Is evidence of a criminal defendant's mental retardation admissible in the second degree murder trial?

Evidence of a criminal defendant's mental retardation "is not admissible 'to show or negate the capacity to form any mental state,' but is admissible solely on the issue whether the accused ' actually formed a required specific intent . . . when a specific intent crime is charged.' " (People v. Smithey (1999) 20 Cal.4th 936, 958 (Smithey); 28, subd. (a); see also People v. Cortes (2011) 192 Cal.App.4th 873, 902.) "In the guilt phase of a criminal action, any expert testifying about a defendant's mental [retardation] shall not testify as to whether defendant had or did not have the required mental states, which include, but are not limited to, purpose, intent, knowledge, or malice aforethought, for the crimes charged. The question as to whether the defendant had or did not have the required mental states shall be decided by the trier of fact." ( 29; Smithey, supra, at p. 958.)

The mental state required for second degree murder is malice aforethought, and malice aforethought can be either express or implied. A defendant acts with express malice aforethought if he unlawfully intends to kill. A defendant acts with implied malice if he intentionally commits an act; the natural consequences of the act are dangerous to human life; at the time he acts, he knows his act is dangerous to human life; and he deliberately acts with conscious disregard for human life. (See CALCRIM No. 520.) "To support a defense of 'diminished actuality,' a defendant presents evidence of voluntary intoxication or mental condition to show he 'actually' lacked the mental states required for the crime. [Citation.]" (People v. Clark (2011) 52 Cal.4th 856, 880, fn. 3.) "[T]he jury may generally consider evidence of voluntary intoxication or mental

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