Elicited Fear Response in Mice Depends on the Size of Their Environment
Kaitlyn E. Dorst, Ryan A. Senne, Anh H. Diep, Antje R. de Boer, Rebecca L. Suthard et al.
(see article e0340232023)
Learning when and how to respond to threats is critical for survival. Memories of external threats are “stored” in groupings of cells in the hippocampus. These groups of cells, also called engrams, reliably fire together as exposure to their respective stimuli occurs. Experimenters can artificially manipulate engrams within the hippocampus to control the retrieval of fear memories, which has enabled much discovery. However, how engrams are activated to drive specific fear responses in different contexts remains unknown. An action such as freezing can be attributed to the reactivation of a fear engram, but the relationship between the cells in this engram and different environments that engage them was unexplored prior to a study in this issue. Dorst and colleagues stimulated a hippocampal fear engram in male mice in three differently sized arenas. Mice froze in response to engram activation in the smallest space, but not in the largest. The authors then performed graph theoretical analyses to discover that engram reactivation in the different arenas corresponded to different brain-wide network dynamics. The findings of this study reveal that defensive fear responses and their corresponding brain dynamic changes are context dependent, which suggests that fear memory-encoding cell ensembles can be flexibly engaged. While it is imperative that sex differences are further explored, these findings may inform the development of new treatment strategies for disorders in which aberrant fear responses alter the quality of life.
Representative 20× image of the activity-dependent tagging of a hippocampal engram from a mouse conditioned in the large chamber experimental condition. In blue (DAPI) are cell bodies. The ensemble is tagged with GFP (green) and endogenous cFos (red) is expressed when cells are activated. Arrows depict overlap of the two. Scale bar: 50 µM.
Novel Insights on the Neural Representation of Movement
Seda Karakose-Akbiyik, Oliver Sussman, Moritz F. Wurm, and Alfonso Caramazza
(see article e1363232023)
Detecting and understanding movement is crucial for our interactions with the world. Previous work on the neural basis of movement perception has primarily focused on understanding human action. However, the forces that drive and control movement do not have to be tied to humans or be agentive. For instance, a rock being thrown by a human involves agentive control because its movement is tied to an animate being. However, a rock rolling down a hill can be explained fully by physical forces without animate intervention. In this paper, Karakose-Akbiyik and colleagues explored whether there are differences in the way the brain represents agentive versus physical event dynamics. They imaged human brains with fMRI and found that activity patterns in frontoparietal and posterior temporal cortices captured information about agentive and physical movement in an aligned way. However, they also found differences in the neural representation of agentive and physical events, whereby the right lateral occipitotemporal cortex was more sensitive to agentive event dynamics and the left dorsal premotor cortex was more sensitive to inanimate object movement driven by physical force. These findings provide novel insights into the brain regions that support action recognition. Furthermore, they highlight the need for addressing both agentive and physical aspects of movement in future studies investigating motion and perception.
Footnotes
This Week in The Journal was written by Paige McKeon
