In the current study, the investigators will examine the extent of subclinical epileptic activity in patients with Alzheimer's disease and patients with Lewy body dementia as compared to healthy elderly controls. The participants will wear a new device called "ear-EEG", which makes it possible to record EEG for longer periods of time while at home. Furthermore, the investigators want to investigate whether there is an association between subclinical epileptic activity and the cerebral blood flow as measured with functional MRI.

Inclusion Criteria (Alzheimer's disease):

• Meet the criteria for probable Alzheimer's disease with amnestic presentation as described in the NIA-AA criteria (McKhann 2011)
• The diagnosis has been made by either a neurologist, psychiatrist or a geriatrician at the memory clinic at Rigshospitalet or Zealand University Hospital
• The participant is between 50 and 90 years old
• The MMSE score is between 16-28
• The participant does not wear a hearing aid
• The participant is a native Danish speaker
• The participant has at least attended school for 7 years
• The participants' hearing and vision is sufficient to participate in neuropsychological tests
• The participants' general condition of health allows that the participant can cooperate with the trial
• The participant does not suffer from psychiatric diseases (except mild depressive symptoms or mild depression) or neurological diseases that affect the brain other than Alzheimer's disease
• The treatment with anti-dementia medication or SSRI drugs have been given in stable dose for at least 3 months up to the inclusion and the doctor including the participant estimates that treatment will not change within the next 6 months
• No overuse of alcohol or intake of illegal drugs within the last 2 years
• The participant has previously undergone a CT or MRI scan, which is compatible with Alzheimer's disease
• The participant does not have any contraindications for MRI or MRI contrast
• The participant is living with another person, who is willing to take part in the trial, and who is together with the person long enough to observe the behavior (if any epileptic activity should arise)

Exclusion Criteria (Alzheimer's disease):

• Diagnosis of epilepsy prior to the diagnosis of Alzheimer's disease was made
• Other focal pathology in the hippocampus for example hippocampal sclerosis
• The person living with the participant is not able to participate (e.g. due to a serious disease or disability) in the clinical visits or able to register behavior suspected of epilepsy
• The participant is living in a nursing home
• The participant is treated with antiepileptic medication, tricyclic antidepressants or antipsychotics
• Daily or nearly daily intake of medication known to have an anticholinergic or an adrenergic effect, which is suspected to affect the cognitive abilities or the EEG
• Large brain infarctions or more than 4 lacunar infarcts
• The participants is suffering from uncontrollable movements of the face as for example oral dyskinesia

Inclusion Criteria (Lewy body dementia):

• Meet the criteria for Lewy body dementia as described in dementia with Lewy body consortium (McKeith 2017)
• The diagnose has been made by either a neurologist, psychiatrist or a geriatrician at the memory clinic at Rigshospitalet or Zealand University Hospital
• The participant is between 50 and 90 years old
• The MMSE score is between 16-28
• The participant does not wear a hearing aid
• The participant is a native Danish speaker
• The participant has at least attended school for 7 years
• The participants' hearing and vision is sufficient to participate in neuropsychological tests
• The participants' general condition of health allows that the participant can cooperate with the trial
• The participant does not suffer from psychiatric diseases (except mild depressive symptoms or mild depression) or neurological diseases that affect the brain other than Lewy body dementia
• The treatment with anti-dementia medication or SSRI drugs have been given in stable dose for at least 3 months up to the inclusion and the doctor including the participant estimates that treatment will not change within the next 6 months
• No overuse of alcohol or intake of illegal drugs within the last 2 years
• The participant does not have any contraindications for MRI or MRI contrast
• The participant is living with another person, who is willing to take part in the trial, and who is together with the person long enough to observe the behavior (if any epileptic activity should arise)

Exclusion Criteria (Lewy body dementia):

• Diagnosis of epilepsy prior to the diagnosis of Lewy body dementia was made
• Other focal pathology in the hippocampus for example hippocampal sclerosis
• The person living with the participant is not able to participate (e.g. due to a serious disease or disability) in the clinical visits or able to register behavior suspected of epilepsy
• The participant is living in a nursing home
• The participant is treated with antiepileptic medication, tricyclic antidepressants or antipsychotics
• Daily or nearly daily intake of medication known to have an anticholinergic or an adrenergic effect, which is suspected to affect the cognitive abilities or the EEG
• Large brain infarctions or more than 4 lacunar infarcts
• The participants is suffering from uncontrollable movements of the face as for example oral dyskinesia

Inclusion Criteria (Healthy controls):

• Normal cognition as evaluated at the clinical examination
• The participant is a native Danish speaker
• The participant has at least attended school for 7 years
• The participants' hearing and vision is sufficient to participate in neuropsychological tests
• The participants' general condition of health allows that the participant can cooperate with the trial
• The participant does not suffer from psychiatric diseases (except mild depressive symptoms or mild depression) or neurological diseases that affect the brain
• The participant does not have any contraindications for MRI or MRI contrast

Exclusion Criteria (Healthy controls):

• The participants is suffering from uncontrollable movements of the face as for example oral dyskinesia
• The participant is suffering from epilepsy or receives anti-epileptic medication

In the first part of the study (feasibility), the investigators will include 10 patients with Alzheimer's disease from the memory clinics at Rigshospitalet and Zealand University Hospital - Roskilde. In the main study, the investigators will include an additional 40 patients with Alzheimer's disease, 20 patients with Lewy body dementia, and 50 healthy controls.