Editing M'Naghten rules (section)

===Disease of the mind===
Whether a particular condition amounts to a disease of the mind within the Rules is not a medical but a legal question to be decided in accordance with the ordinary rules of interpretation. It seems that any disease which produces a malfunctioning of the mind is a disease of the mind and need not be a disease of the brain itself. The term has been held to cover numerous conditions:
{{unordered list
| In ''R v Kemp'' [1957] 1 QB 399 [[arteriosclerosis]] or a hardening of the arteries caused loss of control during which the defendant attacked his wife with a hammer. This was an internal condition and a disease of the mind.
| In ''[[R v Sullivan]]'' [1984] AC 156 during an [[epilepsy|epileptic]] episode, the defendant caused [[grievous bodily harm]]: epilepsy was an internal condition and a disease of the mind, and the fact that the state was transitory was irrelevant.
| In ''R v Quick; R v Paddison'' [1973] QB 910<ref>{{cite web|url = http://www.bailii.org/ew/cases/EWCA/Crim/1973/1.html |website=BAILII|title =  R v Quick & Anor [1973] EWCA Crim 1 (18 April 1973) }}</ref> the defendant committed an assault while in a state of [[hypoglycaemia]] caused by the insulin he had taken, the alcohol he had consumed and not eating properly. It was ruled that the judge should have left the defence of automatism open to him, so his conviction was quashed (he had pleaded guilty rather than not guilty by reason of insanity). This was where the internal/external divide doctrine was first expressed, probably due to judicial reluctance to hospitalise someone for a condition that could be cured by a sugar lump. It is doubtful that a jury would have accepted a defence of automatism, but nonetheless the issue should have been left to them.
| In ''R v Hennessy'' [1989] 1 WLR 287<ref>{{cite web|url = http://www.bailii.org/ew/cases/EWCA/Crim/1989/1.html |website=BAILII|title = Hennessy, R. v [1989] EWCA Crim 1 (27 January 1989) }}</ref> a diabetic stole a car and drove it while suffering from a mild attack of [[hyperglycaemia]] caused by stress and a failure to take his insulin. [[Geoffrey Lane, Baron Lane|Lane LCJ]] said at 294
<blockquote>
In our judgment, stress, anxiety and depression can no doubt be the result of the operation of external factors, but they are not, it seems to us, in themselves separately or together external factors of the kind capable in law of causing or contributing to a state of automatism. They constitute a state of mind which is prone to recur. They lack the feature of novelty or accident, which is the basis of the distinction drawn by [[Kenneth Diplock, Baron Diplock|Lord Diplock]] in ''R v Sullivan'' 1984 AC 156, 172. It is contrary to the observations of Devlin J., to which we have just referred in ''Hill v Baxter'' (1958) 1 QB 277, 285. It does not, in our judgment, come within the scope of the exception of some external physical factor such as a blow on the head or the administration of an anaesthetic.
</blockquote>
| In ''Bratty v Attorney-General for Northern Ireland'' [1963] AC 386<ref>{{cite web|url=http://www.bailii.org/uk/cases/UKHL/1961/3.html|title =  Bratty v Attorney General of Northern Ireland [1961] UKHL 3 (03 October 1961) |website= BAILII}}</ref> [[Lord Denning]] observed ''[[obiter dicta|obiter]]'' that a crime committed while sleepwalking would appear to him to be one committed as an automaton. However, the ruling in ''R v Sullivan'' that diseases of the mind need have no permanence led many academics to suggest that sleepwalkers might well be found to be suffering from a disease of the mind with internal causes unless there was clear evidence of an external causal factor.
| In ''[[R v Burgess]]'' [1991] 2 QB 92 the Court of Appeal ruled that the defendant, who wounded a woman by hitting her with a video recorder while sleepwalking, was insane under the M'Naghten Rules. Lord Lane said, "We accept that sleep is a normal condition, but the evidence in the instant case indicates that sleepwalking, and particularly violence in sleep, is not normal."
}}

The courts have clearly drawn a distinction between internal and external factors affecting a defendant's mental condition. This is partly based on risk of recurrence, whereby the High Court of Australia has expressed that the defence of automatism is unable to be considered when the mental disorder has been proved transient and as such not likely to recur.<ref>R v Falconer (1990) 171 CLR 30 at 30 [http://www.austlii.edu.au/au/cases/cth/HCA/1990/49.html AUSTLII]</ref> However, the distinction between insanity and automatism is difficult because the distinction between internal and external divide is difficult. 

Many diseases consist of a predisposition, considered an internal cause, combined with a precipitant, which would be considered an external cause. Actions committed while sleepwalking would normally be considered as "non-insane automatism", but often alcohol and stress trigger bouts of sleepwalking and make them more likely to be violent. The diabetic who takes insulin but does not eat properly&nbsp;– is that an internal or external cause?