Protein role in Alzheimer's.
Scientists found that the protein, called cypin, triggers the branching of neurons in the brain's memory centre.
The growth of branches, or 'dendrites', is an important part of brain function and thought to increase when a person learns.
More branches mean more connections, which are believed to underpin memory.
Dr Bonnie Firestein, who led the study at Rutgers University in New Jersey, USA, said, 'The identification of cypin and understanding how it works in the brain is particularly exciting since it opens up new avenues for the treatment of serious neurological disorders.
'This paves the way to designing new drugs that could target this protein molecule.'
Cypin was already known to exist elsewhere in the body. But until now, no-one knew what it was doing in the brain.
Dr Firestein's team found that only neurons with many branches that looked 'fuzzy' under a microscope contained cypin.
Stimulating neurons in a laboratory dish produced an increase in cypin, which triggered dendrite growth.
When the gene that makes cypin was blocked, a corresponding decrease in branching was observed.
The scientists, whose research appears today in the journal Nature Neuroscience, focused on the hippocampus, the region of the brain which deals with emotions and memory.
Dr Firestein said, 'One end of a neuron looks like a tree and, in the hippocampus, cypin controls the growth of its branches.
'An increase in the number of branches provides additional sites where a neuron can receive information that it can pass along, enhancing communication.'
The researchers found that cypin appeared to cement together the building blocks making the dendrite skeleton.
When cypin on its own was mixed with the building-block protein in a test tube, it caused the skeletal structures to grow.