  Learning and memory relies on synapses changing their strengths in response
to neural activity. However there is a substantial gap between the timescales
of neural electrical dynamics (1-100 ms) and organism behaviour during learning
(seconds-minutes). What mechanisms bridge this timescale gap? What are the
implications for theories of brain learning? Here I first cover experimental
evidence for slow-timescale factors in plasticity induction. Then I review
possible underlying cellular and synaptic mechanisms, and insights from recent
computational models that incorporate such slow-timescale variables. I conclude
that future progress on understanding brain learning across timescales will
require both experimental and computational modelling studies that map out the
nonlinearities implemented by both fast and slow plasticity mechanisms at
synapses, and crucially, their joint interactions.
