Memristors have relatively simple behavior: they’re a type of circuitry where the present resistance to current is a product of the currents that have flowed through them in the past. The more current that goes through, the easier it will travel through in the future.
Memristors can be made of metal oxides. In this case, the authors used a combination of aluminum oxide and titanium dioxide (Al2O3 and TIO2) to form a memristor. The neural network was formed by linking traditional circuitry through a grid of wiring (technically a crossbar).
The neural network was trained to identify three letters (V, N, and Z), including the possibility of single-pixel errors. After a single time through the training set, the network was able to successfully identify all three letters, although performance continued to improve with further experience.