Explanation of synaptic time constants


Thank you for making this resource available. I have been using it as a reference in my modeling work (mostly single compartmental at present, but it’s still been very useful).

I had a quick question about the synaptic time constants that are reported in the NMC portal. They seem to be much longer than I would expect. For example, I would expect a typical GABA A synapse to have a rise time of ~0.5 ms and a decay time of ~8 ms (references below). (Time constants on this scale are important for the production of PING gamma.) However, many of the time constants from basket cells are reported to be much longer. For example, the L23_LBC to L23_PC rise and decay times are 5.5 and 48 msec, respectively. NBC and SBC have similar time constants.

Is this due to the synaptic response being a mix of GABA A and GABA B ? Is there any way to separate out the individual contributions?

Thank you,
David Stanley
Postdoctoral Researcher, Boston University

Wang, X. J., & Buzsáki, G. (1996). Gamma oscillation by synaptic inhibition in a hippocampal interneuronal network model. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 16(20), 6402–6413. https://doi.org/citeulike-article-id:134404
(GABA A decay of ~10 ms)

Kramer, M. a., Roopun, A. K., Carracedo, L. M., Traub, R. D., Whittington, M. a., & Kopell, N. J. (2008). Rhythm generation through period concatenation in rat somatosensory cortex. PLoS Computational Biology, 4(9). https://doi.org/10.1371/journal.pcbi.1000169
(GABA A decay of ~5 ms for basket cells)


Hi David,

Thanks for your message.

Just to clarify, the time constants shown in the pathway fact-sheets of the NMC portal are rise and decay times of post-synaptic potentials (PSPs) measured in the somata of modeled neurons by in silico current clamp recordings.

Indeed, the rise and decay time constants of GABAA conductances we use to parametrize synaptic transmission in the digital reconstruction of neocortical microcircuitry is consistent with the values you pointed out.

Also, for the L23_LBC to L23_PC connection, rise and decay times are 5.5 and 48 msec, because the composite PSP contains both GABAA and GABAB components. Yes, the individual components could be separated.

What values are you looking for? time constants for synaptic conductances or potentials?