Inflammatory modulation of learning and memory- A role for hippocampal neurogenesis?
Hippocampal neurogenesis
Neurogenesis is the birth of new neurons. It is a multistep process which consists of asymmetric division of neural stems ultimately leading to the generation of new neurons. In the hippocampus, neurogenesis occurs predominantly during embryonic development and also during adulthood (Altman and Das, 1965). In the human brain, adult neurogenesis occurs in the subgranular zone of the dentate gyrus throughout life (Eriksson et al., 1998). Newly formed cells in the subgranular layer then migrate to the granular layer of the dentate gyrus where they express a neuronal phenotype (Kuhn et al., 1996). These adult-formed granule cells are integrated into the existing hippocampal circuitry where they participate in hippocampal function after several weeks (Jessberger and Kempermann, 2003).
The role of hippocampal neurogenesis in learning and memory
The extent in which hippocampal neurogenesis plays a role in learning and memory is an active area of research. Evidence suggests that learning enhances adult hippocampal neurogenesis. The effects of associative learning on hippocampal neurogenesis in adult rats were determined by labelling new cells with the thymidine analogue bromodeoxyuridine (BrdU) and analysing these cells after specific behavioural tasks. The number of BrdU labelled cells dramatically increased in the dentate gyrus following specific hippocampus-dependent tasks whereas there was no significant increase after completing hippocampus-independent tasks (Gould et al., 1999).
The object location test (OLT) is a behavioural test to assess the ability of a rodent to differentiate between a familiar and novel spatial locat...
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...lock many affects of IL-1 beta in the central nervous system (Cragnolini et al., 2004).
TNF alpha is thought to be involved in the cognitive effects associated with AIDS Dementia Complex. Young adult rats were chronically infused with TNF alpha before their spatial memory was tested in the morris water maze. After four consecutive daily training sessions during which the platform in the pool was visible, the rats’ spatial memory was tested in a 60 second probe trial with no platform. The data recorded showed that the rats that received the TNF alpha spent considerably less time in the former platform quadrant in comparison to the rats who didn’t receive the TNF alpha infusion (Bjugstad et al., 1998). Because TNF alpha is known to supress neurogenesis, suppression of neurogenesis could be responsible for the spatial memory impairments associated with inflammation.
Hippocampus is a small, curved region, which exists in both hemispheres of the brain and plays a vital role in emotions, learning and acquisition of new information. It also contributes majorly to long term memory, which is permanent information stored in the brain. Although long term memory is the last information that can be forgotten, its impairment has become very common nowadays. The dysfunction is exemplified by many neurological disorders such as amnesia. There are two types of amnesia, anterograde and retrograde. Anterograde amnesia is inability in forming new information, while retrograde refers to the loss of the past memory. As suggested by Cipolotti and Bird (2006), hippocampus’s lesions are responsible for both types of amnesia. According to multiple trace theory, the author suggests that hippocampal region plays a major role in effective retrieving of episodic memory (Cipolotti and Bird, 2006). For example, patients with hippocampal damage show extensively ungraded retrograde amnesia (Cipolotti and Bird, 2006). They have a difficult time in retrieving information from their non-personal episodic events and autobiographical memory. However, this theory conflicts with standard model of consolidation. The difference between these theories suggests that researchers need to do more work to solve this controversy. Besides retrieving information, hippocampus is also important in obtaining new semantic information, as well as familiarity and recollection (Cipolotti and Bird, 2006). For instance, hippocampal amnesic patient V.C shows in ability to acquire new semantic knowledge such as vocabularies and factual concepts (Cipolotti and Bird, 2006). He is also unable to recognize and recall even...
Around the world, many people are living with neurologically debilitating disorders like multiple sclerosis. Multiple sclerosis is best described as a pathological “inflammatory-mediated demyelinating disease of the human central nervous system,” and affects more than 2.5 million people globally (Trapp & Nave, 2008).
The hippocampus has been associated with memory formation and consolidation, through lesions studies of bilateral medial temporal lobectomy patients, such as the famously amnesic H.M. In 1971 with the discovery of place cells by O’Keefe and Dostrovsky, spatial navigation was recognised as one of the primary roles of the hippocampus, with their 1978 book ‘The Hippocampus as a Cognitive Map' O’Keefe and Nadel’s hypothesis has since commanded great influence in the field.
Emerging evidence implicates microglial play critical roles to the CNS development of the brain. Microglial are unique population arise from immature yolk-sac macrophages that migrate and colonize the developing brain (Ginhoux et al., 2010; Ransohoff and Cardona, 2010). Interestingly, microglial (or their precursor cells) are selectively integrating into proliferative neurogenic zone of the proliferation and regulating the size of neural precursor cell pool via phagocytose neural precursor cell upon completion of neurogenesis(Cunningham et al., 2013). Also, colonization of microglia in the developing brain almost concurs temporally with brain vascularisation, neuroepithelial-radial glia transformation, neuronal migration, and myelination. Recent advent of transgenic technology and pharmacology allowed the role of microglia during development and their correlation with neural development disorder to be investigated extensively. For instance, pharmacologically knockout or inactivation of embryonic microglia resulted in increases of neural precursor cells pool (Cunningham et al., 2013). Similar phenomenons were also observed in genetically knockout of microglial in mice. Colony stimulating factor 1R-deficient (Csf1r−/−) mice w...
More in depth, learning plays a role in brain cells growth. Dendrites sprout from the cell body of a neuron which increases in size and number in response to learned skills (Willis, 2008). Also, Willis (2008) mentions that learning ...
Korzus E, Rosenfeld MG, Mayford M. CBP histone acetyltransferase activity is a critical component of memory consolidation. Neuron 2004;42:961-72
The question concerning the plasticity of the mature human brain is one of the unsolved neuroscience issues. Neuroplasticity relates to the different levels of learning ability, ranging from cellular adjustments to large-scale adjustments in cortical remapping. Neuroplasticity is important in the overall healthy development, learning, and memorizing, as well as in the recovery from various types of brain damage. During the 20th century, most neuroscientists agreed that the brain structures were active only during early childhood (Rentería, 2012). However, this assumption has been questioned by various findings that suggest that the brain remains plastic even in adulthood. The growth of the human
A neuron is a cell that transmits information throughout the human brain and nervous system. The average human has approximately 100 billion neurons and about 90% of the neurons are located in the cerebral cortex. For as many neurons there are in the human brain, there are as many neuroglia which serve to protect and support the neurons. Neurons are unlike any other brain cell because at birth the neurons are able to divide and make new cells. The cells divide and increase in size until about the age of eighteen but they last a lifetime. The most interesting part of neurons dividing occurs in the hippocampus. The hippocampus is an area in the human brain essential to memory and is the only area in the brain where neurons continue to divide and increase in size throughout life. (Mastin,
The first neural induction in amphibian embryos has given the Nobel Prize in Medicine award to Hans Spemann in 1935 for his “Spemann-Mangold organizer” paper. The discovery with her student Hilde Mangold leads to establishment of a neuroectodermal primordium from where the nervous system arise involving induction of chemicals such as the fibroblast growth factor (FGF) and WNT signalling, together with inhibition of bone morphogenetic protein-4 (BMP) signalling activity to promotes neuron development. Spemann’s study has successfully identified a morphologically distinct cluster of mesodermal cell located in dorsal lip of blastophore known as ‘organizer’ which has the potential in neural induction. BMP will trigger neural induction and are formed during the gastrulation in vertebrate embryo which is secreted by ventral gastrula signalling centre (Spermann H, Mangold H, 1924). In a normal mechanism BMP binds with receptor on ectoderm cell to form epidermis. However, by inhibiting BMP, ectoderm cells will differentiate to form the neurons cells without the presence of neural inducers t...
The brain contains millions of tiny nerve cells, known as neurons and these neurons are joined and connected to a million more neurons. When these neurons form a series of interconnected neuron...
During early childhood, there is a huge proliferation of connections between neurons, usually peaking around the age of two. The adolescent brain then cuts down the amount of connections, deciding which ones are important to keep and which can be let go. While there are various theories as to the molecular mechanisms by which pruning actually occurs, most agree that pruning is primarily carried out by a very motile form of glial cell, called microglia [1], and pre-programmed cell death (apoptosis). These microglia are thought to remove cellular debris and perform surveillance during the healing process of an injured brain, but in the healthy, developing brain they have a possibly more important function. If a synapse receives little activity, it is weakened and eventually deleted by microglia and other glial cells through a process called long-term depotentiation (LTD). After the synapse has been removed, the space and resources that it once used are taken by other synapses. These synapses are strengthened by long-term potentiation (LTP). These processes and various others take place throughout development, peaking at adolescence and reaching their base around the age of 21, and transform the brain to create more complex and efficient neuronal configurations.
Human brain consists of billions of cells interconnected together, with each performing its separate functions. It consists of two explicit categories of nerves: neurons and glia cells. Neuron is a single nerve cell in the entire nervous system; which is electrically excitable cell that carries information after being processed via chemical or electrical signals. One of its key characteristics is that it does not undergo cell division. In addition, it maintains a voltage gradient for all the neurons across its membranes. Glia cells, on the other hand, its functionality is to maintain homeostasis.
As the human body goes through different experiences, the brain grows, develops, and changes according to the environmental situations it has been exposed to. Some of these factors include drugs, stress, hormones, diets, and sensory stimuli. [1] Neuroplasticity can be defined as the ability of the nervous system to respond to natural and abnormal stimuli experienced by the human body. The nervous system then reorganizes the brain’s structure and changes some of its function to theoretically repair itself by forming new neurons. [2] Neuroplasticity can occur during and in response to many different situations that occur throughout life. Some examples of these situations are learning, diseases, and going through therapy after an injury.
Soloman, G. Psychoneuroimmunology: Interactions between the central nervous system and the immune system. J Neurosci Res 18:1-9 (1987).
Learning to tie shoes and ride a bike requires the encoding, storing, and retrieving of past observations of the procedure. With a lot of practice, children master these skills so well that they are able to remember them the rest of their lives. Memory is the storing of information over time. It is one of the most important concepts in learning; if things are not remembered, no learning can take place. As a process, memory refers to the "dynamic mechanism associated with the retention and retrieval of information about past experiences" (Sternberg 260). We use our memory about the past to help us understand the present. The study or memory in psychology is used in different ways, as well as there are many different ways to study how memory works in humans. In psychology there are many tasks used to measure memory, and different types of memory storages that human's use, such as sensory storing, or short term storing. There are also a lot of techniques that humans use to improve their memory, which they can use to learn, such as mnemonic devices. All these things can be classified as important issues in the study of human memory and ways of learning.