Brain data pertaining to control of emotions through conscious effort is explained by using a quantum mechanical model of the body/brain of the subject. Unlike the classical model, in which all the causal structure is expressed exclusively in terms of the physical variables, the quantum mechanical model involves causal connections between aspects of the subject described in physical termss with aspects described in psychological terms, and it can explain how the latter affects the former. The data is expressed partially in psychological terms of emotions and conscious effort and partially in terms of observations by the scientists of devices that measure physically described properties of the brain. The quantum model allows these differently described aspects to be causally connected, whereas the classical model must reduce everything to the physical description, in order to display the causal links. But the failure of classical mechanics is the failure of the idea that, in situations such as this, where the behaviour of the physical system (the brain) depends sensitively upon the motions of its atomic and ionic constuents, the purely physical descriptions are causally complete.