This study will investigate the validity of the HOGAR EEG/PSG monitoring kit designed by Bitbrain as a tool for characterizing and assessing cognitive function in older adults, as well as for detecting and predicting cognitive decline. The kit consists of two EEG headbands and a mobile computing device that allows measurements of sleep patterns (PSG) and brain activity (EEG) in a home environment.

The sample includes 500 participants with various degrees of cognitive impairment according to standard clinical criteria, confirmed through an assessment of cognitive status in the laboratories of Bitbrain and the Miguel Servet Hospital in Zaragoza. This assessment includes an introductory session to the study and two cognitive assessment sessions lasting approximately 2 hours each. The first session includes the explanation of the study protocol, the signing of the informed consent, a short cognitive evaluation using screening tests, and the acquisition of blood samples. The second session includes a recording of brain activity using a versatile semi-dry EEG device (Bitbrain, Spain) under resting conditions and the second part of the battery of cognitive evaluations. During the second session, the battery of cognitive and behavioral tests will be completed.

Outside the hospital environment, participants will receive an in-person tutorial and then take the HOGAR biosignal acquisition kit home for 2 days to collect physiological activity in their daily environment. Each day, they will record EEG in resting conditions and PSG during sleep, both self-administered or with the assistance of a family member. This includes the use of the devices Ikon and Ikon Sleep (Bitbrain, Spain) with a Microsoft Surface with user-friendly software.

This cross-sectional study will allow for the examination of correlations between EEG and PSG acquired in participants' homes with all standard tests in a laboratory setting (especially tests for cognitive decline analysis), and specifically their predictive capacity using artificial intelligence tools. Subsequently, a longitudinal follow-up will explore the possibility of predicting cognitive and behavioral decline based on biosensor measurements in the home environment.

General Inclusion Criteria:

• Native Spanish speaker.
• Agree to the examination procedures and tests.
• Ability to involve a close family member or friend for functional evaluation.
• Normal or corrected-to-normal color vision.
• No medical condition requiring chronic systemic medication with psychoactive effects causing confusion.
• No severe psychiatric (according to DSM-V) or neurological diseases (epilepsy with frequent seizures (>1/month) in the last year, multiple sclerosis, etc.).
• No diseases that may interfere with cognitive functions (renal insufficiency on hemodialysis, liver cirrhosis, chronic pulmonary disease with oxygen therapy, solid organ transplant, fibromyalgia, active cancer under treatment).
• No severe hearing and/or visual impairments, neurodevelopmental, or psychomotor disorders.
• No brain injuries that may interfere with cognitive functions (history of traumatic brain injury with parenchymal injury or macroscopic ischemic stroke of large extra-axial vessels or hemorrhagic stroke, brain surgery, brain tumors, or other causes that could result in acquired brain damage such as brain chemotherapy or radiotherapy).
• No treatment with antipsychotic agents in the 6 months prior to the initial assessment.
• No medical condition requiring chronic systemic medication with psychoactive effects causing confusion. No psychiatric or neurological medication.
• No alcohol or drug abuse.
• No serious health problems in the last 12 months (especially neurological or cardiac disorders).

Inclusion Criteria 'Mild Dementia' group:

• Diagnosis of Alzheimer's type dementia, based on a clinical and cognitive assessment conducted by a physician.
• Diagnosis of vascular or mixed type dementia, based on a clinical and cognitive assessment conducted by a physician.
• Lack of autonomy in: 1. basic activities according to the Barthel Index; 2. instrumental activities according to the Lawton Index. Both indices assess dependence associated with the diagnosis of dementia, distinguishing it from the diagnosis of mild cognitive impairment.

Inclusion Criteria 'Mild Cognitive Impairment' group:

• Diagnosis of mild cognitive impairment, based on a clinical and cognitive assessment conducted by a physician.
• Preserved autonomy in: 1. basic activities according to the Barthel Index; 2. instrumental activities according to the Lawton Index. Both indices assess dependence associated with the diagnosis of dementia, distinguishing it from the diagnosis of mild cognitive impairment

Inclusion Criteria 'Subjective Cognitive Decline' group:

• Adherence to SCD-I criteria.
• Attendance at primary care consultation with memory complaints lasting more than 6 months.
• Absence of a diagnosis of mild cognitive impairment or dementia.
• Onset of subjective cognitive decline in the last 5 years.
• Concerns related to subjective cognitive decline (not associated with an acute event) expressed by the participant and/or an informant.
• Cognitive performance within the normal range on cognitive tests (MMSE (Mini Mental State Exam) < 26 / MIS (Memory Impairment Screen) < 6).
• No severe depressive symptoms, indicated by scores > 17* on the 30-item Geriatric Depression Scale.

Inclusion criteria No impairment group:

• Cognitive performance within the normal range on cognitive tests (MMSE < 26 / MIS < 6).
• Absence of a diagnosis of mild cognitive impairment or dementia.
• Not meeting the criteria for SCD-I [21].
• Independent person living in their own home.
• No subjective memory complaints.

Our goal is to assemble a diverse sample representing different cognitive impairment levels to validate our developed home kit for effective quantification and prediction of decline. The sample comprises four groups categorized by cognitive level, aiming for gender and age balance.

1. MILD DEMENTIA: Diagnosed individuals (150) with mild dementia (GDS 4 or CDR 1). Moderate and severe cases (GDS 5-7) are excluded, including Alzheimer's, vascular, or mixed dementia.
2. MILD COGNITIVE IMPAIRMENT: Diagnosed patients (150) with mild cognitive impairment (GDS 3 or CDR 0.5).
3. SUBJECTIVE COGNITIVE DECLINE: Individuals reporting memory complaints (100) without objective impairment (GDS 2 or CDR 0).
4. NO IMPAIRMENT: Individuals without cognitive issues (100), serving as a control group (GDS 1 or CDR 0). Balanced recruitment from family members or advertisements.