system
Given the following post, respond as if you're commenting on Reddit:
human
What 'connections' is the brain actually building when you learn something?

Everything I've learned about neuroscience so far has made this statement not really make sense.  What about the synapse is actually changing?
gpt
Here are some properties which can change at the synapse:

1) The sensitivity of the post-synaptic membrane, making it require more or less input to respond with an action potential at the axon.

2) The amount and type of receptors present in the post-synaptic membrane.

4) Production of neurotransmitters in the pre-synaptic terminal.

3) The branching of axons in the pre-synaptic membrane e.g. after nerve damage you can get axonal sprouting of one axon into a now vacant section of dendrites.

The precise physical basis of memory is still largely unknown.