I can't imagine why someone from Caithness living in West Lothian would have been in the asylum in Montrose, but it's not impossible.
Did he die after census day in 1871 (2 April)? If so, might the 1871 census contain some useful snippet?
I did some work on Sutherlands from Caithness who moved to West Lothian for a cousin (on her mother's side) who was a descendant (on her father's side) of Donald Tulloch Sutherland, born 21 November 1835 at Clysterfield, Thurso and died 9 January 1898 in Bathgate. His brother Robert (born 1842 in Thurso) also moved from there to Bathgate but I have nothing on Robert after the 1861 census. Their tree includes 53 Sutherlands born in Latheron, but not, so far, your Robert.
I wonder what impelled Sutherlands from Caithness to move to Bathgate?