Just wondered how did Adam get Peter to remember the 4 months that he had forgot, i thought that when the Haitian has cleared memories then that's them gone forever?

He stated it in the episode, that Peter's brain could heal itself, and thereby recover his memories. That indicates that the Haitian's power is not to remove memory, but merely to damage the areas of the brain where the memories are stored. If they were really gone, Peter's healing ability would have been of no use.

Yes i understand that, but how did he trigger his memories?

Adam didn't trigger his memories, Peter did it himself.

We should not say the Haitian damages or destroys memories as this will lead to inaccurate theories in the future. We only know that he somehow meddles with them. However, I think it is more accurate to assume he blocks synaptical junctions (or disjoints them) in some way. A chemical inhibitor would be a possibility.

He kinda disrupts people's powers too by focusing on them it seems- so a bit closer he could disrupt things a bit more complex than a major new brain function that has to light up like a Christmas tree when they use their powers. This also explains Mrs. Bennets issues with being brain wiped so much. In a way he is really causing brain damage and I guess there are only so many synapses in the brain for memory(sure a lot- but changing the flow of one pipe in hundreds can still screw something up), blocking or disrupting them so many times probably has some, lasting effects ^^;

Adam told Peter to think about what matters most to him, Peter looked at the picture of him and Nathan, Adam tells him his brothers name is Nathan. BAM. As soon as Peter hears the name Nathan, it all starts coming back to him...so I would say that Adam used Nathan to trigger the memories.

Way back when the Haitian decided not to wipe Claires memory, I wondered if it were even possible, give her regeneration. I figured it would ,at least, be a good excuse if her dad caught on to her remembering too much.

It's also likely that he knew his power wouldn't work completely on Claire, since Adam knew about the Haitian and that he could heal from it, It stands to reason that they may have tried to use the Haitian on Adam at one point.

The regeneration might actually require the persons body to attempt to use something for that damaged part to maximize the healing. Thats one way to explain why Peter thinking about his lost memories and healing to regain them, much like Claire "willed" her toe to grow back- possibly causing it to grow back quicker than it would have on its own, possibly.

I tend to agree with this, remember Mrs. Bennet, so many whipes almost screwed her brain, she even got almost in a comma. So is not far fetched to say he do something to the part of the brain that control memory.