PROJECT SUMMARY/ABSTRACT There are limited treatment options for Alzheimer’s disease dementia (AD) and its associated progressive cognitive impairment, calling for target interventions that potentially slow the progression of cognitive decline, prevent, or delay the onset of AD in individuals with mild cognitive impairment (MCI). One promising treatment possibility is auditory stimulation at gamma frequencies. Emerging research suggests that 40 Hz sound may stimulate gamma oscillations and enhance cognitive function in older adults, but much remains unknown. Our group has created a novel 40 Hz music intervention, which may provide similar gamma entrainment, and is likely more aesthetically pleasing, allowing an evaluation of the long-term use of 40 Hz stimulation on cognitive function. We will conduct a 3-treatment 3-period pilot crossover trial to test the feasibility and preliminary efficacy of 40 Hz music (Condition A), 40 Hz sound (Condition B) and preferred music (Condition C) on neural gamma activity and cognitive function in 30 community-dwelling older adults with amnestic MCI. The participants will be randomized to three groups with different sequences of exposure to all three conditions. To examine the effect of the three conditions on gamma entrainment, participants will first undergo an acute music/sound stimulation session and a scalp electroencephalogram (EEG) will be recorded during the session. Next, the participants will be instructed to listen to the assigned sequence of conditions, with each condition for four weeks (1 h/day, 5 days/week). There will be a 10-day wash-out break between each condition. Semi- structured interviews will be conducted after completing each condition. The specific aims are as follows: Aim 1: Evaluate the feasibility of the study and the three conditions: 40 Hz music, 40 Hz sound, and Preferred Music in older adults with MCI. Qualitative data will be used to understand the participant's experience and acceptability of the three conditions; Aim 2: Determine the preliminary efficacy of 40 Hz music for four weeks on cognitive function compared with 40 Hz sound and Preferred Music; Aim 3: Evaluate the effect of 40 Hz music and 40 Hz sound on gamma entrainment during the acute stimulation session. This study will be the first to test the feasibility and preliminary efficacy of innovative 40 Hz music and 40 Hz sound interventions on cognitive function in older adults with MCI, a high-risk population for AD. Findings from this study will provide important evidence for future development, selection, evaluation, and implementation of music/sound interventions for cognitive health in older adults with MCI.