Bartol Jr, T. M., Bromer, C., Kinney, J., Chirillo, M. A., Bourne, J. N., Harris, K. M.,
& Sejnowski, T. J. (2015). Nanoconnectomic upper bound on the variability of synaptic plasticity.
Elife, 4, e10778. https://cdn.elifesciences.org/articles/10778/elife-10778-v2.pdf
Electron microscopy reconstruction
Hippocampus
Previous studies (including glutamate uncaging experiments) have shown that there
is a correlation between the functional strength of a spiny synapse and its size. Bartol et al.
provide additional evidence by showing how tight size correlates between synapses with
identical histories of pre- and post-synaptic firing. They interpret residual variability to estimate
an upper bound on the precision of synaptic strengths.
“The strong correlation between size and efficacy of a synapse allowed us to estimate
the variability of synaptic plasticity. In an EM reconstruction of hippocampal neuropil we found
single axons making two or more synaptic contacts onto the same dendrites, having shared
histories of presynaptic and postsynaptic activity. The spine heads…of these pairs were nearly
identical in size. We found that there is a minimum of 26 distinguishable synaptic strengths,
corresponding to storing 4.7 bits of information at each synapse.”