Shunting inhibition

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.[1] This form of inhibition is termed "shunting" 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 and, following Ohm's law, the amplitude of subsequent excitatory postsynaptic potential (EPSP) is reduced. This simple scenario arises if the inhibitory synaptic reversal potential is identical to the resting potential.[2]

Shunting inhibition is theorized to be a type of gain control mechanism, regulating the responses of neurons.[3][4] Simple inhibition such as hyperpolarization has a subtractive effect on the depolarization caused by concurrent excitation, whereas shunting inhibition can in some cases account for a divisive effect.[5]

Some evidence exists that shunting inhibition can have a divisive effect on neuronal responses, at least on subthreshold postsynaptic potentials.[6] 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."[5]

Thus, shunting inhibition does not provide a plausible mechanism for neuronal gain modulation.[5]

References
  1. Koch, Christof. "Coding & Vision Lesson 4: Cell Types". Allen Institute.
  2. scholarpedia
  3. Eccles, JC (1964). The Physiology of Synapses. Berlin: Springer-Verlag.
  4. Blomfield S (March 1974). "Arithmetical operations performed by nerve cells". Brain Res. 69 (1): 115–24. doi:10.1016/0006-8993(74)90375-8. PMID 4817903.
  5. Abbott LF, Chance FS (2005). Drivers and modulators from push-pull balanced synaptic input. Progress in Brain Research. 149. pp. 147–155. doi:10.1016/S0079-6123(05)49011-1. ISBN 9780444516794. PMID 16226582. Archived from the original on 2013-02-02.
  6. Holt G.R. & Koch, C. (1997). "Shunting Inhibition Does Not Have a Divisive Effect on Firing Rates". Neural Computation. 9 (5): 1001–1013. CiteSeerX 10.1.1.27.8715. doi:10.1162/neco.1997.9.5.1001. PMID 9188191.


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