Chapter 44 Preconscious auditory processing in coma

Publisher Summary Coma is a state of apparently absent or suspended consciousness, complicating various clinical conditions, for example, circulatory arrest or head trauma. In recent times, interest is growing in the assessment of coma and in predictors of awakening and recovery. With respect to auditory evoked potentials short-latency responses (BAEPs) that explore the brainstem and middle-latency responses (MLAEPs), exploring the primary auditory cortex, have been used more often than late auditory evoked responses. It is only recently that event-related potentials (ERPs) have been studied in comatose patients. The use of P300 in comatose patients is questionable, as it is closely related to attention and decision-making. Recording mismatch negativity (MMN), in comatose patients, is more suitable, as it can be elicited in the absence of attention— that is, when no task performance is required —and it is best recorded in conscious subjects, using a passive condition in which attention is directed away from the auditory stimulation. The MMN is mainly generated by the auditory cortex. It depends on the presence of a memory trace formed by the preceding standard stimulus. The chapter describes and discusses the procedure and the result, respectively, of a few studies in detail that have dealt with MMN recording results in comatose patients.