Associations and synaptic reinforcement

[thenewdeal]

So my quandary is when the brain thinks of a thought say a bear it forms a nuerochemical pattern or pathway associated with that thought. By thinking about "bear" the brain reinforces that pattern in the brain ie "use it or lose it". And when the brain is busy thinking about something else that pathway weakens. 

So say you have two unrelated thoughts positive and negative, bacon and the death of a loved one for example, by just having those two thoughts simultaneously present in your brain a connection or association be it weak could form between the two. There is no logical reason they should be associated except for the fact they popped in the brain at about the same time. 
There is now a neural link between two unrelated thoughts and the more one thinks about it the stronger that superficial link becomes, creating a snowball effect. Is there a way to sever this link? 

I know the more I think about something the less my brain wants to keep thinking about it and wants to think about anything else, but I don't know what this mechanism is called. I also know synaptic pruning plays a role in trimming thoughts and connections that are underused. 

I've made a disturbing association between two things I don't want connected and not wanting them to connect seems only to connect them more, as I am painfully aware that on a brain biochemical level I'm only reinforcing this association whenever I think about it. I don't know how to break this self reinforcing chain in my mind. I used to think that thinking was a neutral act, I didn't understand that I reinforce whatever I'm thinking about. Now that I'm aware that I cannot think about things without charging or strengthening them in my mind neurologically I'm afraid that whatever I think about particularly negative things have the chance to get stuck in my brain. Like a hamster wheel that only gets progressively faster the more you think about it.

I suspect that the answer might lie in caloric conservation and management, thinking about a thought, firing that pattern of synapses repeatedly depletes its chemical resources so the brain almost automatically switches its firing and thinks about something else while said synapses replenish themselves. Again I am uneducated in this field of brain science so any information as to how these things work would be illuminating. 

Any help with this would be greatly appreciated.