King oyster mushroom (Pleurotus eryngii) reduced inflammatory activity in brain immune cells, with mushroom extracts and compounds like ergothioneine lowering stress signals tied to brain aging and cognitive decline. One compound, N-acetyltryptamine, reduced NLRP3 activation at 50 µM, while ergothioneine also suppressed inflammation at 500 µM, helping calm overactive microglia linked to memory problems and neurodegenerative disease. The strongest mushroom extracts performed similarly to blueberry extract, a well-known brain-health benchmark.