How many neurons are in a mouse brain? - briefly
A typical laboratory mouse contains approximately 71 million neurons in its brain. Counts can vary modestly with strain, age, and experimental conditions.
How many neurons are in a mouse brain? - in detail
The mouse brain contains approximately 71 million neurons, a figure derived from multiple quantitative studies. This estimate represents the total neuronal population across all regions, including the cerebral cortex, hippocampus, cerebellum, basal ganglia, thalamus, and brainstem.
Key methodological points:
- Isotropic fractionator: tissue is homogenized, nuclei are stained with a neuronal marker (e.g., NeuN), and the proportion of neuronal versus non‑neuronal nuclei is counted. This approach yields a whole‑brain neuronal count with a reported margin of error of ±5 %.
- Stereology: systematic random sampling of histological sections combined with optical disector probes provides region‑specific neuron numbers. Summation across regions aligns closely with isotropic fractionator results.
- Strain variability: common laboratory strains (C57BL/6J, BALB/c) display counts ranging from 68 million to 74 million neurons, reflecting genetic and developmental differences.
- Sex and age effects: adult male mice typically exhibit slightly higher neuronal totals than females; neuronal loss becomes measurable after 18 months, reducing counts by roughly 10 % in aged specimens.
Regional distribution (approximate values for an adult C57BL/6J mouse):
- Cerebral cortex: 20 million neurons
- Hippocampus: 3 million neurons
- Cerebellum: 30 million neurons
- Basal ganglia and thalamus: 10 million neurons
- Brainstem and other nuclei: 8 million neurons
These numbers provide a comprehensive baseline for comparative neurobiology, modeling of neural circuits, and scaling of experimental data from rodents to larger mammals.