Event-related potentials (ERPs) are brain potential changes associated with certain mental activities (i.e., events) that reflect changes in the neurophysiology of the brain during cognitive processes. The components that have been extracted are P300 , N270 , N400, mismatched negative wave (MMN), and correlated negative variation (CNV). Among them, MMN is an endogenous event-related potential component, reflecting the automatic processing of information in the brain, which is increasingly used in clinical and scientific research without the active participation of subjects, and is also a research hotspot for ERPs. MMN was first reported in 1978 by Ntnen et al. and was shown to be induced by “deviant” stimuli that randomly appear in a repeated sequence of “standard” stimuli. Unlike the P300, the MMN can appear clearly under non-attentive conditions with a latency of 100-250 ms, reflecting the automatic processing of information in the brain that does not follow the subjective will of the person, and is an important tool for objective evaluation of auditory recognition and sensory memory. The mechanism of MMN: A large number of studies have shown that the MMN reflects the sensory memory mechanism of auditory information, in which a memory trace is formed in a specific part of the brain when a standard stimulus is repeated, and then a new stimulus is compared with the memory trace. Therefore, giving deviant stimuli alone does not produce MMN , so a pseudo-random arrangement of the stimulus sequence is required: the first deviant stimulus appears after multiple standard stimuli. The origin of the MMN is thought to be in the temporal auditory cortex and its adjacent areas.Kropotov et al. found that area 41 is particularly sensitive to changes in sound frequency, suggesting that neuronal circuits in this area are primarily responsible for the analysis of sound features, whereas the ERP recorded in area 42 is clearly influenced by the stimulus rate, and it is possible that this area is primarily responsible for the formation of memory traces, with specific responses to deviant stimuli In contrast, the ERP recorded in area 42 is clearly influenced by the stimulus rate, and it is possible that this area is mainly responsible for the formation of memory traces and specific responses to deviant stimuli are recorded in auditory association cortex (area 22). In summary, MMN abnormalities reflect abnormalities in central auditory processing and are the only objective assessment of sensory memory available. Because brewing dizziness can be produced in an unconscious state, it provides a better objective measure for patients who have difficulty cooperating with conventional examinations, and is important for the diagnosis of cognitive impairment in psychiatric and neurological intensive care patients. Currently MMN has been widely used in the early diagnosis of Alzheimer’s disease, Parkinson’s, schizophrenia, anxiety and depression. From the characteristics of MMN, we can easily find that it is produced in a non-attentive unconscious state, indicating that it reflects automatic processing in the brain that does not shift with the subjective will of the person, and is a product of higher cognitive discrimination functions. For those comatose patients in the early stages of recovery of consciousness, when the existing clinical examination methods are unable to detect these weak conscious activities, the MMN may have already appeared by this time, which is significant for early evaluation of the prognosis of patients with consciousness disorders and for more active treatment methods! found that the MMN wave amplitude and latency correlated with the degree to which the patient regained consciousness, and that as consciousness returned, the MMN wave amplitude increased, as did the ability to process abnormal sound stimuli. This study suggests to us that if a comatose patient can be monitored for MMN, there is a good chance that he will be able to regain consciousness in the future! Since last year, four patients have been tested so far. The picture below shows a patient with a large cerebral infarction who had not recovered consciousness significantly after a period of treatment and whose family had lost confidence in continuing treatment. After the MMN test, it was found that MMN could appear after giving sound stimulation, which proved that the patient had conscious activity.