Some studies show that visual cortex is activated by mental imagery, too ( See, eg: http://www.nature.com/nature/journal/v378/n6556/abs/378496a0.html http://www

Some studies show that visual cortex is activated by mental imagery, too ( See, eg: http://www.nature.com/nature/journal/v378/n6556/abs/378496a0.html http://www.nature.com/nature/journal/v378/n6556/abs/378496a0... ) so it stands to reason that decoding mental images could be possible.