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In these experiments, the BOLD signal reliably scales with reward prediction error, which is a computation, the difference between the reward expected and recei
by jonnycomputer 7y ago
In these experiments, the BOLD signal reliably scales with reward prediction error, which is a computation, the difference between the reward expected and received. In short, we fit reinforcement learning models to in-task behavior, then correlate parameters of that model to neuroimaging acquired during that behavior.
fMRI does have quite a few limitations; BOLD signal is believed to reflect the amount of work being done, loosely, speaking, but it is not a computational signal in of itself; for reinforcement learning models we'd like to measure dopamine itself. Two decades ago, the pioneering work of Peter Dayan and Read Montague established that dopamine neurons report a prediction error signal (see: http://static.vtc.vt.edu/media/documents/SchultzDayanMontague1997Science.pdf http://static.vtc.vt.edu/media/documents/SchultzDayanMontagu...), but recording of neurotransmitter release in humans is hard, and frankly, long thought impossible (given ethical constraints). However, recent work by Read Montague has done just that. See: https://www.pnas.org/content/113/1/200 https://www.pnas.org/content/113/1/200 Keep tuned.
- mattkrause 7y agoDo you have any insight into why it took so long to do this in hmans? Fast-scan cyclic voltammeter was done in animals ~15 years ago by Wightman's group.
- jonnycomputer 7y agoethics, mainly. unlike macaques (etc.) we don't just stick probes in people. however, Parkinson's and epilepsy patients are getting implants for deep brain stimulation; Montague's group is working with hospitals performing these procedures. https://psychcentral.com/news/2015/11/29/new-insights-into-dopamine-function-in-parkinsons-patients/95495.html https://psychcentral.com/news/2015/11/29/new-insights-into-d...
- mattkrause 7y agoI wasn't sure if there was some advance in voltammeter techniques, or if it just took forever to find a willing patient and convince ethics to green-light it. DBS has been FDA-approved since the late 1990s (and even longer under IRB/IND stuff), so there have been lots of opportunities to stick probes in humans' heads.
- jonnycomputer 7y agoThere actually is a technical advance here; I just don't know enough about it to discuss intelligently (sorry). I would reach out to the researchers involved if interested.