Brain waves for automatic biometric based user recognition

Brain signals have been investigated within the medical field for more than a century to study brain diseases like epilepsy, spinal cord injuries, Alzheimer’s, Parkinson’s, schizophrenia, and stroke among the others. They are also used in both brain computer and brain machine interface systems with assistance, rehabilitative, and entertainment applications. Despite the broad interest in clinical applications, the use of brain signals has been only recently investigated by the scientific community as a biometric characteristic to be used in automatic people recognition systems. However, brain signals present some peculiarities, not shared by the most commonly used biometrics, like face, iris, and fingerprints, with reference to privacy compliance, robustness against spoofing attacks, possibility to perform continuous identification, intrinsic liveness detection, and universality. These peculiarities make the use of brain signals appealing. On the other hand there are many challenges which need to be properly addressed. Among them, the understanding of the level of uniqueness and permanence of brain responses, the design of elicitation protocols, the invasiveness of the acquisition process are only few of the challenges which need to be tackled. In this paper we further speculate on those issues which represent an obstacle towards the deployment of biometric systems based on the analysis of brain activity in real life applications and intend to provide a critical and comprehensive review of state-ofthe- art methods for electroencephalogram based automatic user recognition, also reporting neurophysiological evidences related to the performed claims.