Overview: Guest host: Mo Rocca. In our cover story, Susan Spencer meets a pioneer in the study of stroke recovery. Plus: David Pogue explains the GameStop stock battle pitting Wall Street hedge funds against day traders; Rocca talks with Mark Harris, author of a new biography of director Mike Nichols; Holly Williams profiles actor and Negroni-mixer Stanley Tucci; Tracy Smith talks with Andra Day and Lee Daniels, star and director of a new film about legendary jazz singer Billie Holiday; and Martha Teichner tells the story behind her new book, "When Harry Met Minnie," a true tale of puppy love and friendship.