Simulated Apoptosis/Neurogenesis Regulates Learning and Memory Capabilities of Adaptive Neural Networks

Abstract

Characterization of neuronal death and neurogenesis in the adult brain of birds, humans, and other mammals raises the possibility that neuronal turnover represents a special form of neuroplasticity associated with stress responses, cognition, and the pathophysiology and treatment of psychiatric disorders. Multilayer neural network models capable of learning alphabetic character representations via incremental synaptic connection strength changes were used to assess additional learning and memory effects incurred by simulation of coordinated apoptotic and neurogenic events in the middle layer. Using a consistent incremental learning capability across all neurons and experimental conditions, increasing the number of middle layer neurons undergoing turnover increased network learning capacity for new information, and increased forgetting of old information. Simulations also showed that specific patterns of neural turnover based on individual neuronal connection characteristics, or the temporal-spatial pattern of neurons chosen for turnover during new learning impacts new learning performance. These simulations predict that apoptotic and neurogenic events could act together to produce specific learning and memory effects beyond those provided by ongoing mechanisms of connection plasticity in neuronal populations. Regulation of rates as well as patterns of neuronal turnover may serve an important function in tuning the informatic properties of plastic networks according to novel informational demands. Analogous regulation in the hippocampus may provide for adaptive cognitive and emotional responses to novel and stressful contexts, or operate suboptimally as a basis for psychiatric disorders. The implications of these elementary simulations for future biological and neural modeling research on apoptosis and neurogenesis are discussed.

Erythropoietin Enhances Hippocampal Response during Memory Retrieval in Humans

“…Newborn cells take weeks to mature but may influence learning processes in early stages because of unique properties such as increased capacity for long-term potentiation, a main neurobiological mechanism underlying early memory formation (Aimone et al, 2006). Computational simulation shows that neurogenesis improves network capacity for new information storage and forgetting of old irrelevant information (Chambers et al, 2004). Increased hippocampal neurogenesis may hence improve learning and adaptive cognitive and emotional responses to novel challenging contexts, whereas reduced neurogenesis might impair ability to cope with stress and be a basis for psychiatric disorders like depression (Chambers et al, 2004).…”

“…Computational simulation shows that neurogenesis improves network capacity for new information storage and forgetting of old irrelevant information (Chambers et al, 2004). Increased hippocampal neurogenesis may hence improve learning and adaptive cognitive and emotional responses to novel challenging contexts, whereas reduced neurogenesis might impair ability to cope with stress and be a basis for psychiatric disorders like depression (Chambers et al, 2004). If upregulation of BDNF-mediated neuroplasticity and neurogenesis in the hippocampus and increased response in hippocampus-dependent tasks are important factors in the treatment of depression as hypothesized, Epo seems a promising candidate for novel treatment strategies.…”

“…Adult neurogenesis is believed to play a key role in learning and memory and adaptation to novel circumstances (Chambers et al, 2004). Stress-induced elevation of glucocorticoids has been reported to decrease hippocampal neurogenesis and cause spatial learning deficits (Kitraki et al, 2004) and depression-like behavior in rodents (Malberg and Duman, 2003).…”

Is there a link between adult neurogenesis and learning?

“…Although new neurons are predicted by some computational theories of learning (Chambers et al, 2004;Diesseroth et al, 2004;Becker, 2005), their precise role is not yet known. It has been suggested that the production of new cells in the DG increases the opportunity for learning in the future by providing more cells that can be recruited into existing circuits (Kempermann, 2002).…”

The Role of Hippocampal Atrophy in Depression: A Neurocomputational Approach

“…In a study using a three-layer feedforward perceptron model, Chambers et al [26] simulated the effect of neuronal turnover (neuron loss and reposition in the hidden layer maintaining a constant number of neurons) to explore the cognitive significance of a possible functional association of apoptotic and neurogenic events in the dentate gyrus of the hippocampus. Their results show that elimination and replacement of neurons enhances the speed of learning new information but reduces accuracy in the recall of old information.…”