The Scottish actress, who plays housekeeper Mrs. Hughes in the hit period drama, launched Dementia UK's Time For A Cuppa campaign on Wednesday (21Nov12) to raise money to fund teams of specialist mental health nurses.
The cause is close to Logan's heart as she spent 10 years nursing her mother-in-law through the illness, which affects brain function and causes symptoms including memory loss and disorientation.
She says, ""I really feel there has to be joined-up thinking on the part of the Government, hospitals and other organisations so that sufferers and their carers are offered the very best care and support.""
The campaign, which encourages supporters to throw fundraising tea parties, will run from 1-8 March 2013. Last year (12) it raised $87,561 (£54,820) for the charity.