Microtubules have a variety of important functions in cellular structure, usually of a motile nature. They form cilia, flagella and the asters which pull apart chromosomes in mitosis and meiosis. The cilia found in the lining of bronchial tubes, vital for the cleanliness of the lungs, and the cilia which give mobility to a paramecium both consist of microtubules.
Microtubules are also found scattered throughout the cytoplasm of dendrites. The microtubules have an important property- that their resistance to the passage of an electric current is significantly less than that of the surrounding cytoplasm. In this sense they are like elements of wiring.
Now here is the idea- When an action potential travels along a certain path through the dendrites of the brain, if the microtubules would migrate to align themselves with this path there would be a greater likelyhood that next time the action potential would travel this particular path. Further repetitions would cause further alignment.
The resulting path would offer lower resistance for the passage of further action potentials and this path would be favoured.
Thus a "memory route" is strengthened. Any further refreshment of the bit of knowledge involved would strengthen recall- as is found by experience. Recall itself would increase the facility of future recall.