Discovery the Neuronal Populations Controlling Memory Update
The research group led by Assistant Prof. Akinobu Suzuki and Distinguished Prof. Kaoru Inokuchi at the Department of Biochemistry, Graduate School of Medicine, University of Toyama, has discovered in mice neuronal populations in the posterior parietal cortex (PPC), a region of the cerebral cortex, that refer to past and present information and update memories.
Background and overview
When we process information from a new experience, we compare it to our memory of the relevant past experience. Then, by connecting the new information to the past memories, the past memories are updated. In this way, memories are updated in their semantic representation by new experiences, allowing us to form new knowledge and adapt to the daily changes in our lives. However, it has not been well understood how the memory of past experiences interacts with current input information to update memory.
They found that PPC neuronal populations active during past experiences mediate the interaction between past and present information and update memories via the anterior cingulate cortex (ACC). Furthermore, artificial silencing of this PPC neuronal populations immediately after retrieval of updated memory (fear memory) dissociated the interaction without affecting individual memories stored in the hippocampus and amygdala, indicating that the fear was successfully separated from the fear memory.
This research on the mechanism of memory updating is an achievement that will lead to the elucidation of the higher brain functions of humans, which accurately store each memory and update them as needed. In addition, flashbacks are a major symptom of post-traumatic stress disorder (PTSD) and are triggered by stimuli that existed in the vicinity of the traumatic experience, many of which are related in some way to everyday events. Therefore, the present results are expected to be useful for research aimed at preventing intrusive flashbacks in patients with PTSD.
Original article information
A cortical cell ensemble in the posterior parietal cortex controls past experience-dependent memory updating
Akinobu Suzuki, Sakurako Kosugi, Emi Murayama, Eri Sasakawa, Noriaki Ohkawa, Ayumu Konno, Hirokazu Hirai & Kaoru Inokuchi
As for past experiences, when a mouse is placed in a square box, it remembers the location and stores it in CA1 of the hippocampus (blue line). Then, when they have a new experience (electroshock experience) in the same place (square box), the electroshock experience is stored in the BLA of the amygdala (purple line). At this time, the PPC is activated by the recall of past experiences (green line) and new experiences (purple line), and the fear memory is formed by linking the electroshock experience to the place memory via the ACC (red line).
In this way, PPC neuronal populations recruited during past experiences cooperate with the ACC to update memories by comparing recalled memories with current experiences and linking them as necessary.