**7. Review criteria**

The PubMed database (NCBI, National Library of Medicine, USA) was searched for relevant, both original and review, articles using the keywords mentioned at the beginning of the present chapter either by separate or with multiple combinations. The papers were selected accordingly to their adhesion to the main subject of the present review and the expert authors' knowledge of the field. In addition, interesting and useful information has been achieved from http://www.alzforum.org/ and http://clinicaltrials.gov/, as well as from books at the Library of the University of the Balearic Islands (Palma de Mallorca, Spain).
