Brain Activation and Psychophysiologic Interaction in Association with a Phonological Working Memory Task

Brain activation within, and psychophysiologic interaction between, significantly activated regions in the brain obtained from a phonological working memory experiment on a single participant were studied. Given that working memory and speech processing are key functions of human behaviour, this type of investigation is of fundamental importance to our understanding of brain-behaviour relationships. The study objectives were to determine the areas that respond significantly to a phonological working memory task and to investigate the influence of babble noise on their activation and the psychophysiologic interactions (PPI) between the source region and those activated areas. Three conditions were used during functional magnetic resonance imaging (fMRI) scans which were working memory in quiet (WMQ), working memory in noise (WMN) and listening to babble noise (N). More voxels are activated in the right temporal lobe than in the left during N condition due to the non-speech stimulus. However, a higher mean stimulus efficacy (?) of the point of maximum intensity in the left temporal lobe causes its signal intensity to be higher than in the right temporal lobe. Both the WMQ and WMN conditions resulted in similar activated regions in the brain but with a higher number of activated voxels (NOV) during WMQ for the right hemispheric areas in association with the working memory task. This is due to the sensitivity of those regions in perceiving and performing the phonological working memory task in quiet to a level that actually exceeds the activation enhancement commonly associated with the performance of working memory task in noise. This is supported by the PPI results that performing the working memory task is less influenced by noise for that particular brain region.