Scientists discovered that altering levels of the KCC2 protein can dramatically change how the brain forms reward associations.
Reduced KCC2 boosts dopamine activity, making new habits—good or bad—form more easily.
How a Brain Protein Shapes Learning and Habit Formation
New research from Georgetown University Medical Center shows that the brain’s ability to link cues with rewards can shift depending on the activity level of a specific protein. This process helps us decide when to respond to signals that lead to beneficial outcomes and when to ignore cues that reinforce harmful behaviors, such as those involved in smoking addiction.
“Our ability to link certain cues or stimuli with positive or rewarding experiences is a basic brain process, and it is disrupted in many conditions such as addiction, depression, and schizophrenia,” says Alexey Ostroumov, PhD, assistant professor in the Department of Pharmacology & Physiology at Georgetown University School of Medicine and senior author of the study. “For example, drug abuse can cause changes in the KCC2 protein that is crucial for normal learning. By interfering with this mechanism, addictive substances can hijack the learning process.”
The study, funded by the National Institutes of Health (NIH), was published today (December 9) in Nature Communications.
KCC2 Levels Influence Dopamine Firing and Reward Learning
The investigators found that shifts in learning can arise when levels of the KCC2 protein change. When KCC2 levels drop, dopamine neurons tend to fire more often. This increase in dopamine activity can promote the formation of new reward links. Dopamine neurons are specialized nerve cells responsible for producing and releasing dopamine, a neurotransmitter involved in reward, motivation, and movement.
To explore this process, the researchers examined rodent brain tissue and monitored how lab rats behaved during classic Pavlovian cue-reward tests. In these experiments, a brief sound signaled that a sugar cube was coming. In addition to tracking how changes in KCC2 affected the speed of neuron firing, the team discovered that synchronized bursts of activity among neurons could unexpectedly boost dopamine release. These short dopamine spikes appear to play an important role in how the brain assigns value to shared experiences and learns from them.
Why Certain Cues Trigger Strong Cravings
“Our findings help explain why powerful and unwanted associations form so easily, like when a smoker who always pairs morning coffee with a cigarette later finds that just drinking coffee triggers a strong craving to smoke,” notes Ostroumov. “Preventing even relatively benign drug-induced associations with situations or places, or restoring healthy learning mechanisms, can help develop better treatments for addiction and related disorders.”
How Diazepam and Other Drugs Influence Neuron Coordination
The researchers also wanted to determine whether drugs that act directly on cell receptors, including benzodiazepines such as diazepam, could affect learning. Earlier studies suggested that modifying KCC2 production can change neuron behavior and influence how diazepam (valium) produces its calming effects. The current findings shed light on an additional layer of neuronal function: neurons do not just adjust their firing rate, they can also coordinate their activity. When this coordination occurs, information moves through neural circuits more efficiently. The researchers found that drugs like diazepam can support this coordinated activity during testing.
A Multi-Method Approach and Why Rats Were Used
“To reach our conclusions, we combined many experimental approaches, including electrophysiology, pharmacology, fiber photometry, behavior, computational modeling, and molecular analyses,” says the study’s first author Joyce Woo, a PhD candidate in Ostroumov’s lab.
She added that the team chose rats for the behavioral portion of the research because rats typically perform more consistently than mice on extended or complex tasks. Their reliability in reward-learning experiments helped the investigators gather more stable data.
Broader Implications for Brain Disorders and Treatment Development
“We believe these discoveries extend beyond basic learning research,” says Ostroumov. “They reveal new ways the brain regulates communication between neurons. And because this communication can go wrong in different brain disorders, our hope is that by preempting these disruptions, or by fixing normal communication when it’s impaired, we can help develop better treatments for a wide range of brain disorders.”
Reference: “Dynamic changes in chloride homeostasis coordinate midbrain inhibitory network activity during reward learning” by Joyce Woo, Ajay Uprety, Daniel J. Reid, Irene Chang, Aelon Ketema Samuel, Helena de Carvalho Schuch, Caroline C. Swain and Alexey Ostroumov, 9 December 2025, Nature Communications.
DOI: 10.1038/s41467-025-66838-x
In addition to Ostroumov and Woo, authors at Georgetown include Ajay Uprety, Daniel Reid, Irene Chang, Aelon Ketema Samuel, Helena de Carvalho Schuch, and Caroline C Swain.
Ostroumov and his co-authors report having no personal financial interests related to the study.
This work was supported by NIH grants MH125996, DA048134, NS139517, DA061493, as well as grants from the Brain & Behavior Research Foundation, the Whitehall Foundation, and the Brain Research Foundation.
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1 Comment
“Reward” sounds very objective. ‘Need’ is a key.