Neuralyzer

A neuralyzer, sometimes spelled as neuralizer, is a device seen in the Men in Black franchise. It is one of the signature tools and considered standard issue employed by the Men in Black. It is a device about the size of an average cigar tube that gives a bright flash which erases the memories of the past hours, days, weeks, months or years, depending on the chosen settings. It first appeared in the first issue of the comic book series, and has appeared in all three films, as well as the animated TV series. It also has changed from red to blue.

The device in the comic books was referred to as a 'neurolyser'. This is also where the concept of using Ray-Ban sunglasses was introduced. It is seen more in the shape of a flashlight than a cigar-like shape made popular by the films. It does not simply erase memory like the movie counterpart does, but is a device used for manipulation and control. When neurolysed, a witness is simply hypnotized and does what ever Agent K or J wants them to do, such as provide information, believe a lie and/or pass that lie along as fact.

"This is called a neuralyzer. It's a gift from some friends from out of town. This red eye here will isolate the electronic impulses in your brains, more specifically the ones for memory."

A neuralyzer wipes the memory of a target or witness, putting them under a hypnotic state, making them susceptible to suggestion and implantation of false memories, used by MiB as a moral substitute to witness elimination by murder while still retaining their existence or/and alien presence on Earth unknown to the public. The length of memory erased can be changed using buttons and dials. There are different neuralyzer models with different button and dial configurations. These buttons or dials can be set accordingly to the amount of time needed to be forgotten, and it can be set to minutes, hours, days, months and years. The device produces a noisy, camera-like flash. The agents implant new memories in place of the old ones.

In order for the agents to not be affected by the flash, they wear Ray-Ban super dark sunglasses that reflect the rays. After being neuralyzed, the agents have about 30 seconds to supply new memories to replace the ones they've just erased. If there are more witnesses to neuralyze, or if they are pressed for time, a special team is sent in to supply memories. The obvious flaw of the neuralyzer is that it can't delete a specific desired memory but only can erase all memories of a certain time period starting from the point when it's used, so, if a memory from an earlier time period has to be erased, so do all memories following that specific memory right to the point of the usage.

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Wikipedia