Working memory performance assessment while monitoring the prefrontal cortex hemodynamics by means of functional near infrared spectroscopy

Abstract

One of the popular experimental paradigms for functional neuroimaging studies of working memory (WM) has been the n-back task, in which subjects were asked to monitor the identity or location of a series of verbal or nonverbal stimuli and to indicate when the currently presented stimulus is the same as the one presented n trials previously. It is known that dorsoleateral and ventrolateral prefrontal cortex (PFC) is especially active during cognitive task requiring working memory performance. Functional near-infrared spectroscopy (fNIRS) is an optical imaging method, which allows non-invasive in vivo measurements of changes in the concentration of oxygenated (HbO2) and deoxygenated (DeoxyHb) haemoglobin in cortical tissue. In this thesis fNIRS was used to determine the activity on PFC of 9 graduate student subjects, who were asked to take an n-back test involving WM load. A gamma function variate was used to model the hemodynamic response behavior during the task and statistical analysis was applied to determine parameters from the near infrared spectroscopic signals that are in correlation with the WM load. A correlation between the working memory load and hemodynamic response function parameters determined form NIRS signal, was observed on left and right channels on the forehead probe. Model applied in this thesis enabled a quantification of the WM load solely by using fNIRS as a neuroimaging device.|Keywords: Functional Near-Infrared Spectroscopy, Working Memory, n-back, Prefrontal Cortex, Gamma function, Hemodynamic Response Function.