Huan Luo’s group has recently published a paper on eLife demonstrating backward serial replay of sequentially memorized items in human subjects
Huan Luo’s group at the PKU-IDG/McGovern Institute for Brain Research, School of Psychological and Cognitive Sciences at Peking University has recently published a paper on eLife (Huang, Jia, Han & Luo, 2018) titled “Fast-backward replay of sequentially memorized items in humans”. They employed EEG recordings in combination with a temporal response function (TRF) method to examine the neural mechanism for sequence memory, and demonstrated that serially remembered items are successively reactivated during the memory maintenance period in a backward and temporally compressed manner.
Storing temporal sequences of events (i.e., sequence memory) is fundamental to many cognitive functions. Previous animal studies and computational modeling support serial reactivations during memory retention (Foster&Wilson, 2006; Jensen&Lisman, 2005). However, how the sequence order information is maintained and represented in working memory and its behavioral significance, particularly in human subjects, remains unknown.
In this EEG study, Luo’s group employed electroencephalography (EEG) in combination with a temporal response function (TRF) method (Jia et al., 2017; Liu et al., 2017) to dissociate item-specific neuronal reactivations (Figure 1). They demonstrate that serially remembered items are successively reactivated during the memory maintenance period. Most crucially and surprisingly, the sequential replay profile displays two intriguing temporal properties compared to the actual stimulus sequence. First, the item-by-item sequence reactivation is temporally compressed into a 200-400 ms window (whereas the actual stimulus sequence lasts for about 2-3 secs). Second, the replay profile is reversed in temporal order (i.e., 2-1 reactivation for a 1-2 sequence) (Figure 2). Most centrally, they further show that the backward sequential replay profile is strongly related to the recency effect. This fast-backward replay, previously revealed in rat hippocampus and demonstrated here in human cortical activities, might constitute a general neural mechanism for sequence memory and learning.
Figure 1. Experimental paradimg
Figure 2: illustration of the backward-fast replay in sequence memory
Dr. Huan Luo and Qiaoli Huang (3rd year PhD student in Luo’s group) are the co-corresponding authors. Qiaoli Huang and Jianrong Jia (5th year PhD student) are the co-first authors. This work was supported by the National Natural Science Foundation of China Grant to Dr. Huan Luo.
Huang, Q.*, Jia, J., Han, Q., Luo, H.* (2018) Fast-backward replay of sequentially memorized items in humans. eLife 7: e35164
https://elifesciences.org/articles/35164
References
1. Jia, J., Liu, L., Fang, F., and Luo, H. (2017). Sequential sampling of visual objects during sustained attention. PLoS Biol 15, e2001903.
2. Liu, L.*, Wang, F., Zhou, K., Ding, N., Luo, H. (2017) Perceptual integration rapidly activates dorsal visual pathway to guide local processing in early visual areas. PLoS Biol 15(11): e2003646.
3. Foster, D.J., and Wilson, M.A. (2006). Reverse replay of behavioural sequences in hippocampal place cells during the awake state. Nature 440, 680-683.
4. Jensen, O., and Lisman, J.E. (2005). Hippocampal sequence-encoding driven by a cortical multi-item working memory buffer. Trends Neurosci 28, 67-72.