Shunting inhibition

Inhibitory postsynaptic potential

An inhibitory postsynaptic potential is a synaptic potential that decreases the chance that a future action potential will occur in a postsynaptic neuron or α-motoneuron...

is termed "shunting" because the synaptic

Synapse

In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...

 conductance

Conductance

Conductance may refer to:* Electrical conductance, the ability for electricity to flow a certain path* Fluid conductance, the ability for fluid to transmit through materials* Thermal conductivity, the ability for temperatures to transmit through materials...

 short-circuits

Short circuit

A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....

 currents that are generated at adjacent excitatory synapse

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 often making numerous connections with other cells...

s. If a shunting inhibitory synapse is activated, the input resistance is reduced locally and, following Ohm's law

Ohm's law

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points...

, the amplitude of subsequent Excitatory postsynaptic potential

Excitatory postsynaptic potential

In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...

 (EPSPs) is reduced. This simple scenario arises if the synaptic reversal potential is identical to the resting potential.

Shunting inhibition was theorized to be a type of gain control

Control theory

Control theory is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems. The desired output of a system is called the reference...

 mechanism, regulating the responses of neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s.. Simple inhibition such as hyperpolarization has a subtractive effect on the depolarization caused by concurrent excitation, whereas shunting inhibition was hoped to account for a divisive effect.

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.