Neurogenesis paradoxically decreases both pattern separation and memory interference

Abstract

The hippocampus has been the focus of memory research for decades. While the functional role of this structure is not fully understood, it is widely recognized as being vital for rapid yet accurate encoding and retrieval of associative memories. Since the discovery of adult hippocampal neurogenesis in the dentate gyrus by Altman and Das in the 1960's, many theories and models have been put forward to explain the functional role it plays in learning and memory. These models postulate different ways in which new neurons are introduced into the dentate gyrus and their functional importance for learning and memory. Few if any previous models have incorporated the unique properties of young adult-born dentate granule cells and the developmental trajectory. In this paper, we propose a novel computational model of the dentate gyrus that incorporates the developmental trajectory of the adult-born dentate granule cells, including changes in synaptic plasticity, connectivity, excitability and lateral inhibition, using a modified version of the Restricted Boltzmann machine. Our results show superior performance on memory reconstruction tasks for both recent and distally learned items, when the unique characteristics of young dentate granule cells are taken into account. Even though the hyperexcitability of the young neurons generates more overlapping neural codes, reducing pattern separation, the unique properties of the young neurons nonetheless contribute to reducing retroactive and proactive interference, at both short and long time scales. The sparse connectivity is particularly important for generating distinct memory traces for highly overlapping patterns that are learned within the same context.

Multi-domain cognitive assessment of male mice reveals whole body exposure to space radiation is not detrimental to high-level cognition and actually improves pattern separation

“…Computational models support that decreased neurogenesis may enhance sparse encoding (140,141) , which as mentioned above may explain why we see improved pattern separation yet other groups see decreased performance in their behavioral tests.…”

Memory Traces Diminished by Exercise Affect New Learning as Proactive Facilitation

“…New adult-born neurons integrating into a synaptic circuit might either replace or coexist with the existing synapse, which can lead to forgetting of consolidated memories (Finnegan and Becker, 2015). In addition, neurons that are newly born at certain stages (about 3-4 weeks in mice) have special characteristics that lead them to be more sensitive than mature neurons during memory encoding.…”

Running rewires the neuronal network of adult-born dentate granule cells

“…On the other hand, in mature GCs in the outer molecular layer (mGC-OGCL), considered to be born during development (Nowakowski and Rakic, 1981), synaptic inhibition was strongly increased, possibly due to interneuron sprouting of axonal collaterals onto these cells (Zhang et al, 2009) in runners. Such a process may underlie the proposed enhancement of sparse encoding by feedback inhibition mediated by hilar cells (McAvoy et al, 2015; Finnegan and Becker, 2015). Our results also provide insight into studies in which all mice were housed with running wheels (Schmidt-Hieber et al, 2004; Marín-Burgin et al, 2012; Temprana et al, 2015).…”