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Long-term Depression
In neurophysiology, long-term depression (LTD) is an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer following a long patterned stimulus. LTD occurs in many areas of the CNS with varying mechanisms depending upon brain region and developmental progress. As the opposing process to long-term potentiation (LTP), LTD is one of several processes that serves to selectively weaken specific synapses in order to make constructive use of synaptic strengthening caused by LTP. This is necessary because, if allowed to continue increasing in strength, synapses would ultimately reach a ceiling level of efficiency, which would inhibit the encoding of new information. Both LTD and LTP are forms of synaptic plasticity. Characterisation LTD in the hippocampus and cerebellum have been the best characterized, but there are other brain areas in which mechanisms of LTD are understood. LTD has also been found to occur in different types of neurons that rele ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chronic Depression
Dysthymia ( ), also known as persistent depressive disorder (PDD), is a mental and behavioral disorder, specifically a disorder primarily of mood, consisting of similar cognitive and physical problems as major depressive disorder, but with longer-lasting symptoms. The concept was used by Robert Spitzer as a replacement for the term "depressive personality" in the late 1970s. In the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), dysthymia is a serious state of chronic depression, which persists for at least two years (one year for children and adolescents). Dysthymia is not a minor form of major depressive disorder, and for some may be more disabling. As dysthymia is a chronic disorder, those with the condition may experience symptoms for many years before it is diagnosed, if diagnosis occurs at all. As a result, they may believe that depression is a part of their character, so they may not even discuss their symptoms with doctors, family members or friends. I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metabotropic Glutamate Receptor
The metabotropic glutamate receptors, or mGluRs, are a type of glutamate receptor that are active through an indirect metabotropic process. They are members of the group C family of G-protein-coupled receptors, or GPCRs. Like all glutamate receptors, mGluRs bind with glutamate, an amino acid that functions as an excitatory neurotransmitter. Function and structure The mGluRs perform a variety of functions in the central and peripheral nervous systems: For example, they are involved in learning, memory, anxiety, and the perception of pain. They are found in pre- and postsynaptic neurons in synapses of the hippocampus, cerebellum, and the cerebral cortex, as well as other parts of the brain and in peripheral tissues. Like other metabotropic receptors, mGluRs have seven transmembrane domains that span the cell membrane. Unlike ionotropic receptors, metabotropic glutamate receptors are not ion channels. Instead, they activate biochemical cascades, leading to the modification ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ligand-gated Ion Channel
Ligand-gated ion channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand), such as a neurotransmitter. When a presynaptic neuron is excited, it releases a neurotransmitter from vesicles into the synaptic cleft. The neurotransmitter then binds to receptors located on the postsynaptic neuron. If these receptors are ligand-gated ion channels, a resulting conformational change opens the ion channels, which leads to a flow of ions across the cell membrane. This, in turn, results in either a depolarization, for an excitatory receptor response, or a hyperpolarization, for an inhibitory response. These receptor proteins are typically composed of at least two different domains: a transmembrane domain which includes the ion pore, and an extracellular domain ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Excitatory Postsynaptic Potential
In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential, caused by the flow of positively charged ions into the postsynaptic cell, is a result of opening ligand-gated ion channels. These are the opposite of inhibitory postsynaptic potentials (IPSPs), which usually result from the flow of ''negative'' ions into the cell or positive ions ''out'' of the cell. EPSPs can also result from a decrease in outgoing positive charges, while IPSPs are sometimes caused by an increase in positive charge outflow. The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC). EPSPs, like IPSPs, are graded (i.e. they have an additive effect). When multiple EPSPs occur on a single patch of postsynaptic membrane, their combined effect is the sum of the individual EPSPs. Larger EPSPs result in greater membr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schaffer Collateral
Schaffer collaterals are axon collaterals given off by CA3 pyramidal cells in the hippocampus. These collaterals project to area CA1 of the hippocampus and are an integral part of memory formation and the emotional network of the Papez circuit, and of the hippocampus, hippocampal trisynaptic loop. It is one of the most studied synapses in the world and named after the Hungarian anatomist-neurologist Károly Schaffer. As a part of the hippocampal structures, Schaffer collaterals develop the limbic system, which plays a critical role in the aspects of learning and memory. The signals of information from the contralateral CA3 region leave via the Schaffer collateral pathways for the CA1 pyramidal neurons. Mature synapses contain fewer Schaffer collateral branches than those synapses that are not fully developed. Many scientists try to use the Schaffer collateral synapse as a sample synapse, a typical excitatory glutamatergic synapse in the Cerebral cortex, cortex that has very well been ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, and plays important roles in the consolidation of information from short-term memory to long-term memory, and in spatial memory that enables navigation. The hippocampus is located in the allocortex, with neural projections into the neocortex in humans, as well as primates. The hippocampus, as the medial pallium, is a structure found in all vertebrates. In humans, it contains two main interlocking parts: the hippocampus proper (also called ''Ammon's horn''), and the dentate gyrus. In Alzheimer's disease (and other forms of dementia), the hippocampus is one of the first regions of the brain to suffer damage; short-term memory loss and disorientation are included among the early symptoms. Damage to the hippocampus can also re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Action Potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and in some plant cells. Certain endocrine cells such as pancreatic beta cells, and certain cells of the anterior pituitary gland are also excitable cells. In neurons, action potentials play a central role in cell-cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon; these signals can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of event ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterosynaptic Plasticity
Synaptic plasticity refers to a chemical synapse's ability to undergo changes in strength.Purves, D., Augustine, G.J., Fitzpatrick, D., Hall, W.C., LaMantia, A.S., White, L.E. (2012). Synaptic Plasticity. In Neuroscience (5th ed.) (pp. 163-182). Sunderland, Massachusetts: Sinauer Associates. Synaptic plasticity is typically input-specific (i. e. homosynaptic plasticity), meaning that the activity in a particular neuron alters the efficacy of a synaptic connection between that neuron and its target. However, in the case of heterosynaptic plasticity, the activity of a particular neuron leads to input unspecific changes in the strength of synaptic connections from other unactivated neurons.Lynch, G.S., Dunwiddie, T., and Gribkoff, V. (1977). Heterosynaptic depression: a postsynaptic correlate of long-term potentiation. Nature 266, 737–739.Abraham, W.C., and Goddard, G.V. (1983). Asymmetric relationships between homosynaptic long-term potentiation and heterosynaptic long-term depressi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homosynaptic Plasticity
Homosynaptic plasticity is one type of synaptic plasticity.Purves, D., Augustine, G. J., Fitzpatrick, D., Hall, W. C., LaMantia, A. S., White, L. E. (2012). Synaptic Plasticity. In Neuroscience (5th ed.) (pp. 163-182). Sunderland, Massachusetts: Sinauer Associates. Homosynaptic plasticity is input-specific, meaning changes in synapse strength occur only at post-synaptic targets specifically stimulated by a pre-synaptic target.Byrne, J. (1997)Synaptic Plasticity.In Neuroscience Online (Section 1, Chapter 7). Therefore, the spread of the signal from the pre-synaptic cell is localized. Another type of synaptic plasticity, heterosynaptic plasticity, is not input-specific and differs from homosynaptic plasticity in many mechanisms. In addition to being input-specific, the strengthening of a synapse via homosynaptic plasticity is associative, because it is dependent on the firing of a presynaptic and postsynaptic neuron closely in time. This associativity increases the chances that the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BCM Theory
BCM theory, BCM synaptic modification, or the BCM rule, named for Elie Bienenstock, Leon Cooper, and Paul Munro, is a physical theory of learning in the visual cortex developed in 1981. The BCM model proposes a sliding threshold for long-term potentiation (LTP) or long-term depression (LTD) induction, and states that synaptic plasticity is stabilized by a dynamic adaptation of the time-averaged postsynaptic activity. According to the BCM model, when a pre-synaptic neuron fires, the post-synaptic neurons will tend to undergo LTP if it is in a high-activity state (e.g., is firing at high frequency, and/or has high internal calcium concentrations), or LTD if it is in a lower-activity state (e.g., firing in low frequency, low internal calcium concentrations). This theory is often used to explain how cortical neurons can undergo both LTP or LTD depending on different conditioning stimulus protocols applied to pre-synaptic neurons (usually high-frequency stimulation, or HFS, for LTP, or l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metaplasticity
Metaplasticity is a term originally coined by W.C. Abraham and M.F. Bear to refer to the plasticity of synaptic plasticity. Until that time synaptic plasticity had referred to the plastic nature of ''individual'' synapses. However this new form referred to the plasticity of the plasticity itself, thus the term ''meta''-plasticity. The idea is that the synapse's previous history of activity determines its current plasticity. This may play a role in some of the underlying mechanisms thought to be important in memory and learning such as long-term potentiation (LTP), long-term depression (LTD) and so forth. These mechanisms depend on current synaptic "state", as set by ongoing extrinsic influences such as the level of synaptic inhibition, the activity of modulatory afferents such as catecholamines, and the pool of hormones affecting the synapses under study. Recently, it has become clear that the prior history of synaptic activity is an additional variable that influences the synaptic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Negative Feedback
Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances. Whereas positive feedback tends to lead to instability via exponential growth, oscillation or chaotic behavior, negative feedback generally promotes stability. Negative feedback tends to promote a settling to equilibrium, and reduces the effects of perturbations. Negative feedback loops in which just the right amount of correction is applied with optimum timing can be very stable, accurate, and responsive. Negative feedback is widely used in mechanical and electronic engineering, and also within living organisms, and can be seen in many other fields from chemistry and economics to physical systems such as the climate. General negative feedback systems are studied in control systems engineering. Negative feedback ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
