I have seen several lines that point to dynamic modifications of the learning rate.
The amygdala certainly releases learning promoters when a particularly significant event happens.
The link to the RAS/RAC works to gate “more” of anomalous input which indirectly serves to increase vigilance and learning. More on this: I think that the cortex is always weakly “resonating” with the senses and if the cortex can find a loose match nothing special happens. If there is some degree of surprise the RAS detects the mis-match between the input stream and the cortex as “surprise” that needs attention. The RAC opens up the firehose of sensation flooding the cotex with a strong stream of sensation which is learned with our online/one-shot learning until enlightenment is achieved. (The cortex, resplendent in its newfound learning, resonates with the input stream!) This is how I have come to view the “spotlight of attention” that was proposed by Francis Crick.
http://www.pnas.org/content/pnas/81/14/4586.full.pdf
There are some other mechanisms but these are the ones that I feel the most certain of.