The same happens to my 7 year old here. He usually gets better with magnesium supplement prescribed by a nutritionist, but this time it is not working 100%, although it is helping to diminish the number of outbursts he was having.
While searching on information about his aggressive behavior, I found an interesting link about allergies and behavior as well. It is interesting because he is allergic to a few tree polens and it seems that his aggression periods coincide with spring time. It could also be food allergy/intolerance.