A few questions because my prof is a dead beat.

Hi, I'm still in my early years of psychology and my school kinda sucks. I have this appetite for psych but having trouble sating it. So I decided to ask the coolest subreddit. Here it goes.

On Classical Conditioning:

Are there upper and lower time limits to when a neutral stimulus can become a conditioned stimulus?

Is there a difference between being conditioned for positive responses and being conditioned for negative responses?

On memory:

Where is memory stored physically? What is the physical basis of how information becomes matter?

I understand that retrieving memory involves the synapses. But where is it retrieved from? Not just from long-term memory, I mean physically. Is it that different memories fire up different and unique neural paths? and then when we retrieve that memory do those paths get used once again?

Help me Psychit, you're my only hope.