Neuroimaging studies have revealed that motor imagery (MI) shared similar neural substrates with motor execution
(ME) though there are some differences in the activation pattern. Most previous studies generally focused on voxel-wise based analysis. However, the congruence and difference in functional brain network relevant to MI and ME task has been rarely investigated. In this study, independent component analysis (ICA) was applied to characterize the functional brain networks underlying MI and ME. Results shows that the brain networks underlying MI and ME shared similar brain regions consisted of supplementary motor area (SMA), contralateral primary sensorimotor area (M1/S1), striatum, bilateral premotor area (PMA), posterior parietal lobule (PPL), and cerebellum. However, the ME task induced stronger activities in SMA-proper, bilateral M1/S1 and cerebellum while the MI task produced greater activities in preSMA, right cerebellum, bilateral PMA, parietal cortex and striatum. These findings are in accordance with the model proposed by Hikosaka (2002) that includes the parietal–prefrontal cortical loops for a spatial sequence and the motor cortical loops for a motor sequence. Moreover, the functional connectivity within the MI/ME-relevant network was evaluated using hierarchical integration that can quantify the total amount of interaction within the network and further assess the information exchanges within/between sub-networks. Results of hierarchical integration further indicate that parietalprefrontal areas contributes more to the integration of MI network than that of ME network while motor cortical areas contributes more to the integration of ME network than that of MI network.
Autobiographical memory is the ability to recollect past events from one's own life. Both emotional tone and memory
remoteness can influence autobiographical memory retrieval along the time axis of one's life. Although numerous studies
have been performed to investigate brain regions involved in retrieving processes of autobiographical memory, the effect
of emotional tone and memory age on autobiographical memory retrieval remains to be clarified. Moreover, whether the
involvement of hippocampus in consolidation of autobiographical events is time dependent or independent has been
controversial. In this study, we investigated the effect of memory remoteness (factor1: recent and remote) and emotional
valence (factor2: positive and negative) on neural correlates underlying autobiographical memory by using functional
magnetic resonance imaging (fMRI) technique. Although all four conditions activated some common regions known as
"core" regions in autobiographical memory retrieval, there are some other regions showing significantly different
activation for recent versus remote and positive versus negative memories. In particular, we found that bilateral
hippocampal regions were activated in the four conditions regardless of memory remoteness and emotional valence.
Thus, our study confirmed some findings of previous studies and provided further evidence to support the multi-trace
theory which believes that the role of hippocampus involved in autobiographical memory retrieval is time-independent
and permanent in memory consolidation.