The Ministry of Magic had a mysterious Brain Room, but its purpose was never completely made clear in Harry Potter. The room was housed in the Department of Mysteries and was featured in Harry Potter and the Order of the Phoenix. Unfortunately, several of the mysterious rooms within that area of the Ministry of Magic didn't get enough focus, according to fans of the franchise.
The Department of Mysteries was located on the ninth level of the Ministry of Magic, the governing body of the wizarding world located in London. The department was top-secret and nearly impossible to get into. It was where the Ministry studied some of life's greatest mysteries, hence the name. Among the department was the Hall of Prophecy, Death Chamber, Love Chamber, Space Chamber, Time Room, and of course, the Brain Room. The chambers also happened to be the setting of a key battle during the Second Wizarding War.
In Order of the Phoenix, Lord Voldemort lured Harry and members of Dumbledore's Army to the Department of Mysteries to obtain a prophecy. Harry and his friends were ambushed by Death Eaters so they fled through various rooms within the department before the Order of the Phoenix arrived to help them. Upon entering the Brain Room, the group described a long, rectangular chamber that housed a tank full of white brains swimming in a green substance. As Ron learned first-hand, when the brains were removed, their tendrils or "feelers" could attack and injure bystanders. The explanation behind the brains was never given, but their inclusion in the mysterious department made sense.
The Ministry Of Magic's Brain Room Wasn't Seen In The Movies
Like most of the chambers in the Department of Mysteries, the Brain Room wasn't seen in the film adaptation of Order of the Phoenix, nor did it appear in any other installments. Though these rooms were omitted from the films, scenes were shot for the Battle of the Ministry of Magic sequence before they were cut from the theatrical release. The Brain Room, however, remains intriguing since it revealed that the Ministry was studying thought and the powers of the mind. The entire department proved that the wizarding world was just as curious about abstract concepts compared to muggles. Whether it was death, love, time, or the mind, there were still many answers to uncover.
It could have been possible that J.K. Rowling had a larger plan to dive back into the Brain Room, or other chambers in the department, in future installments but decided to go in other directions. The Brain Room had a room that directly led to the Death Chamber, implying that there was a study between death and consciousness. There was also a belief that the tank held the brains of some of the wisest and recognized wizards to assist in their studies. In addition, some would argue that the brains helped in Legilimency was heavily used in the studying of the mins. Legilimency in Harry Potter was explained to be the act of using magic to navigate someone's mind and interpreting their feeling, aka mind-reading. Until Rowling reveals otherwise, the mystery behind the Brain Room remains.