Yes, the human brian can and does permanently lose information. Memory is stored in the patterns of neural connections; when those connections are lost through traumatic disruption or because of the death of too many of the neurons involved, the memories which had been stored are gone. This is why people who have suffered traumatic brain injury usually permanently lose at the least the period of time directly before the accident, and why those people suffering from senile dementia never regain the memory they lose. Memories are not often stored in only a single location, however; they are often stored in connections spread widely across the brain. So trauma to only a small part of the brain can disrupt memory, but the brain will try to reconstruct the connections lost using healthy cells, essentially resulting in reconstructed memory. Even healthy memories are often reconstructed in such a fashion over time, with every time you hash over them resulting in some new neural connections being made and some old ones lost. Information storage in the brain is highly inexact and volatile. There are exceptions. There are some mutations which seem to result in permanent, rather than long term or transitory, connections being made; once a neuron makes a connection to a neighboring neuron, that connection will be there for the lifetime of the individual, and the patterns of firing which encode memory are retained forever. These are the individuals born with "photographic memory", and it is a real phenomenon. However, having spoken to a test subject with complete photographic memory (he could recite the page of a geology textbook which he had seen only once, and had it word-for-word perfect 4 months after seeing it), he described it as being hell-on-earth, a very uncomfortable thing to live with. "40 years of every embarrassing moment I have ever had, 40 years of bowls of cornflakes for breakfast, 40 years of going to the bathroom or sitting in traffic..." -- this is information that the normal human just doesn't retain. Those connections are seldom important enough to be long-term, unless they were formed in proximity to a very emotional event -- some neurotransmitters can "fix" neural connections. I hope that gives you a better idea.