Brain activation during autobiographical memory retrieval with special reference to default mode network

Abstract

Recent neuroimaging studies have suggested that brain regions activated during retrieval of autobiographical memory (ABM) overlap with the default mode network (DMN), which shows greater activation during rest than cognitively demanding tasks and is considered to be involved in self-referential processing. However, detailed overlap and segregation between ABM and DMN remain unclear. This fMRI study focuses first on revealing components of the DMN which are related to ABM and those which are unrelated to ABM, and second on extracting the neural bases which are specifically devoted to ABM. Brain activities relative to rest during three tasks matched in task difficulty assessed by reaction time were investigated by fMRI; category cued recall from ABM, category cued recall from semantic memory, and number counting task. We delineated the overlap between the regions that showed less activation during semantic memory and number counting relative to rest, which correspond to the DMN, and the areas that showed greater or less activation during ABM relative to rest. ABM-specific activation was defined as the overlap between the contrast of ABM versus rest and the contrast of ABM versus semantic memory. The fMRI results showed that greater activation as well as less activation during ABM relative to rest overlapped considerably with the DMN, indicating that the DMN is segregated to the regions which are functionally related to ABM and the regions which are unrelated to ABM. ABM-specific activation was observed in the left-lateralized brain regions and most of them fell within the DMN.

Keywords: Autobiographical memory; default mode network; functional MRI.; semantic memory.

Fig. (1)

Regions which showed greater activation during ABM relative to rest, semantic memory and number counting, superimposed on the axial images of the MNI T1 template. SEM = semantic memory; REST = rest. NC = number counting.

Fig. (2)

Regions which showed less activation during ABM, semantic memory and number counting, superimposed on the axial images of the MNI T1 template.

Fig. (3)

Regions which showed greater/less activation during ABM in relation to the DMN, superimposed on the axial images of the MNI T1 template. red = ABM > REST; blue = ABM < REST; green = SEM < REST or NC < REST; yellow = overlap between ABM > REST and SEM < REST or that between ABM > REST and NC < REST; light blue = overlap between ABM < REST and SEM < REST or that between ABM < REST and NC < REST.

Fig. (4)

The overlap of the contrast of ABM > REST and the contrast of ABM > SEM, superimposed on the axial images of the MNI T1 template. FPC, frontopolar cortex; DPM, dorsal premotor area; IPL, inferior parietal lobule; MTG, middle temporal gyrus; RS, retrosplenial cortex; PCG, posterior cingulate gyrus; STG, superior temporal gyrus; and VMPFC, ventro-medial prefrontal cortex.

Fig. (5)

The contrast effect of each task condition (ABM, SEM, and NC) compared to REST in the local maxima for the overlap between AMB > REST and ABM > SEM, which correspond to the intersection of lines in the lower panels. Bars represent the limit of the 90% confidence interval around the mean. DPM, dorsal premotor area; IPL, inferior parietal lobule; MTG, middle temporal gyrus; RS, retrosplenial cortex; PCG, posterior cingulate gyrus; and VMPFC, ventro-medial prefrontal cortex.