It is still difficult for me to think about mind equals brain in terms of physical causes-effects.
In physics a cause, like electricity presence, produces an effect, like a light on or an engine movement.
Whereas, the absence of electricity produces another effect, like a light off or an engine not moving.
In the brain, an effect like a psysical movement of an arm is produced by an electro-chemical stimulus (the mind thought "I move my arm"). But an effect like an arm not moving is still produced by an electro-chemical stimulus (the mind thought "I do not move my arm" or "I (just) think of moving my arm without doing it").
In the latest case, think about the thought "imagine a pink elephant" which should correspond to the electro-chemical state X (visualisation of a pink elephant) and then think about the thought "do not imagine a pink elephant" which should still correspond to the electro-chemical state X (visualisation of a pink elephant), because it is impossible not to think about a pink elephant without thinking it...