Do all neurons have something to do (i.e. all are activated for some known stimuli), and when a novel stimuli appear some of them change in some way so we can learn it? Or is it that we have "new"/"unused" neurons (i.e. do not fire for any known stimuli), and when a novel stimuli appear, they can continue the chain of neurons and "learn" it (i.e. activated when it appears)?
If it's the former, how do only some of the neurons change (in comparison to all) to be activated for the novel stimuli, and what is that change?
If it's the latter, do the unused neurons compete for the novel stimuli? How do the unused neurons "know" to "pick up" the novel stimuli? i.e. be activated for it
I understand that if neuron A is activated very often with neuron B, at some point it's very likely that they will have a connection (Hebbian theory). But how would novel knowledge be incorporated? i.e. a new neuron that we never had before, or an existing one that somehow decides to change, be suddenly activated for the novel input, and form a synapse with an existing neuron?