Summary: Decades of Alzheimer’s research have centered on toxic proteins such as amyloid-beta and tau. A new study from UC Irvine highlights a different and influential factor: early dopamine dysfunction in the entorhinal cortex, a brain region essential for forming associative memories.
The research shows that dopamine levels in this critical “memory gateway” fall to less than one-fifth of normal in an Alzheimer’s mouse model, disrupting neurons’ ability to encode new experiences. Crucially, the team demonstrated that memory function could be restored with Levodopa, a drug already approved for Parkinson’s disease.
Key Facts
- Severe Dopamine Loss: Dopamine in the entorhinal cortex dropped by more than 80%, leaving neurons unable to respond properly to information and form associative memories.
- Memory Restoration: Both optogenetic stimulation of dopamine fibers and systemic Levodopa administration normalized neural activity and recovered memory performance in mice.
- Circuit-focused Strategy: Instead of only removing protein aggregates, this approach targets the neuronal circuits that remain damaged even after plaques and tangles are addressed.
- Clinical Potential: Because Levodopa is already widely used and clinically tested for Parkinson’s disease, these findings could accelerate trials that evaluate dopamine-based therapies for early Alzheimer’s memory loss.
Source: UC Irvine
Why do memories fade in Alzheimer’s disease, and can they be restored? Researchers at the University of California, Irvine, led by Kei Igarashi, report a compelling answer: early and specific dopamine dysfunction in the entorhinal cortex undermines the brain’s ability to form new associative memories.
The Study and Its Findings
Published in Nature Neuroscience, the study pinpoints the lateral entorhinal cortex (LEC) as a site where dopamine signaling fails at early stages of Alzheimer’s pathology. The entorhinal cortex is a primary input to the hippocampus and plays a central role in binding sensory cues into lasting memory traces. In an amyloid precursor protein knock-in mouse model, the team measured dramatic reductions in dopamine and observed that neurons in LEC layers 2 and 3 no longer encoded associative experiences.
To test causality, the researchers used optogenetics to reactivate dopamine inputs to the LEC. That targeted reactivation restored normal neural encoding and rescued associative learning behavior. Parallel experiments using Levodopa (L-DOPA) produced similar improvements: neuronal responses were normalized and behavioral memory measures improved. These converging methods strengthen the conclusion that dopamine loss in the entorhinal cortex is a driver of early memory deficits in this model.
Igarashi and colleagues emphasize that dopamine’s role is not limited to reward processing. In the entorhinal cortex, dopamine acts like a “save” signal that enables new experiences to be consolidated into memory. When dopamine signaling fails, the brain cannot properly register and store new associations, which may explain aspects of early cognitive decline in Alzheimer’s disease.
Why this matters
Most therapeutic strategies for Alzheimer’s have focused on clearing amyloid-beta or tau protein accumulations. While reducing these pathological proteins remains important, this study suggests an additional, complementary strategy: restore and repair the neural circuits needed to form memories. If dopamine dysfunction leaves circuits unable to encode experiences, removing plaques may not be sufficient to recover cognitive function unless circuit integrity is also restored.
Because Levodopa is an established, widely used medication with a known safety profile, repurposing or adapting dopamine-targeted treatments could offer a faster translational path than developing entirely new compounds. The authors call for clinical investigation of entorhinal dopamine signaling in human patients with early Alzheimer’s disease to determine whether similar mechanisms operate in people and whether dopamine-based interventions can slow or reverse early memory loss.
Research Team and Acknowledgments
The research team includes Tatsuki Nakagawa, Jiayun L. Xie, Kiwon Park, Kai Cao, Marjan Savadkohighodjanaki, Yutian J. Zhang, Heechul Jun, Ayana Ichii, Jason Y. Lee, Shogo Soma, Yasmeen K. Medhat, and Kei M. Igarashi from the UC Irvine Department of Anatomy & Neurobiology, with Takaomi C. Saido at RIKEN Center for Brain Science, Japan.
Funding: The work received support from multiple NIH R01 grants, BrightFocus Foundation and Alzheimer’s Association grants, Brain Research Foundation and other awards, as listed by the authors.
Key Questions Answered:
A: Beyond reward, dopamine acts as a modulatory signal that permits the brain’s memory circuits to encode and stabilize new experiences. In the entorhinal cortex, insufficient dopamine prevents proper “stamping” of associative information into longer-term memory.
A: This research suggests a promising avenue. In the mouse model, Levodopa restored neural activity and memory function. Because Levodopa is already clinically approved for Parkinson’s, it may be a candidate for controlled trials in early Alzheimer’s, though human studies are needed to confirm effectiveness and safety for this indication.
A: No. Protein aggregates still matter as drivers of disease pathology. However, this study highlights that even after protein pathology begins or is reduced, circuit-level dysfunction—such as dopamine loss in the entorhinal cortex—can prevent memory recovery. Effective treatments may need to combine protein-targeting and circuit-repair strategies.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full.
- Additional context was added by editorial staff.
About this Alzheimer’s disease research news
Author: Carly Murphy
Source: UC Irvine
Contact: Carly Murphy, UC Irvine
Image: Image credit: Neuroscience News
Original Research: Open access. “Early dopamine disruption in the entorhinal cortex of a knock-in model of Alzheimer’s disease” by Tatsuki Nakagawa et al., Nature Neuroscience. DOI: 10.1038/s41593-026-02260-w
Abstract (condensed)
The entorhinal cortex, critical for memory formation, displays early histological and functional changes in Alzheimer’s disease. This study demonstrates that dopamine neurons projecting to the lateral entorhinal cortex become dysfunctional at early pathological stages, producing associative memory impairments in an amyloid precursor protein knock-in mouse model. Optogenetic reactivation of LEC dopamine fibers rescued associative learning, and L-DOPA treatment restored LEC neuronal memory encoding and behavioral associative memory. These results support the idea that early dysfunction of LEC-projecting dopamine neurons contributes to cognitive decline in Alzheimer’s disease and warrant clinical investigation of entorhinal dopamine in patients.