Long-term depression (LTD) is an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer following a long patterned stimulus.Īll neurofeedback uses EEG, which is a test used to evaluate the electrical activity in the brain. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons. Long-term potentiation is a persistent strengthening of synapses based on recent patterns of activity. The axon hillock is the primary site where postsynaptic potentials (EPSPs and IPSPs) are summed to determine whether to initiate an action potential. The phenomenon of long-term potentiation, where synaptic efficiency increases due to activation, has been proposed as an explanation for why neurofeedback training effects persist. Inhibitory Post Synaptic Potential: These are the opposite of EPSP, and are a decrease in outgoing positive charges, that makes a postsynaptic neuron l ess likely to generate an action potential. This temporary depolarisation 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. a pair of equal and oppositely charged or magnetised poles separated by a distance) that can be identified by the electrodes placed over the scalp.Įxcitatory Post Synaptic Potential: An excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the post synaptic neuron more likely to fire an action potential. There the vesicle fuses with the presynaptic membrane and expels its contents.ĮEG reflects voltages generated (mostly) by excitatory postsynaptic potentials from apical dendrites of massively synchronised neocortical pyramidal cells. Calcium entry into the terminal button causes vesicle movement toward the release zone. This mechanism prevents an action potential from travelling back the way it just came. When an action potential depolarises an axon’s terminal button, this opens voltage-gated calcium ion channels. After an action potential has occurred, there is a transient negative shift, called hyperpolarization or the refractory period, due to additional potassium currents. This allows a neuron to initiate future action potentials. The sodium-potassium transporters exchange 2 potassium ions for every 3 sodium ions expelled from a neuron. A sodium-potassium transporter returns a neuron to its resting voltage following an action potential. As the sodium channels close, sodium ions can no longer enter the neuron, and then they are actively transported back out of the plasma membrane. Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state. The process proceeds until all of the available ion channels are open, resulting in a reversal in the membrane potential from -70mV to +30mV. When the channels open (in response to depolarisation), they allow an inward flow of sodium ions, which changes the electrochemical gradient, which in turn produces a further rise in the membrane potential. (Note Auditory Evoked Potentials can actually be synchronised in a large number of neurons and can be an exception.) Postsynaptic potentials are changes in the membrane potential of the postsynaptic terminal of a chemical synapse. Postsynaptic potentials are graded potentials, and should not be confused with action potentials although their function is to initiate or inhibit action potentials.Īction potentials are generated by special types of voltage-gated ion channels embedded in a cell’s membrane. These channels are shut when the membrane potential is near the resting potential of the cell, but they rapidly begin to open if the membrane potential increases to a precisely defined threshold value (-55mV). Action potentials in the axons do not contribute to the ongoing EEG activity as they are too short, go in too many directions relative to the surface of the cortex and are not synchronised. The electrical activity is measured in pyramidal cells of the cortex, and is related to post-synaptic potentials (PSPs). Electrodes are able to measure electrical activity in superficial parts of the cortex, with a depth around 5mm, and a surface diameter of around 1-2cm.
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