 During the 1950s the number of operations declined by more than half, in spite of the fact that Moniz had received a Nobel Prize for psychosurgery in 1949.Reasons for this decline included increasing concern about the deaths and damage caused by the operation, the introduction of neuroleptic drugs, and changing ideas about the nature and treatment of mental illness.By the mid-1970s the use of psychosurgery had declined still further to about 100–150 operations a year, and nearly all were of the modified type.