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Transcranial Magnetic and Electric Stimulation
Published in Ben Greenebaum, Frank Barnes, Biological and Medical Aspects of Electromagnetic Fields, 2018
Shoogo Ueno, Masaki Sekino, Tsukasa Shigemitsu
Long-term potentiation (LTP) is a long-lasting increase in the efficacy of synaptic transmission resulting from a high frequency stimulation (Bliss et al., 1973). LTP in the hippocampus is thought to be a typical model of synaptic plasticity related to learning and memory. The most commonly used protocol for LTP induction is an electric stimulation to hippocampus slices. Electric stimulation to the hippocampus slices, typically to the Schaffer collaterals, generates excitatory postsynaptic potentials (EPSPs) in the postsynaptic CA1 cells. If the Schaffer collaterals are stimulated only two or three times per minute, the magnitude of the evoked EPSP in the CA1 neurons remains constant. However, a brief, high-frequency train of stimuli to the same neurons causes LTP, which is evident as a long-lasting increase in EPSP magnitude, as shown in Figure 10.13(a) (Ogiue-Ikeda et al., 2003a,2003b). This high-frequency electric stimulation of a neuron is called tetanus stimulation.
Toxic Effects
Published in Ronald Scott, of Industrial Hygiene, 2018
To understand the components and functioning of this system, visualize the response of a gardener bitten by an insect. The insect bite stimulates sensory cells in the skin. These sensory cells convert the stimulus into a pattern of nerve impulses, moving potential changes at the membrane surface of the connecting nerve cell, which is the manner by which the nervous system transfers information. Such a message moves the length of the nerve cell. At the end of the cell the signal transfers to the next nerve cell in the pathway through a synapse. Synaptic transmission involves the release of a chemical called a neurotransmitter from the end of the first cell, diffusion of that chemical across a very small gap between the cells, and binding of the chemical to a receptor on the second cell. The receptor then initiates a nerve impulse in the second cell. In this fashion the message moves from the sensory cells through the nerves of the peripheral nervous system, to a synaptic connection with the spinal cord. The message now moves up the spinal cord to a location in the brain intended to receive this sort of signal. In the brain the signal is passed around a series of nerve pathways that interpret its meaning and determine the correct action. This involves the use of many synapses, and results in the generation of nerve impulses in appropriate motor (muscle-activating) systems. These impulses travel down the spinal cord, exiting at the correct opening in the vertebral column. The message is delivered to the correct muscles, again through a synapse, and the muscles contract to cause the hand to swat the insect.
Introduction
Published in Andrea Varsavsky, Iven Mareels, Mark Cook, Epileptic Seizures and the EEG, 2016
Andrea Varsavsky, Iven Mareels, Mark Cook
Synaptic transmission is the process by which action potentials arriving at the end of the axon of a transmitting (pre-synaptic) neuron are interpreted by the dendrites of the receiving cell (post-synaptic neuron). The pre-synaptic cell releases chemicals known as neurotransmitters that control the response of the post-synaptic cell. The type of neurotransmitter released varies but these chemicals are responsible for generating a post-synaptic potential (PSP) that can fall in one of two categories: Excitatory post-synaptic potential (EPSP): The response at the synapse is much like a miniature version of an action potential in the post-synaptic cell, except longer in duration and smaller in amplitude. An EPSP is shown relative to the action potential in Figure 1.5. The generation of an EPSP brings the soma closer to threshold and thus increases the likelihood that an action potential is fired.Inhibitory post-synaptic potential (IPSP): Opposite in effect to an EPSP. The probability of a resultant action potential decreases.
Neurophysiological and molecular approaches to understanding the mechanisms of learning and memory
Published in Journal of the Royal Society of New Zealand, 2021
Shruthi Sateesh, Wickliffe C. Abraham
Experimentally, LTP is a process whereby a brief period of high-frequency synaptic activity produces a long-lasting increase in synapse efficacy (Figure 2). The properties of LTP, such as cooperativity, input specificity, and associativity, are fundamental to its putative role in learning and memory in mammals. Cooperativity refers to the fact that LTP induction has a threshold, necessitating the cooperative interaction of multiple afferent fibres working together (McNaughton et al. 1978). LTP is input specific as its induction is restricted to the synapses activated by the high-frequency stimulation rather than all synapses that contact the same neuron (Andersen et al. 1977). The associativity property of LTP is particularly of interest, given its analogy to associative learning. Here, synapses that are unable to produce LTP due to a weak level of input activity can still undergo LTP when they are co-activated alongside strong input stimulation of neighbouring synapses, which will of course also undergo LTP induction (Bliss and Collingridge 1993). Note that in such paradigms, other synapses not activated by either set of stimulated inputs will not be potentiated, due to the input specificity property of LTP. Finally, both LTP and memory can be rapidly induced in regions throughout the brain, are reversible and can exist for shorter or longer periods of time (Eichenbaum et al. 1996; Abraham et al. 2002).
Biological function simulation in neuromorphic devices: from synapse and neuron to behavior
Published in Science and Technology of Advanced Materials, 2023
Hui Chen, Huilin Li, Ting Ma, Shuangshuang Han, Qiuping Zhao
Synapse is the specialized site where one neuron communicates with another, which consists of a presynaptic membrane, synaptic cleft, and postsynaptic membrane. The average neuron forms several thousand synaptic connections and receive a similar number with its neighboring neurons. Synaptic transmission is basic to the brain functions, such as perception, learning and memory. Two modes of synaptic transmission are found in all neurons: electrical and chemical. Based on this, the synapses are divided into electrical and chemical synapses (Figure 1(c)).
Emerging photoelectric devices for neuromorphic vision applications: principles, developments, and outlooks
Published in Science and Technology of Advanced Materials, 2023
Yi Zhang, Zhuohui Huang, Jie Jiang
Between two neurons, the action potential generated by the presynaptic neuron travels through the axon to the terminal presynaptic membrane, which then releases the neurotransmitters. These neurotransmitters have different mechanisms of action. They recognize and bind to receptors on the postsynaptic membrane, causing excitatory or inhibitory changes in the postsynaptic membrane potential. When the potential accumulation in the postsynaptic neuron reaches a threshold, the postsynaptic neuron generates an action potential. This triggers excitatory/inhibitory postsynaptic currents (EPSC and IPSC), which complete the signaling process between the two neurons [76,77]. According to the Hebbian learning rule [78], the strength of synaptic connections (synaptic weights) between two interconnected neurons changes after they experience the synchronized firing activities. This phenomenon, in which the efficiency of synaptic information transmission between neurons increases or decreases with the changes in their neural activities, is called as synaptic plasticity [79]. The realization of functions such as visual information learning and memory is carried out by modulating synaptic plasticity through visual neurons [80]. There are many forms of synaptic plasticity which can be divided into STP and LTP according to the length of memory [81,82]. STP refers to the fact that synaptic weights are maintained for only a few seconds to minutes after stimulation, followed by a gradual return to the initial state. Its synaptic weight changes include short-term potentiation (STP) and short-term depression (STD) [83]. PPF and PPD are two important synaptic functions that reflect STP. The PPF refers to the phenomenon that for two consecutive stimuli, the second stimulus triggers a stronger response than the first [30]. PPD is the opposite of it [82]. LTP means that synaptic weights can be maintained for hours to days or even longer after stimulation, and it is closely related to biological learning and memory functions. It is usually divided into long-term potentiation (LTP) and long-term depression (LTD) [84]. They represent excitatory and inhibitory changes in synaptic weight during repeated stimulation, respectively. STP can also be transformed into LTP under certain conditions. In addition, there are other synaptic plasticity behaviors, such as spiking-rate-dependent plasticity (SRDP), spiking-timing-dependent plasticity (STDP), associative learning, and learning-experience [85]. They are the basis of neural signal processing and neural computation at synapses.