Whilst our experiences shape the specifics of our brains throughout life, we know that there are a lot of shared properties between us. We all share the same basic layout as, for example, the V1 cortex is always in the same place. Thus it is evident that whilst some of the neural development is experience-dependent, some of it is hereditary/genetic or "hard wired".
It would seem to me that the extent to which the brain is "hard wired" depends on the species. Humans seem to have a lot more room for specialisation in life, whereas some animals don't exhibit much individuality, tending to follow very regular behavioural patterns that have no doubt evolved over time, subject to natural selection.
I have read up to some degree on how experience-dependent development works, but have been largely unable to find any detailed research into how experience-independent development works. That is, how does DNA encode these "hard wired" neural circuits?
Furthermore, the human brain contains some 100 billion neurons. If I assume that maybe 1% of them are "hard wired" into circuits from birth, that's still a billion neurons, each with several connections to other neurons that need to be somehow coded into a DNA sequence which only amounts to a couple of gigabytes worth of data. So how is the complex structure of these "hard wired" (experience-independent) neural circuits encoded in such a limited amount of DNA? How much of the brain is actually hard wired in this way and how much is open to experience-based development? Am I right in associating this process with the phenomenon of "instinct", that is, "hard coded" behavioural patterns in animals which appear to be hereditary?
Is there a name for this field of study? Specifically the study of how neural circuits are generated in the earliest stages, to lay down the high level structure of the brain before experience-based development can take over?