In Parks, LaForest classified automatism as a sub-set of voluntariness, part of the actus reus component of criminal liability.
We can add that voluntariness, and not consciousness, is the key element of automatistic behaviour since the defence of amounts to a of the actus reus.
The that people . The legal burden then in cases involving claims of automatism must be on the defence to prove involuntariness on the balance of probabilities to the trier of fact. This burden is justified under s. 1 of the Charter.
The defence must call expert psychiatric or psychological evidence confirming the assertion but they’re not done yet. The trial judge can examine all other evidence from the severity of the triggering stimulus to whether there is a motive for the crime.
The legal test for what legally constitutes a disease of the mind involves an assessment of the particular evidence in the case rather than a general principle of law and is thus a question of mixed law and fact.
Trial judges should start from the proposition that the condition the accused claims to have suffered is a disease of the mind. Then they must determine whether the evidence takes the condition out of that category (Rabey approach).
S.M. Beck and G.E. Parker, The Intoxicated Offender—A Problem of Responsibility (1966), 44 Can. Bar Rec. 563 at 570-573.
We don’t know precisely what happens when someone becomes intoxicated.
Medical science has a broad idea of what happens and this might well justify a change in degree of responsibility attributed to the intoxicated offender.
Intoxication impairs perception, judgment and muscular coordination while increasing self-confidence, lessening inhibitions, and releasing aggressive impulses.
Intoxicated people might be quite incapable of foreseeing the consequences of their acts.
Voluntariness is the issue: acutely intoxicated person may have no more appreciation of acts and their consequences than psychotic person.
But society deems the act of becoming intoxicated as irresponsible in itself, so there is a compromise between the criminal law requirement of a voluntary act and the social judgment that a wrongdoer not be exonerated simply because he was drunk.
R. v. Bernard  2 S.C.R. 833