Mild cognitive impairment (MCI) refers to early-stage memory or cognitive ability loss. The Alzheimer’s Association explains that people with MCI may or may not develop dementia, and that:

“for neurodegenerative diseases, MCI can be an early stage of the disease continuum, including for Alzheimer’s if the hallmark changes in the brain are present.” 

A recently published study in the Journal of Alzheimer’s Disease sought to understand the relationship between serotonin levels, amyloid-β (Aβ) deposits in the brain, and mild cognitive impairment. According to Kristen Crocker of Futurity, the research team evaluated PET scans from 45 healthy individuals and 49 individuals with mild cognitive impairment. 

Study Findings

The findings show that people with MCI had 25% lower serotonin transporter levels in the cortical and limbic region of the brain. Serotonin transporter is a protein that transports serotonin (a neurotransmitter) from synaptic spaces to neurons in the nervous system.

Since serotonin is known to be a natural mood enhancer, lower levels of serotonin can correlate with depression or other mood issues. In addition to lower serotonin levels, people with MCI also had higher Aβ levels. Researchers have long believed that Aβ is related to depression; many hypotheses suggest that Aβ deposits play a role in Alzheimer’s development and progression. 

Ultimately, the research highlights how people with mild cognitive impairment are already experiencing lower serotonin and neurodegeneration in areas of the brain that play a role in emotions, memory, and executive function. 

However, it’s important to recognize that this study does not show a causative relationship between low serotonin and Alzheimer’s disease development. The study does not show that lower serotonin enhances the progression from mild cognitive impairment. Future research could explore topics such as whether targeting serotonin could improve cognition, as well as how serotonin and Aβ levels change over a longer period of time in people with MCI. 

Read more about the study over at Futurity.

About Alzheimer’s Disease 

Alzheimer’s disease, affecting 55 million people worldwide, is a neurodegenerative disorder and the most common form of dementia. Doctors still don’t know the exact cause of Alzheimer’s disease. It’s believed to result from a combination of environmental factors, genetics, and lifestyle choices. If you are female, older, have prior head trauma or a family history of Alzheimer’s disease, or have poor sleeping and exercise habits, your risk of Alzheimer’s disease is heightened. 

As brain cells degenerate and die, people with Alzheimer’s disease experience stages of progressively worsening symptoms. Signs of this disorder can include:

• Memory loss that disrupts daily life
• Difficulty planning, solving problems, or making judgments or decisions
• Confusion with times or places
• New issues with language or vocabulary, speaking, or writing 
• Loss of preserved skills, such as the ability to play a musical instrument or drive a car
• Changes in mood, behavior, or personality such as anger, aggression, social withdrawal, delusions, or loss of inhibitions
• Complications such as aspiration, pneumonia, infections, malnutrition, and dehydration