A new study suggests that a receptor protein called ERBB4 could be the missing piece in understanding how Alzheimer’s disease leads to memory loss. While previous research has linked the disease to abnormal protein clumps called amyloid plaques and tau tangles, the exact process by which these changes lead to cognitive decline has remained unclear. These proteins are known to cause overactivity in brain cells, weaken connections between them, and trigger changes in supporting cells, but the link to memory loss was not fully understood. Researchers at the Institute of Basic Science in South Korea discovered that abnormal activation of the ERBB4 receptor in certain brain cells might trigger multiple problems associated with Alzheimer’s at once. In mice showing Alzheimer’s-like symptoms, supporting brain cells called astrocytes and microglia were found to remove healthy connections between nerve cells. These non-neuronal cells also disrupted the balance of signals that regulate brain activity. In a healthy brain, the ERBB4 receptor is mostly found in neurons that inhibit signals and help maintain normal brain function. However, in Alzheimer’s-affected brains, ERBB4 was found in excitatory neurons, which are responsible for driving brain activity. This shift suggests that Alzheimer’s may not just destroy neurons but also push them into an abnormal state where they contribute to the disease’s progression. The study found that targeting the ERBB4 receptor could alleviate several Alzheimer’s symptoms. Researchers used gene-editing technology to remove ERBB4 from excitatory neurons in the hippocampus, a brain region critical for memory formation. This intervention reduced overactive brain cells, calmed the reactions of supporting cells, reduced plaque buildup, and improved memory and spatial awareness in mice. When ERBB4 was activated in a small number of excitatory neurons in healthy mice, the animals showed signs of excessive brain activity and cognitive difficulties. The researchers also looked at brain tissue from nearly 450 people who had died from Alzheimer’s and found that ERBB4 was more active in the affected neurons. They concluded that abnormal ERBB4 activity in excitatory neurons might be an early cause of Alzheimer’s disease and could be a promising target for treating not only Alzheimer’s but other neurodegenerative conditions as well.