Can a jury consider whether the head injury sustained in hitting the ground affected his ability to form the mental state required to commit murder and attempted murder?

Appellant asserts for the first time on appeal that the head trauma he suffered in hitting the ground affected his ability to form the mental state required to commit murder and attempted murder. He contends the trial court thus erred by not sua sponte instructing the jury that jurors could consider the effect of his injury on his state of mind during the shootings. (Pen. Code, 28, subd. (a); People v. Alvarez (1970) 4 Cal.App.3d 913, 918 [" `It has long been settled that evidence of diminished mental capacity . . . caused by . . . trauma . . . can be used to show that a defendant did not have a specific mental state essential to an offense' "].) He alternatively argues that if the court did not have a sua sponte duty to give such an instruction, his defense lawyer provided ineffective assistance of counsel by not requesting the instruction.