Engram formation

January 31, 2017

Santoro A, Frankland PW, Richards BA, “Memory Transformation Enhances Reinforcement Learning in Dynamic Environments”, Journal of Neuroscience, 36 (48), 12228-12242

Over the course of systems consolidation, there is a switch from a reliance on detailed episodic memories to generalized schematic memories. This switch is sometimes referred to as “memory transformation.” Here we demonstrate a previously unappreciated benefit of memory transformation, namely, its ability to enhance reinforcement learning in a dynamic environment. We developed a neural network that is trained to find rewards in a foraging task where reward locations are continuously changing. The network can use memories for specific locations (episodic memories) and statistical patterns of locations (schematic memories) to guide its search. We find that switching from an episodic […]
June 24, 2015

Yiu AP, Mercaldo V, Yan C, Richards BA, Rashid AJ, Hsiang HL, Pressey J, Mahadevan V, Tran MM, Kushner SA, Woodin MA, Frankland PW and Josselyn SA, “Neurons are recruited to a memory trace based on relative neuronal excitability at the time of training”, Neuron, 83(3), 722-735

Memories are thought to be sparsely encoded in neuronal networks, but little is known about why a given neuron is recruited or allocated to a particular memory trace. Previous research shows that in the lateral amygdala (LA), neurons with increased CREB are selectively recruited to a fear memory trace. CREB is a ubiquitous transcription factor implicated in many cellular processes. Which process mediates neuronal memory allocation? One hypothesis is that CREB increases neuronal excitability to bias neuronal recruitment, although this has not been shown experimentally. Here we use several methods to increase neuronal excitability and show this both biases recruitment into […]
June 24, 2015

Richards BA and Frankland PW, “The conjunctive trace”, Hippocampus, 23(3), 207-212

Memories serve to establish some permanence to our inner lives despite the fleeting nature of subjective experience. Most neurobiological theories of memory assume that this mental permanence reflects an underlying cellular permanence. Namely, it is assumed that the cellular changes which first occur to store a memory are perpetuated for as long as the memory is stored. But is that really the case? In an opinion piece in this issue of Hippocampus, Aryeh Routtenberg raises the provocative idea that the subjective sense of memory persistence is not in fact a result of persistence at the cellular level, rather, that “supple […]
June 24, 2015

Sekeres MJ, Mercaldo V, Richards BA, Sargin D, Mahadevan V, Woodin MA, Frankland PW and Josselyn SA, “Increasing CRTC1 function in the dentate gyrus during memory formation or reactivation increases memory strength without compromising memory quality”, The Journal of Neuroscience, 32(49), 17857-17868

Memory stabilization following encoding (synaptic consolidation) or memory reactivation (reconsolidation) requires gene expression and protein synthesis (Dudai and Eisenberg, 2004; Tronson and Taylor, 2007; Nader and Einarsson, 2010; Alberini, 2011). Although consolidation and reconsolidation may be mediated by distinct molecular mechanisms (Lee et al., 2004), disrupting the function of the transcription factor CREB impairs both processes (Kida et al., 2002; Mamiya et al., 2009). Phosphorylation of CREB at Ser133 recruits CREB binding protein (CBP)/p300 coactivators to activate transcription (Chrivia et al., 1993; Parker et al., 1996). In addition to this well known mechanism, CREB regulated transcription coactivators (CRTCs), previously called […]