Nature advance online publication 14 January 2009 | doi:10.1038/nature07604;
Received 18 July 2008; Accepted 30 October 2008; Published online 14 January
2009
Synaptic depression enables neuronal gain control
Jason S. Rothman 1, Laurence Cathala 1,2, Volker Steuber 1,2 & R. Angus
Silver 1
1.. Department of Neuroscience, Physiology and Pharmacology, University
College London, Gower Street, London WC1E 6BT, UK
2.. These authors contributed equally to this work.
Correspondence to: R. Angus Silver 1 Correspondence and requests for
materials should be addressed to R.A.S. (Email: [email protected]).
To act as computational devices, neurons must perform mathematical
operations as they transform synaptic and modulatory input into output
firing rate. Experiments and theory indicate that neuronal firing typically
represents the sum of synaptic inputs, an additive operation, but
multiplication of inputs is essential for many computations. Multiplication
by a constant produces a change in the slope, or gain, of the input-output
relationship, amplifying or scaling down the sensitivity of the neuron to
changes in its input. Such gain modulation occurs in vivo, during contrast
invariance of orientation tuning, attentional scaling, translation-invariant
object recognition, auditory processing and coordinate transformations.
Moreover, theoretical studies highlight the necessity of gain modulation in
several of these tasks. Although potential cellular mechanisms for gain
modulation have been identified, they often rely on membrane noise and
require restrictive conditions to work. Because nonlinear components are
used to scale signals in electronics, we examined whether synaptic
nonlinearities are involved in neuronal gain modulation. We used synaptic
stimulation and the dynamic-clamp technique to investigate gain modulation
in granule cells in acute slices of rat cerebellum. Here we show that when
excitation is mediated by synapses with short-term depression (STD),
neuronal gain is controlled by an inhibitory conductance in a
noise-independent manner, allowing driving and modulatory inputs to be
multiplied together. The nonlinearity introduced by STD transforms
inhibition-mediated additive shifts in the input-output relationship into
multiplicative gain changes. When granule cells were driven with bursts of
high-frequency mossy fibre input, as observed in vivo, larger
inhibition-mediated gain changes were observed, as expected with greater
STD. Simulations of synaptic integration in more complex neocortical neurons
suggest that STD-based gain modulation can also operate in neurons with
large dendritic trees. Our results establish that neurons receiving
depressing excitatory inputs can act as powerful multiplicative devices even
when integration of postsynaptic conductances is linear.'
Source: Nature
http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature07604.html?lang=en
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