Invited Lecture 2.5

Abstract

Neuroscience is an important field that explains how and why human brain executes its cognitive functions such as working memory (WM). Many WM studies were conducted using the non-invasive functional magnetic resonance imaging (fMRI). In this work, fMRI was used to investigate stochastic resonance (SR) phenomenon in an auditory WM (AWM) experiment. A backward word recall test (BWRT)  was undertaken by the participants during the execution of silent fMRI in the presence of flowing water (FW) or white noise (WN) as background. During the experiment, the 2-s EPI scans were continuously and sparsely executed with an interval of 8 s. In this 8-s interval, baseline (or quiet background with no stimulus given and no scanner sound) is alternated with 4-s stimulus presentation (AWM stimulus in the form of BWRT) embedded in the presence of backgrounds. There are four intensity levels used in this experiment; 45 dB, 50 dB, 55 dB and 60 dB. The stimulus presentation was followed by a 4-s interval for the participant to respond by recalling and producing words in a backward manner. A total of 39 subjects were scanned and two regions of interest were selected which were the bilateral primary auditory cortices (PAC). The quantities of interest are the number of activated voxels (NAV) and the percentage of signal change (PSC) within the bilateral PAC. The average NAV and PSC for the left and right hemisphere PAC over 39 subjects point to the existence of SR phenomenon that occurred in the presence of FW and WN during AWM task at a sub-optimal intensity level of 55 dB. The measurable increase in NAV and PSC is believed to be caused by moderate brain arousal (MBA) that considers the SR phenomenon when the AWM task was executed by the subject in the presence of both backgrounds.