Shunting inhibition, also known as divisive inhibition, is a form of
postsynaptic potential inhibition that can be represented mathematically as reducing the
excitatory potential by division, rather than linear subtraction. The term "shunting" is used because of the
synaptic conductance short-circuit
A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. ...
currents that are generated at adjacent
excitatory synapse
An excitatory synapse is a synapse in which an action potential in a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell. Neurons form networks through which nerve impulses travel, each neuron ofte ...
s. If a shunting inhibitory synapse is activated, the
input resistance The input impedance of an electrical network is the measure of the opposition to current ( impedance), both static ( resistance) and dynamic ( reactance), into the load network that is ''external'' to the electrical source. The input admittance (the ...
is reduced locally. The amplitude of subsequent
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 ...
(EPSP) is reduced by this, in accordance with
Ohm's Law.
This simple scenario arises if the inhibitory synaptic reversal potential is identical to the resting potential.
Discovery
Shunting inhibition was discovered by Fatt and Katz in 1953.
Mechanism
Shunting inhibition is theorized to be a type of
gain control mechanism, regulating the responses of
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s.
Simple inhibition such as
hyperpolarization has a subtractive effect on the
depolarization
In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is ess ...
caused by concurrent excitation, whereas shunting inhibition can in some cases account for a divisive effect.
Some evidence exists that shunting inhibition can have a divisive effect on neuronal responses, at least on
subthreshold postsynaptic potentials.
In a 2005 article, researchers Abbott and Chance state that "Although the importance of gain modulation and multiplicative interaction in general has been appreciated for many years, it has proven difficult to uncover a realistic biophysical mechanism by which it can occur. It is important to note that, despite comments in the literature to the contrary (see above), divisive inhibition of neuronal responses cannot arise from shunting inhibition. This has been shown theoretically as well as experimentally – inhibition has the same subtractive effect on firing rates whether it is of the shunting or hyperpolarizing variety."
Thus, shunting inhibition does not provide a plausible mechanism for
neuronal gain modulation.
See also
Synaptic depression
Synaptic may refer to:
* Synapse, part of the nervous system
* Synaptic (software), a Linux graphical package management program
* Synaptics
Synaptics is a publicly owned San Jose, California-based developer of human interface (HMI) hardware ...
References
Neurophysiology
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