Salk’s Year of Brain Health: Nicola Allen on Brain Inflammation and Lifelong Cognitive Health

Why It Matters

Restoring astrocyte and microglia function offers a promising strategy to mitigate age‑related cognitive decline and Alzheimer’s, potentially extending healthy lifespan for millions.

Key Takeaways

• Brain consists of roughly 50% glial cells, not just neurons.
• Astrocytes regulate neurotransmitter spillover and recycle signals for efficiency.
• Aging impairs astrocyte and microglia function, reducing synaptic connectivity.
• Microglia prune excess connections early; dysfunction contributes to Alzheimer’s.
• Rejuvenating glial cells may restore neuronal communication in older brains.

Summary

The Salk Institute’s "Year of Brain Health" podcast features neuroscientist Nicola Allen discussing how immune health intertwines with cognitive longevity. Allen explains that the brain is roughly a 50/50 mix of neurons and glial cells—astrocytes, microglia, and blood vessels—challenging the traditional neuron‑centric view taught in schools. Key insights include astrocytes’ role in clearing excess neurotransmitters and recycling them for reuse, and their capacity to interact with up to a million synaptic connections. As we age, both astrocytes and microglia lose their regenerative and signaling abilities, leading to diminished synaptic networks and impaired waste clearance. Genetic studies link many Alzheimer’s risk genes to immune pathways, highlighting how dysregulated glial activity can both damage neurons and fail to support them. Allen notes that during development microglia prune surplus neurons, a process that largely ends by age thirty, while astrocytes continually modulate synaptic precision. In Alzheimer’s patients, glial cells adopt harmful immune programs and down‑regulate protective functions, creating a double‑edged problem. She emphasizes that understanding these mechanisms opens avenues to rejuvenate glial cells, coaxing them to restore youthful neuronal communication. The implications are profound: targeting glial health could become a cornerstone of therapies aimed at preserving cognition in an aging population, shifting focus from neurons alone to the broader cellular ecosystem that sustains brain function.

Original Description

When we think about brain health, we tend to think about neurons. But some of the most important work of protecting the brain may depend on immune and other cell types, which make up a surprising 50% of the human brain.

In this special Beyond Lab Walls video podcast episode—part of the Salk Institute’s 2026 Year of Brain Health—Salk President Gerald Joyce, MD, PhD, speaks with Nicola Allen, PhD, a leading neuroscientist whose lab studies how non-neuronal brain cells shape brain function in health, aging, and disease.

Together, they explore:

- Why non-neuronal brain cells have been underestimated for so long

- Astrocytes and their “job description” in a healthy brain

- What changes in the brain’s repair and immune signaling as we age

- The difference between inflammation in the body and inflammation in the brain

- Why chronic inflammation is linked to cognitive decline

- How immune health may help shape Alzheimer’s disease risk and progression

- What it looks like to unite neuroscience and immunology through Salk’s Neuroimmunology Initiative

- Practical, science-informed ways to support immune health for lifelong cognitive strength

This conversation reflects Salk’s commitment to foundational science: asking the questions that reveal how the brain stays resilient—and how we can protect it across the lifespan.

Learn more about Salk’s Year of Brain Health: www.salk.edu/brain-health

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