Shunting Inhibition
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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 currents that are generated at adjacent excitatory synapses. If a shunting inhibitory synapse is activated, the input resistance 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 Ohm's law states that the electric current through a Electrical conductor, conductor between two Node (circuits), points is directly Proportionality (mathematics), proportional to the voltage across the two points. Introducing the constant of ...
. This simple scenario arises if the inhibitory synaptic reversal potential is identical to or even more negative than the
resting potential The relatively static membrane potential of quiescent cells is called the resting membrane potential (or resting voltage), as opposed to the specific dynamic electrochemical phenomena called action potential and graded membrane potential. The re ...
.


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 (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...
s. Simple inhibition such as hyperpolarization has a subtractive effect on the
depolarization In biology, depolarization or hypopolarization is a change within a cell (biology), cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolar ...
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


References

Neurophysiology {{neuroscience-stub