CREATE TABLE table_name_91 (channels___analog___digital__ VARCHAR(255), first_air_date VARCHAR(255), region_served VARCHAR(255))
What channels first aired on 31 December 1990 in the Southern Downs region?
    
SQL: SELECT channels___analog___digital__ FROM table_name_91 WHERE first_air_date = "31 december 1990" AND region_served = "southern downs"