Lukin's comments today came after the president of Russia's Independent Psychiatric Association, Yuri Savenko, examined Arap and said she was institutionalized without any medical basis.
Arap, who is active with the opposition United Civic Front, claims authorities in the Murmansk region placed her in the hospital in July in reprisal for a statement she gave to a newspaper, alleging that patients at a psychiatric clinic were beaten and sexually abused.
Arap's daughter, Taisiya Arap, has launched a legal appeal against her mother's detention.
Human-rights groups have warned that the case may represent a return to Soviet-era tactics of using psychiatric diagnoses and detentions to suppress opposition.
RFE/RL Russia Report
SUBSCRIBE For news and analysis on Russia by e-mail, subscribe to "RFE/RL Russia Report."