Memories can be extracted from a person's mind and reviewed, from an outside point of view, in a pensieve. These memories appear as silver, hair-like wisps, and can be stored in bottles. Extracted memories can be altered, as Horace Slughorn attempted to do to a memory he gave to Albus Dumbledore in the 1996–1997 school year, although such alterations leave noticeable flaws in the recollection. A fragment of Lord Voldemort'ssoul was able to show his memories through the power of his diary, rather than the need of extracting it and placing it into a pensieve.
Internal viewing
Memories can be read without the needs of extracting them, through the powers of Legilimency. Also, Veritaserum works based on the memories of the person, and if there are any alterations done to such memories, they would speak what they assume to be the truth, not the truth that has been suppressed. Occlumency, the art of suppressing such memories and thoughts, is a way to counter the two aforementioned methods.
External interference and damage
Memories can receive external interferences such as the Memory Charm or False Memory Charm, which can suppress certain memories or create fake ones, respectively. Such alterations may cause permanent memory damage if done at great intensity or incorrectly, as Gilderoy Lockhart and Bertha Jorkins both suffered severe amnesia that was irreversible. When Lord Voldemort forcibly broke through the Memory Charm on the latter, she remembered all of the things that were suppressed, but at the price of her body and mind suffered damage far beyond repair. Such alterations can also be bypassed such as when Dumbledore extracted a true memory over a false one in Morfin Gaunt, though he noted it to be a difficult task. In a related matter, one's memories may be improved through a Memory Potion, Baruffio's Brain Elixir and powdered dragon claw.
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