Abstract
Hippocampal adult neurogenesis has been associated to many cognitive, emotional, and behavioral functions and dysfunctions, and its status as a selected effect or an “appendix of the brain” has been debated. In this review, we propose to understand hippocampal neurogenesis as the process underlying the “Baldwin effect”, a particular situation in evolution where fitness does not rely on the natural selection of genetic traits, but on “ontogenetic adaptation” to a changing environment. This supports the view that a strong distinction between developmental and adult hippocampal neurogenesis is made. We propose that their functions are the constitution and the lifelong adaptation, respectively, of a basic repertoire of cognitive and emotional behaviors. This lifelong adaptation occurs through new forms of binding, i.e., association or dissociation of more basic elements. This distinction further suggests that a difference is made between developmental vulnerability (or resilience), stemming from dysfunctional (or highly functional) developmental hippocampal neurogenesis, and adult vulnerability (or resilience), stemming from dysfunctional (or highly functional) adult hippocampal neurogenesis. According to this hypothesis, developmental and adult vulnerability are distinct risk factors for various mental disorders in adults. This framework suggests new avenues for research on hippocampal neurogenesis and its implication in mental disorders.
Highlights
The existence, nature, and function of adult neurogenesis (AN) in some discrete areas of the central nervous system has been controversial almost since its discovery by Altman and Das [1, 2]
We propose that developmental hippocampal neurogenesis (DHN), i.e., the formation of dentate gyrus (DG) during development, underlies the initial setting up of a repertoire of basic, adaptable behaviors while adult hippocampal neurogenesis (AHN), i.e., the addition of new neurons in the DG during adulthood, underlies adult ontogenetic adaptation
New neurons are continuously added in the DG, and we propose that their function is to modulate and adapt the basic behaviors acquired during development, in the face of life events
Summary
The existence, nature, and function of adult neurogenesis (AN) in some discrete areas of the central nervous system has been controversial almost since its discovery by Altman and Das [1, 2]. We and others have shown that manipulating the activity of a given DGNs population can produce or not behavioral deficits depending on the cell age but not on the number of tagged cells [52, 94] from a functional point of view, evidence points to important differences between developmentally and adult-born neurons.
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