Trends in Neurosciences
Volume 24, Issue 7, 1 July 2001, Pages 381-385
Journal home page for Trends in Neurosciences

Opinion
Short-term synaptic plasticity as a temporal filter

https://doi.org/10.1016/S0166-2236(00)01835-XGet rights and content

Abstract

Synaptic efficacy can increase (synaptic facilitation) or decrease (synaptic depression) markedly within milliseconds after the onset of specific temporal patterns of activity. Recent evidence suggests that short-term synaptic depression contributes to low-pass temporal filtering, and can account for a well-known paradox – many low-pass neurons respond vigorously to transients and the onsets of high temporal-frequency stimuli. The use of depression for low-pass filtering, however, is itself a paradox; depression induced by ongoing high-temporal frequency stimuli could preclude desired responses to low-temporal frequency information. This problem can be circumvented, however, by activation of short-term synaptic facilitation that maintains responses to low-temporal frequency information. Such short-term plasticity might also contribute to spatio–temporal processing.

Section snippets

Synaptic depression and temporal processing

Many sensory neurons in the cortices of mammalian species, sensory systems of invertebrate species, and electrosensory midbrains of some species of fish, respond strongly to low-temporal frequency stimuli, for example <10 Hz (see Fig. 1a,b), and weakly or not at all to ongoing high-temporal frequencies 6, 10, 17, 18, 19. Many of these neurons, paradoxically, respond strongly to sensory transients and the onsets of high-temporal frequency stimuli, even though most of the power in these stimuli

The interplay between synaptic depression and synaptic facilitation

The use of synaptic depression for low-pass temporal filtering presents a paradox. If all the inputs to a neuron experience short-term depression, it might not respond to low-temporal frequency information in the presence of depressing high-temporal frequency stimulation. For many behaviors this would defeat the function of the low-pass filter. For example, as stated above, ongoing high-temporal frequency electrosensory information does not impair behavioral responses to biologically relevant

Conclusions

Independently evolved sensory systems, including the visual system of mammals and electrosensory systems of weakly electric fish, have convergently employed synaptic depression as a mechanism for low-pass temporal filtering. Because other mechanisms exist for achieving this filtering, it is probable that synaptic depression serves some common functional demands in these systems beyond low-pass filtering. Future studies should examine the hypothesis that the depression-induced phase advances in

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