You are presuming reductionism, where higher order things like morality, purpose, and consciousness, can be reduced to lower level things like neurons, or quarks. The most famous explicit reductionist is Patricia Churchland, whose most recent relevant work is Braintrust: https://www.amazon.com/Braintrust-Neuroscience-Tells-about-Morality/dp/0691156344 Churchland has done a lot of writing, and has inspired a lot of other authors, so there will be a large selection to dig into further of related works.
Another noteworthy reductionist is Daniel Dennett, whose latest major work is here: https://www.amazon.com/Bacteria-Bach-Back-Evolution-Minds/dp/0393242072 this book is not explicitly on how to live life, but Dennett is a polymath and will touch on it. Dennett himself is a prolific writer, and if this work does not specifically address your interest, he has multiple other books that may.
However, global reductionism is now a small minority position in philosophy of science, although it remains the majority view among neurologists. Most philosophers follow the sciences and consider sciences either their own independent truth systems (pluralism), OR to be emergent from and only dependent to a limited degree upon their substrates. This includes the vast majority of physicalist philosophers.
For an emergence view, psychology would be EMERGENT FROM, not defined by neurology. And sociology would be EMERGENT FROM, not defined by psychology. And morality would be EMERGENT FROM, not defined by sociology. So, even for a physicalist who accepts emergence, neurology would be nearly useless to try to figure out what we should do with our life, as that is a question so many tiers away, that neurology would give almost no insights.
And for a pure pluralist view, there would be no value whatsoever to what neurology might suggest about values and purposes.
So -- if one accepts non-reductionist thinking, goals and purposes have to be studied and understood as their own separate field/subject.