Neuroscientists at MIT’s Picower Institute reported how the brain encodes information during decision making to keep options distinct and to retain memories of both chosen and unchosen alternatives. The findings appear in iScience and highlight that coordinated ensembles of neurons generate electrical patterns that separate options during consideration and after a choice.
In the experiment two animals were trained to look at one of two screen targets, each presented sequentially with its reward value, and to fixate the higher‑value target. Researchers recorded hundreds of neurons in the lateral prefrontal cortex and applied “declassifier” algorithms to decode the activity.
Decoding revealed functional ensembles whose collective firing distinguished target direction and value. By visualizing these ensembles as planes (subspaces) in a 3‑D plot, the authors showed that before a decision the patterns grouped by presentation order: all “target 1” planes were parallel, all “target 2” planes were parallel, and the two sets were orthogonal, indicating separate representations.
After the decision, new ensembles emerged. Chosen targets, regardless of presentation order, formed parallel planes, while unchosen targets formed another parallel set orthogonal to the chosen set. This alignment allows downstream circuits to read out the chosen location with a single decoder, independent of the initial order.
A single neuron could belong to different ensembles across trials—selective for option 2 in one round and for option 1 in the next—demonstrating that ensembles are ad‑hoc assemblies of multifunctional neurons rather than fixed circuits. Miller’s other work suggests brain waves can rapidly orchestrate such recruitment.
Maintaining distinct memories of both selected and rejected options supports credit assignment for future learning, such as remembering that choosing target 2 in round 3 yielded a reward. The authors conclude that dynamic subspace reorganization underlies option maintenance and selection in economic decisions.
The study was funded by the U.S. Office of Naval Research, the U.S. Army Research Office, the Freedom Together Foundation, and the National Institutes of Health.
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