Auditory Evoked Potentials Across Cognitive States: Awake, Sleep, Sedation, and Anesthesia

Auditory evoked potentials (AEPs) comprise a family of electrophysiological responses that follow acoustic stimulation from the auditory nerve and brainstem to thalamocortical and association networks. Their interpretive value lies in the combination of millisecond temporal resolution and hierarchical sensitivity: early responses mainly index the fidelity and timing of ascending sensory conduction, whereas later responses increasingly depend on cortical context, attention, prediction, and behavioral relevance. This review develops a state-aware framework for interpreting AEPs during wakefulness, natural sleep, pharmacologic sedation, general anesthesia, and impaired consciousness. We first describe the ascending auditory pathway and relate approximate latency ranges to distributed neural generators. We then examine how attention and task engagement modify early cortical processing; how non-rapid eye movement and rapid eye movement sleep preserve some forms of acoustic analysis while reorganizing or suppressing others; and how anesthetic effects vary with response latency, drug concentration, and cortical hierarchy. The review also distinguishes transient event-related potentials from steady-state auditory evoked potentials (SSAEPs), and explains why phase-locked activity can be recovered by trial averaging whereas non-phase-locked induced activity requires single-trial time-frequency analysis. Separate sections address cross-species translation; click, chirp, oddball, steady-state, and naturalistic speech paradigms; as well as clinical applications in hearing assessment, intraoperative monitoring, anesthesia, and disorders of consciousness. The central conclusion is that an AEP is interpretable only when its generator, stimulus, analysis domain, recording conditions, and cognitive state are considered together.