  Biological networks exhibit complex, coordinated patterns of activity. Can
these patterns be captured precisely in simple models? Here we use measurements
of simultaneous activity in 1000+ neurons in the mouse brain to test the
validity of models grounded in statistical physics. When cells are dense
samples from a small region, we find extremely detailed quantitative agreement
between theory and experiment; sparse samples from larger regions lead to model
failures. These results show we can aspire to more than qualitative agreement
between simplifying theoretical ideas and the detailed behavior of a complex
biological system.
