Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Redistribution of synaptic efficacy has been observed following Hebbian pairing (Markram and Tsodyks, 1996) and this change reflects a change in U (Tsodyks and Markram, 1997).
Category: