What is it,that is aware that I Am? 
the individual existence that resides in you ,the enjoyer rather than the enjoyed even though at some points they are the same . 
“What is it that makes the center of our consciousness, where do our activities start” - if we have understood your question correctly.
The center of consciousness of each person is called the Developmental Consciousness of the Soul, and in the physical body it is located in the area of the thymus gland. It is the permanent consciousness of every person, a consciousness that develops and incarnates anew, thus advancing in its development.
“And the brain”?
The brain is the seat of a person’s daily consciousness, because there are four senses in the area of the head. Therefore, the purpose of the operative consciousness that resides in the brain is to process the information collected by the physical senses, to analyze and select them according to their content and importance, and to make conclusions and decisions based on them.
At the end of the day, the mechanisms for going to sleep are activated, then the consciousness from the brain returns to the Developmental Consciousness of the Soul and leaves the physical body, staying on the Life (Etheric), Emotional (Astral) and Thought Plans.
To conclude: the source of consciousness of every person is the Developmental Consciousness of the Soul.
http://images.vfl.ru/ii/1564474408/36fe49bf/27378797.jpg
Awareness, aware of itself becomes I. I, aware of awareness dissolve into That. Love, it flows, as the fragrance of a rose, out into existence such as attention out of I. What it is? That is aware of I am, but a mirror? The stream of life, reflects the I, but the stream itself is a reflection of That. Of what? Of the whiteness behind this words, without which no stream of words would flow. Without stream, no I would form as a reflection either… And all flows, for that movement is life, and life does not sit, so why should I?