Using　event-related　functional　magnetic　resonance　imaging　(fMRI)　and　the　Ebbinghaus　paradigm,　we　investigated　the　effect　of　memory　in　parietal　cortex　activity.　In　the　course　of　one　week,　participants　learned　Boolean　arithmetic　tasks　and　were　asked　to　master　them　perfectly.　We　measured　cerebral　activation　with　fMRI　while　healthy　volunteers　had　learned　and　practiced　Boolean　rules　on　day　1　(i.e.,　labile　memory　condition)　and　day　7　(i.e.,　stabilized　condition).　A　network　of　cortical　areas　was　found　to　be　differently　activated　during　retrieval　of　labile　and　stabilized　memory,　including　the　left　superior　parietal　lobule　and　precuneus　for　labile　memory　and　the　left　inferior　parietal　lobule　and　postcentral　gyrus　for　labile　and　stabilized　memory.　These　results　show　that　statespecific　cortical　networks　are　systematically　activated　during　memory　retrieval.　We　propose　that　memory　stability　following　the　automatic　retrieval　of　rules　involves　information　clustering　across　time　and,　simultaneously,　to　process　the　repetitive　Boolean　problems　with　minimal　resources　by　mediation　of　parietal　areas.　©　2010　IEEE.