Methamphetamine neurotoxicty is thought to have three causes, although none have been conclusively demonstrated to be a thing because no-one's done really convincing research on this topic.
- damage to dopamine receptors and reuptake. Not really an issue unless you use it regularly, heavily and/or long term. The long term negative impacts related to mood reported by many chronic users are most likely caused by this aspect.
- overheating. Extended raised body temperature caused by anything can kill brain cells. Becomes more of a risk the longer your sessions. Harm reduction tips include staying cool and not physically exerting yourself too much.
- serotonin receptors forced to take in dopamine instead of serotonin. These receptors aren't great at breaking down dopamine, so they produce even more neurotoxic substances when they do so. There are other drugs that do this significantly more than methamphetamine, though, so this is of biggest concern to people who are particularly sensitive to changes in their serotonin production and reuptake.
What exactly are you wanting to know? Are you having some symptoms you're worried about?