Aging and response regulation as revealed by functional MRI

Abstract

Response regulation involves freeing oneself from habitual reactions to produce goal-relevant behaviors. The cognitive control of which is implemented by a distributed network comprising closely interacting yet anatomically dissociable components. Much behavioral data concerning inhibitory decline in aging has been reported. Age-related changes in neural activation, in terms of volume and/or pattern of activation during response regulation, however, remain unclear. We therefore employed functional magnetic resonance imaging (fMRI) technology to study the differences in voxel activation and lateralization patterns of neural activation between middle-aged and younger adults. Twenty-six subjects belonging to two groups, specifically a younger group and a middle-aged group (the mean ages of which were 22.62 and 47.68 years respectively), were administered an experimental task developed for this study which measured response regulation. There were two conditions in this task, namely the Go and the Reverse conditions. During the Go condition, the subject was required to read the direction of arrowheads. This was followed by the Reverse condition, in which the subject was first required to identify the direction of the arrowhead and then give the opposite answer, so that an up arrow should elicit a down response, and vice versa. The experiment was performed on a 1.5-T Magnetom Vision MRI scanner (Siemens, Erlangen, Germany). A single shot, T2*-weighted gradient-echo planar imaging (EPI) sequence was used for the fMRI scans (slice thickness = 5mm, in-plane resolution = 3.3 X 3.3mm, TR/TE/θ = 3000ms/60 ms/90o ). The imaging data indicated activation of a frontal (middle frontal gyrus) and cingulate (anterior cingulate region) circuit in both groups, when subjects were engaged in response regulation. At the subcortical level, activity of the right thalamus in the younger group, and of the left lentiform nucleus in the middle-aged group, was observed. For the frontal activation, the results of the lateralization index calculation indicated that the activation of older adults was more left lateralized than that of the young, when performing the same experimental task of response regulation. The findings suggested that possible age-related differences in response regulation between the middle-aged and younger adults.