Adult Neurogenesis in the hippocampus, Potential Roles in Learning and Memory

Jetten, Elles (2018) Adult Neurogenesis in the hippocampus, Potential Roles in Learning and Memory. Bachelor's Thesis, Biology.

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Abstract

For a long time, we have thought that neurons in the adult brain do not proliferate, since a few decades ago this was proven to be false. The presence of newly generating neurons has been shown a lot of different species of mammals, humans included. It is exclusively present in the olfactory bulb and the dentate gyrus of the hippocampus. The function of adult neurogenesis has yet to be elucidated, and in this thesis, we will discuss several theories and evidence about the function of adult neurogenesis in the hippocampus. To infer any potential function for neurogenesis it is important to consider Dentate gyrus anatomy and role in memory. The dentate gyrus receives input from the entorhinal cortex through the perforant pathway and projects to the CA3 region of the hippocampus through mossy fibers. It consists of three distinct cell layers. Hippocampus function is to play a role in memory encoding and recalling. The dentate gyrus is thought to be involved in the sparse and orthogonal presentation of processed sensory information encoding, and the separation of similar patterns. Indeed, it was found in behavioral studies that lesions of this region, or a knock-out of an essential receptor affected pattern separation abilities. Neurogenesis is highly specific for this region, so it would make sense to hypothesize that neurogenesis is necessary to the function of the specific region. Impairment of neurogenesis in multiple ways has been shown to decrease efficacy in spatial separation tasks. On the other hand, augmenting neurogenesis by genetic modification enhances the ability of mice to perform contextual fear discrimination tasks. Development and maturation of new neurons and factors that influence it could be important clues to unraveling the function and characteristics of neurogenesis. Proliferation of neural stem cells are controlled by GABA signaling, and later maturation, and migration of young neurons are enhanced by surrounding GABA, providing a potential negative feedback loop. Young granule cells die in large numbers around 2-3 weeks of age, and survival is activity dependent through NMDA receptor activation. After functional integration young neurons exhibit a sensitive period. Evidence leads to potential functioning of neurogenesis in pattern separation. Also, temporal pattern separation and forgetting are hypothesized functions of neurogenesis. And finally, it is thought that neurogenesis plays a role in emotional memories and HPA-axis modulation. Most of hypotheses mentioned are supported by behavior evidence, neuron characteristics and computational modeling. However, the subject matter makes it inherently difficult to prove direct causal relationships. Future studies and methods may however provide with stronger evidence.

Item Type:	Thesis (Bachelor's Thesis)
Supervisor name:	Havekes, R.
Degree programme:	Biology
Thesis type:	Bachelor's Thesis
Language:	English
Date Deposited:	27 Jul 2018
Last Modified:	30 Jul 2018 14:35
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/18103

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