Uncertain Expectations

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Science  10 Jun 2005:
Vol. 308, Issue 5728, pp. 1521
DOI: 10.1126/science.308.5728.1521a

Life is full of “what-ifs,” yet each of us has to collapse multiple uncertainties into a binary yes/no in order to be able to make any decisions at all. Yu and Dayan have constructed a computational model that combines two types of uncertainty—the first incorporates the predictive value of a validated cue, and the second quantifies the likelihood that the existing cue is no longer valid and that a new one needs to be identified—and propose that these are encoded by the neuromodulators acetylcholine (ACh) and norepinephrine (NE); to be precise, by cholinergic and noradrenergic circuits, respectively. In their generalized Posner task, a red arrow points toward the side where the target will appear most of the time, whereas arrows of other colors are randomly oriented. As the predictive value of the red arrow declines, acetylcholine increases. At unspecified times, the red arrow stops carrying information, and another arrow becomes the predictive cue. During this changeover, norepinephrine increases, signaling the need to search for the cuing color. When the exquisite balance of these systems is disrupted, inappropriate behaviors ensue: A drop in norepinephrine leads to perserverence and a lack of adaptability; conversely, a drop in acetylcholine results in hyperdistractability. — GJC

Neuron 46, 681 (2005).

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