Does Growing New Neurons Improve Memory?

Post by Rebecca Glisson

The takeaway

Recent studies have shown that humans can grow new neurons (neurogenesis) even as adults. Individuals with Alzheimer’s disease have much lower neurogenesis than normal, while older adults with high cognitive capacity have abnormally high neurogenesis.

What's the science?

It was long thought that adults do not grow new brain cells (neurogenesis), but more recently, we have come to understand that neurogenesis happens throughout our lives. Most studies use rodents as a model for human brains, which doesn’t yield enough insight into how neurogenesis occurs in adult humans. This week in Nature, Disouky and colleagues studied the brains of humans at all ages, with and without Alzheimer’s disease, to better understand the link between neurogenesis and cognitive functioning.

How did they do it?

To study neurogenesis in humans, the authors used the brains of deceased donors. The donors were groups of individuals at different ages and cognitive abilities, including young and older adults with normal cognitive ability, individuals who had or were starting to show signs of Alzheimer’s disease, as well as adults they called “SuperAgers”, or individuals who had high memory test scores. The authors identified neurogenesis from the genetic sequence present in cells in the hippocampus, a part of the brain involved in memory, using a method called RNA-seq. Cells that have just grown, immature cells, have a specific genetic sequence that the authors analyzed to determine how much neurogenesis had occurred.

What did they find?

Both younger and older adults with healthy cognitive ability had high levels of neurogenesis in their hippocampi. In contrast, individuals with Alzheimer’s disease or symptoms of it had less neurogenesis and fewer immature neurons. This suggests that the slowing of neurogenesis may impact memory in diseases such as Alzheimer’s. One interesting result was that the “SuperAger” adults had significantly more neurogenesis and more immature neurons than any other group, including the healthy adults, suggesting that neurogenesis may help support healthy cognitive functioning as we age. 

What's the impact?

This study is the first to analyze the sequence of new immature neurons in humans and the first to link neurogenesis to cognitive function in individuals of different age groups and cognitive ability. Studies like these can help us better understand mechanisms of memory preservation or memory decline and how to develop better preventative care and treatment for those impacted.

Access the original scientific publication here.

Reducing Loneliness: Comparing an AI Chatbot to a Human

Post by Lila Metko

The takeaway

Given the global loneliness epidemic, many scientists are looking to technology to find scalable solutions. A recent study shows that artificial intelligence (AI) may be a good solution when an immediate boost in affect is needed, but that over the long term, real human relationships can better foster a reduction in loneliness.

What’s the science?

Generative AI is used by a large number of people not just for information, but for a meaningful source of connection. In recent years, a growing number of scientific studies have examined the effects of chatbots on social connection and positive mood. While many studies have shown positive immediate effects of chatbots, few have assessed the benefits over time. Interestingly, one long-term study found that chatbots may negatively impact emotional state, with seeking chatbot social support predicting increased loneliness. This week in Journal of Experimental Social Psychology, Li and colleagues assessed the cumulative impact of interacting with a custom AI chatbot on emotional outcomes in a population vulnerable to loneliness.

How did they do it?

The authors conducted this study using two experimental groups (chatbot and human) and one control group (daily journaling) to compare the impact of a supportive chatbot on loneliness with that of conversing with a random peer. They conducted this two-week study using a custom chatbot named Sam, designed to have the qualities of an ideal supportive friend, and a subject pool of first-semester college students at a Canadian university. Conversations for each group, including the journaling group, were held on the social media platform Discord, a popular platform among students. The human peer group met with their human conversation partners in person at the beginning of the study. The chatbot and peer group participants were asked to send one meaningful message each day. Each participant was asked to perform their assigned task and take a short survey for 14 consecutive days. The participants were also assessed via a survey pre and post-study.

What did they find?

The authors found that only the human peer group showed a decrease in loneliness post-study. A similar pattern was found for positive mood and perceived isolation. Interestingly, both the human peer group and the chatbot group displayed decreased negative mood post-study compared to the control group. Participants were allowed to use their Discord room for one week following the study. The percentage of the human peer group that continued to engage with their human conversation partner in the Discord room was more than double the percentage in the group that continued communication with their chatbot during this one-week time period. These findings overall suggest that interactions with a human peer may be more beneficial than interactions with an AI chatbot to reduce loneliness.

What’s the impact?

This study’s results suggest a “middle ground” role of AI chatbots on emotional outcomes in individuals vulnerable to loneliness, demonstrating that a chatbot can reduce negative affect, while a human’s support may have a more positive impact in the longer term. This study sheds light on when to use AI or human-based support in vulnerable populations to reduce loneliness. The authors suggest that it is better to view AI as a tool to ameliorate rather than mimic human connection.

Access the original scientific publication here.

Can Cell Therapy Restore Hearing Loss?

Post by Anastasia Sares

The takeaway

In an experimental cell therapy treatment, researchers transplanted young, immature auditory cells from the ears of newborn mice into older mice whose hearing had been damaged. These cells, surrounded by a new environment, matured and repaired the hearing of the older mice. 

What's the science?

Deep in the inner ear are cells called hair cells that are responsible for taking sound from the environment and turning it into electrical signals to be sent to the brain. These cells are attached to a membrane in the ear that vibrates with incoming sounds, and the movement of this membrane causes the cells to fire. However, as we age, hair cells experience significant wear and tear, and they are sensitive to insults like loud noise exposure, infections, and head trauma. There are even certain classes of drugs that can cause hair cells to die off as a side effect. Hair cells generally do not regenerate in adults, so when they die, it causes an irreversible loss in hearing. While there are some solutions for hair cell loss, such as cochlear implants, these all come with their own drawbacks.

Cell therapy is a kind of medical treatment that involves taking cells from one organism and transplanting them into another (or from one organ/tissue to another within the same organism). It includes treatments like bone marrow transplants and stem cell therapy. When trying to apply this kind of therapy to hearing loss, there are several challenges: will the transplanted cells develop into functioning hair cells? Will the procedure be too invasive and cause additional damage to the inner ear? Will the procedure result in significantly better hearing in the end?

This week in Neuroscience, Liu and colleagues showed that cells can be successfully transplanted into the inner ear and restore hearing function in mice that have drug-induced hearing loss.

How did they do it?

The authors first induced hearing loss in a group of adult mice by administering an antibiotic known to cause hair cell death (kanamycin). Then, relying on previous research, they extracted a very specific type of cell from the inner ears of newborn mice and grew these cells in a gel matrix, where the cells clumped together to form small “organoids” that were ready to become hair cells. They then injected these cells into the left inner ear of each adult mouse (with the right ear serving as a control).

To measure the mice’s hearing, the authors used the auditory brainstem response, which records electrical activity from the brainstem to measure how well the early auditory system responds to sound. They made these measurements before hearing loss, after hearing loss, and after cell therapy.

What did they find?

The authors confirmed that hair cells had died and that the adult mice’s hearing was severely impaired after being exposed to kanamycin. After cell therapy, hair cells survived the transplant and did not cause any additional hearing loss in the mice. The new cells were able to repopulate the inner ear, and hearing thresholds recovered substantially (though not completely) following the cell therapy.

What's the impact?

This study shows that it is possible to restore the function of hair cells and significantly improve hearing using cell therapy. Cell therapy may be a viable way to address the previously irreversible problem of hearing loss that affects millions of people worldwide.

Access the original scientific publication here.