Combine sour cream and baking soda in small bowl; allow to work while mixing rest of loaf. Cream together butter and sugar. Add eggs and vanilla. Combine dry ingredients and mix alternately with sour cream into batter mixture. In a separate bowl, mix cinnamon and brown sugar filling. In a greased loaf pan, alternate a third of the batter mixture with a third of the filling; repeat. Swirl with knife. Bake at 350ºF/ 180ºC for 1 to 1-1/2 hours.