Brain Reward Region Controls Eating via Small Hotspot
Eating without being hungry: almost everyone knows the feeling. But which brain cells actually give permission to keep eating, even after you have had enough?
The medial nucleus accumbens shell (medNAcSh) is a structure deep in the brain that has long been linked to reward behaviour and food consumption. But how exactly this region works was not well understood. New research published in eLife maps the mechanism in detail.
The researchers found that a specific group of nerve cells in this region, known as D1-SPNs (dopamine 1 receptor-positive neurons), reduce their activity during the consumption of rewarding food. That reduction is necessary and sufficient to authorise continued eating, regardless of whether the body actually needs the food. Moreover, this effect turns out to be concentrated in a small sub-region: a rostral hotspot within the medNAcSh.
Hedonic eating and aging
Hedonic eating, eating for pleasure rather than need, is a risk factor for weight gain and the associated health problems. In older adults, an additional factor comes into play: the sensitivity of the reward system changes with age. Dopamine production declines, and the way reward signals are processed shifts. This can lead to both reduced appetite and reduced control over eating behaviour.
Knowing precisely which cells release the brake during rewarding food consumption allows for more targeted thinking about treatments for obesity or eating disorders. That also applies to older adults in whom the reward system functions less effectively.
A switch, not a dial
What is striking about the finding is that D1-SPNs act like a switch, not a gradual regulator. The reduction in activity appears to cross a binary threshold: you eat, or you do not. That makes the system potentially sensitive to small disruptions. A minor change in the activity of these cells may already determine whether someone keeps eating or stops.
Whether this mechanism works in humans exactly as it does in animal models requires further research. But the precise localisation of the hotspot gives researchers a concrete target for follow-up studies.
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