Local anesthesia is only temporary interruption of nerve conduction at the surgical site. In this way, pain can not be transmitted to the brain, people can not feel pain. It is usually used for short operations, or for examinations that may cause pain.
but local anesthesia is not enough to block the pain if the operation takes a long time or involves a large area and many nerves. It’s safer to use general anesthesia at this time.
but both local anesthesia and general anesthesia will not damage the brain, let alone IQ. After a period of time, it will be naturally metabolized, almost no negative impact on the body.