (Cabeza, Kapur, & Craik, 2000). Structural MRI can be used to examine the extent and location of brain lesions, so that behavioural abnormalities observed can be directly linked to specific brain structures (Ashburner & Friston, 1999). High-resolution fMRI can help locate and assess the functionality of large neural networks so that these regions can be further studied using more traditional electrophysiological recording devices (Backman et al., 1997). Generally, psychological studies utilize EEG to study the brain processes underlying attention, learning and memory. Hence this is an approach to bridge the data acquired to map and analyse the connectivity between various regions involved during the retrieval process, (Bamford, Murray, & Willshaw, 2010) but mapping of regions for various emotion based events has not been significantly established.

The clinical applications of neurophysiologic assessments of neuropsychiatric disorders is a field that remains in its formative stages, with yet to be developed guidelines for standards for recording, indications for obtaining a particular test, and the implications of the test results. Episodic memory is related to but distinct from learning, which is the process by which we acquire knowledge of the world and modify our subsequent behaviour (Basar, Karakas, & Schürmann, 2001). The hurdle to analyse the involvement of regions of brain during retrieval of events can be overcome by implementing the application of cognitive informatics, for example, during learning, neurons that fire together to produce a particular experience is altered so that they have a tendency to fire together again. The phenomena can be explained by the fact that, a new language is learnt by studying it, but can be spoken by using the memory to retrieve the words that have been learnt.

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