Sept 29 (Reuters) - Facebook Inc (FB.O) plans to highlight internal research that shows teenage girls felt better after using its Instagram app during a Senate hearing to be held on Thursday, according to the company"s prepared testimony seen by Reuters. The social media giant has been under fire for the past week after the Wall Street Journal reported internal documents showed Facebook was aware that Instagram harmed the mental health of young users. Antigone Davis, global head of safety at Facebook, will detail the company"s previously announced efforts to better protect kids and teens online, including defaulting users under the age of 16 to private accounts when they join Instagram, according to the testimony. U.S. Senator Richard Blumenthal announced the hearing titled "Protecting Kids Online” following the Journal"s reporting.Internal Facebook research shows that among teenage girls who said they had recently felt sadness, 57% said Instagram made things better, Davis" prepared remarks show. Among teenage girls who felt loneliness, 51% said Instagram had a positive impact, according to the testimony. On Tuesday, a Facebook whistleblower will testify about the company and how it handles children"s safety online at a Senate hearing featuring Blumenthal and Senator Marsha Blackburn. The senators did not give any information about the whistleblower. read more