From the SfN website:
G20 Summit in Downtown Washington
As Neuroscience 2008 approaches, SfN is monitoring Washington heightened security in effect due to the G20 summit meeting at the National Building Museum. No disruption of meeting activities is anticipated, but some street closures are probable, as are minor disruptions on the Washington Metropolitan Area Transit system (Metro). The Judiciary Square station's F street entrance will close at 7 p.m. on Friday, November 14. Station access will be available through the 4th and D street entrance. On Saturday, the entire Judiciary Square station will be closed until 8 p.m. Trains will travel through the station, but will not stop. Most hotels are near other Metro stops that will be in operation. Check Metro's Web site for updates and enjoy the meeting.