Implants deep in the brain are used to send in signals directly in stimulation. The most common application is to manage Parkinson's disease, i.e., tremors and bradykinesia. But there are serious efficacy problems with deep brain stimulation, related to the discrepancy in adapting a relatively simple mechanical device to the complexity of the brain's neural wiring. Major safety concern is the risk of brain infections after the implant procedure and cranial trauma can dislocate an implant with an obvious amplification effect on the extension of associated brain injuries. Another important concern is that brain implants are basically electrical devices, so there is a risk of interference in the action of these implants by electromagnetic fields generated by other sources.
Deep brain stimulation has been used to treat psychiatric diseases such as chronic depression, and brain implants have been advocated for correcting behavioural traits and/or enhancing cognition-related brain functions in normal subjects. But mainly they are effective in treating serious motor dysfunctions where quality of life is at stake, the dignity of persons and their sense of independence and privacy as opposed to being constantly dependent on carers and family members.