Adult Neurogenesis in the Hippocampus From a Perspective of Discrimination and Generalization: A Hypothesis

Abstract

The function of adult neurogenesis in the dentate gyrus is not yet completely understood, though many competing theories have attempted to explain the function of these newly-generated neurons. Most theories give adult neurogenesis a role in aiding known hippocampal/dentate gyrus functions. Other theories offer a novel role for these new cells based on their unique physiological qualities, such as their low excitability threshold. Many behavioral tests have been used to test these theories, but results have been inconsistent and often contradictory. Substantial variability in tests and protocols may be at least partially responsible for the mixed results. On the other hand, conflicting results arising from the same tests can serve as aids in elucidating the function of adult neurogenesis. Here, we offer a hypothesis that considers the cognitive nature of tasks commonly used to assess the function of adult neurogenesis, and introduce a dichotomy between tasks focused on discrimination vs. generalization. We view these two aspects as opposite ends of the continuous spectrum onto which traditional tests can be mapped. We propose that high neurogenesis favors behavioral discrimination while low adult neurogenesis favors behavioral generalization of a knowledge or rule. Since many tasks require both, the effects of neurogenesis could be cancelled out in many cases. Although speculative, we hope that our view presents an interesting and testable hypothesis of the effect of adult neurogenesis in traditional behavioral tasks. We conclude that new, carefully designed behavioral tests may be necessary to reach a final consensus on the role of adult neurogenesis in behavior.

Microglia at center stage: a comprehensive review about the versatile and unique residential macrophages of the central nervous system

“…Microglia also contributes substantially to adult neurogenesis [ 10 , 120 – 123 ], which takes place in the dentate gyrus for the hippocampus [ 124 ], the subventricular zone for the olfactory system [ 125 , 126 ] and in the hypothalamus for the neuro-endocrine system [ 127 ]. Life-long adult neurogenesis is required for the function of memory, olfaction, neuroendocrine system and possibly others.…”

“…Life-long adult neurogenesis is required for the function of memory, olfaction, neuroendocrine system and possibly others. As for the development of the CNS, in adult neurogenesis, enhanced or reduced generation of new neurons and their integration may substantially influence the brain function [ 124 ]. Neurogenesis is influenced by microglia [ 128 ] either by producing corresponding supporting or suppressing factors, or by eliminating new neurons [ 129 ], as well as by sustaining new neurons alive.…”

Catalpol enhanced physical exercise-mediated brain functional improvement in post-traumatic stress disorder model via promoting adult hippocampal neurogenesis

“…Adult hippocampal neurogenesis provides the structural plasticity to hippocampal networks to enhance the adaptability of animal to environmental stress [ 3 ]. In the dentate gyrus (DG) region of the hippocampus, neural stem cells (NSCs) experience the systematic biological events from proliferation, neural fate commitment, neural differentiation and maturation that form the newborn neurons to integrate into neural circuits [ 4 ]. The new formed neurons in DG region engage the hippocampus to separate the environmental cues and support the discrimination among the danger and safety surroundings [ 5 ].…”

Study on Effect of Simvastatin on Regeneration of Hippocampal Dentate Gyrus Nerve after Cerebral Ischemia in Rats

“…Simvastatin is a kind of lipid-lowering drug. In recent years, studies have found that simvastatin can also promote nerve regeneration and protect neurological function [3] . Hippocampus is closely related to learning and memory function and is often involved in cerebral ischemia [4] .…”