Between Saturdays
This Week: how glial cells power the brain’s connective framework, why sleep acts as the brain’s cleansing cycle, and how microglia shape cognitive aging.
Neurons may get all the attention, but they make up only a fraction of the brain. Surrounding them is a vast, intelligent scaffolding — the glial network. These cells form the brain’s connective tissue: insulating, nourishing, repairing, and even shaping thought itself. This week’s four studies explore what keeps that hidden network healthy and how nutrition, sleep, and lifestyle sustain the brain’s resilience over time.
Caught My Eye…
Sleep: The Brain’s Cleaning Cycle
While we sleep, glial cells drive the glymphatic system, a specialized clearance network that flushes out metabolic waste, including amyloid-β and tau proteins.
A 2025 review in Nature Medicine synthesized recent imaging studies showing that deep non-REM sleep increases interstitial fluid flow by up to 60%, enhancing toxin clearance. Sleep deprivation, even for a few nights, disrupts glial water channel expression (AQP4), leading to waste buildup.
The review also noted that consistent sleep timing, not just duration, correlates with better glymphatic function. Regular bedtime routines may therefore protect the brain as effectively as diet or exercise.
Microglia, Inflammation, and Cognitive Aging
Microglia, the brain’s resident immune cells constantly scan their environment, pruning synapses and removing waste. But when chronically activated, they release inflammatory molecules that can damage neurons. A 2024 meta-analysis in Frontiers in Aging Neuroscience examined over 50 animal and human studies exploring microglial activation and aging. It found consistent associations between elevated inflammatory markers (IL-6, TNF-α) and reduced cognitive performance. Interestingly, interventions that improved microglial regulation such as omega-3 fatty acids, polyphenols (like resveratrol), and regular physical activity reduced neuroinflammation and improved learning and memory scores in older adults. The review concluded that microglia aren’t inherently harmful; they simply reflect the brain’s metabolic environment. When inflammation rises systemically, they respond in kind.
Astrocytes as the Brain’s Metabolic Architects
Astrocytes, long dismissed as mere “support” cells are now recognized as metabolic architects of the brain, orchestrating how energy and information flow through neural networks. A 2023 review in Frontiers in Neuroscience synthesized decades of findings showing that astrocytes not only assist neurons but actively manage their performance. They absorb glucose from blood vessels and convert it into lactate, providing neurons with rapid, efficient fuel during activity through the astrocyte–neuron lactate shuttle. They also regulate glutamate and GABA levels to stabilize neurotransmission, and synthesize essential lipids that sustain myelin repair linking dietary fats directly to cognitive resilience. Under chronic stress or inflammation, astrocytes shift into a reactive state, disrupting mitochondrial efficiency and promoting neurodegeneration. In essence, astrocytes serve as metabolic gatekeepers, translating diet, oxygen, and circulation into neuronal energy and signaling. When they falter, the brain’s stability, cognitive and metabolic alike all begins to unravel.
Rethinking the “90% Glia” Myth
For decades, it has been claimed that glial cells make up “about 90%” of the human brain and that larger brains contain proportionally more glia, but a 2014 review dismantles both ideas and offers a clearer framework for how glia and neurons actually scale. The analysis shows that glia do not form a fixed majority, their proportions vary widely by region and species and that the glia-to-neuron ratio does not increase uniformly with brain size or differ predictably between gray and white matter. Instead, the ratio depends on neuron size and density: regions with larger, more metabolically demanding neurons are supported by more glia per neuron, ensuring energy balance and homeostasis. This scaling rule appears consistent across mammalian evolution, suggesting a conserved design principle where glial abundance matches neuronal workload rather than brain volume. Far from being passive “glue,” glia actively regulate ion balance, energy delivery, and information processing scaling with the physiological needs of neurons. The takeaway is simple: glia don’t just fill space; they sustain the brain’s energetic framework. Supporting brain health, therefore, means supporting this glial infrastructure through nutrition, sleep, and inflammation control that keep neurons alive, efficient, and connected.