Hanani Abdul Manan

Early and Late Shift of Brain Laterality in STG, HG, and Cerebellum with Normal Aging during a Short-Term Memory Task

Evidence suggests that cognitive performance deteriorates in noisy backgrounds and the problems are more pronounced in older people due to brain deficits and changes. The present study used functional MRI (fMRI) to investigate the neural correlates of this phenomenon during short-term memory using a forward repeat task performed in quiet (STMQ) and in noise: 5-dB SNR (STMN) on four groups of participants of different ages. The performance of short-term memory tasks was measured behaviourally. No significant difference was found across age groups in STMQ. However, older adults (50–65 year olds) performed relatively poorly on the STMN. fMRI results on the laterality index indicate changes in hemispheric laterality in the superior temporal gyrus (STG), Heschls gyrus (HG), and cerebellum, and a leftward asymmetry in younger participants which changes to a more rightward asymmetry in older participants. The results also indicate that the onset of the laterality shift varies from one brain region to another. STG and HG show a late shift while the cerebellum shows an earlier shift. The results also reveal that noise influences this shifting. Finally, the results support the hypothesis that functional networks that underlie STG, HG, and cerebellum undergo reorganization to compensate for the neural deficit/cognitive decline.

Effects of Aging and Background Babble Noise on Speech Perception Processing: An fMRI Study

Speech perception processing in a noisy environment is subjected to age-related decline. We used functional magnetic resonance imaging (fMRI) to examine cortical activation associated with such processing across four groups of participants with age ranges of 23–29, 30–37, 41–47 and 50–65 years old. All participants performed a forward repeat task in quiet environment (SQ) and in the presence of multi-talker babble noise (SN; 5-dB signal-to-noise ratio, SNR). Behavioral test results demonstrated a decrease in the performance accuracy associated with increasing age for both SQ and SN. However, a significant difference in the performance accuracy between these conditions could only be seen among the elderly (60–65 years old) subjects. The fMRI results across the four age groups showed a nearly similar pattern of brain activation in the auditory, speech, and attention areas during SQ and SN. Comparisons between SQ and SN demonstrated significantly lower brain activation in the left precentral gyrus, left postcentral gyrus, left Heschly’s gyrus, and right middle temporal gyrus under the latter condition. Other activated brain areas showed no significant differences in brain activation between SQ and SN. The decreases in cortical activation in the activated regions positively correlated with the decrease in the behavioral performance across age groups. These findings are discussed based on a dedifferentiation hypothesis that states that increased brain activation among older participants, as compared to young participants, is due to the age-related deficits in neural communication.

Modeling Brain Responses in an Arithmetic Working Memory Task

Functional magnetic resonance imaging (fMRI) was used to investigate brain responses due to arithmetic working memory. Nine healthy young male subjects were given simple addition and subtraction instructions in noise and in quiet. The general linear model (GLM) and random field theory (RFT) were implemented in modelling the activation. The results showed that addition and subtraction evoked bilateral activation in Heschl’s gyrus (HG), superior temporal gyrus (STG), inferior frontal gyrus (IFG), supramarginal gyrus (SG) and precentral gyrus (PCG). The HG, STG, SG and PCG activate higher number of voxels in noise as compared to in quiet for addition and subtraction except for IFG that showed otherwise. The percentage of signal change (PSC) in all areas is higher in quiet as compared to in noise. Surprisingly addition (not subtraction) exhibits stronger activation.