Use it or lose it: How neurogenesis keeps the brain fit for learning

Abstract

The presence of new neurons in the adult hippocampus indicates that this structure incorporates new neurons into its circuitry and uses them for some function related to learning and/or related thought processes. Their generation depends on a variety of factors ranging from age to aerobic exercise to sexual behavior to alcohol consumption. However, most of the cells will die unless the animal engages in some kind of effortful learning experience when the cells are about one week of age. If learning does occur, the new cells become incorporated into brain circuits used for learning. In turn, some processes of learning and mental activity appear to depend on their presence. In this review, we discuss the now rather extensive literature showing that new neurons are kept alive by effortful learning, a process that involves concentration in the present moment of experience over some extended period of time. As these thought processes occur, endogenous patterns of rhythmic electrophysiological activity engage the new cells with cell networks that already exist in the hippocampus and at efferent locations. Concurrent and synchronous activity provides a mechanism whereby the new neurons become integrated with the other neurons. This integration allows the present experience to become integrated with memories from the recent past in order to learn and predict when events will occur in the near future. In this way, neurogenesis and learning interact to maintain a fit brain.

Long-Lasting Plasticity of Hippocampal Adult-Born Neurons

“…In particular, hippocampal-dependent learning promotes the survival of newborn cells generated 1 week before training, as a function of task difficulty. Trace eye blink conditioning and spatial learning (reference memory or delayed matching to place) exert a survival-promoting effect (Shors et al, 2012), whereas active shock avoidance and fear contextual memory are insufficient to change cell survival (Pham et al, 2005;Van der Borght et al, 2005;LopezFernandez et al, 2007). More recently, we have discovered that learning-induced survival of these immature neurons depends upon the elimination of youngest newborn cells at a specific developmental period (Drapeau et al, 2007;Dupret et al, 2007;Tronel et al, 2010).…”

Adult Hippocampal Neurogenesis in Natural Populations of Mammals

“…"Use It or Lose It" in Free-Living Mammals Shors et al (2012) have formulated the "use-itor-lose-it" concept for AHN in laboratory rodents, as many behavioral experiments that include some forms of learning increase the survival rates of young cells. Free-living mammals have to cope with a multitude and, in many ways, continually changing stimuli throughout their life.…”

Seasonal Variation in Cell Proliferation and Cell Migration in the Brain of Adult Red-Sided Garter Snakes <b><i>(Thamnophis sirtalis parietalis)</i></b>

“…For example, the survival of new brain cells is enhanced by spatial navigation learning during Morris water maze tests in rats and mice [reviewed in Shors, 2008;Shors et al, 2012]. Similarly, Hoshooley and Sherry [2007] showed that greater neuron recruitment in the hippocampus is associated with food caching in adult black-capped chickadees, i.e.…”