Here, we found that the fish analog of the mammalian astrocyte is a central computational element of a circuit implementing a behavioral-state change after integrating sensory information. Specifically, radial astrocytes in a subregion of the brainstem in larval zebrafish temporally integrate noradrenergically encoded failures to accumulate evidence of futility before inducing a state of passivity (giving up). This behavioral pattern has a familiar combination of features: trying to achieve a goal, repeatedly failing despite trying harder, giving up temporarily, and then trying again. Fish swim more vigorously in open loop (i.e., ineffective swim attempts), become passive, then swim again.First try harder, then give up for a while.
Using whole-brain imaging, we found that astrocytic calcium was elevated just before and during passive states. Activation and silencing experiments established that these glial cells are required to trigger the passive state. Neuronal imaging and manipulation showed that the NE system encodes an expectation-outcome mismatch signal, which activates Ca2+ signaling in radial astrocytes. Thus, behavioral failures are detected by NE-MO and integrated by glia, which, after accumulating sufficient evidence of motor futility, trigger a passive behavioral state via GABAergic neurons. Once passivity is triggered, its persistence may be due to sustained effects of the glial cells on neurons, or a lag in the reactivation of swim circuits.In other words, the astrocytes serve as a kind of scorecard or abacus outside of the neurons. The neurons click up the astrocytes, and when the number of raised beads reaches a threshold the neurons tell the muscles to stop swimming. = = = = = ** Later thought: It's obvious that frustration is universal, but why is it universal? Why do so many situations need this calculated give-up response? Specifically, why would zebrafish need to know when their attempt to swim didn't result in forward motion? Virtual reality experimental setups aren't exactly common in the real ocean. A headwind in the current would be the main reason for lack of progress. When you're moving against a headwind you do have to try harder, but I'd think the frustration response would include something like gliding down to the floor for stability until the current slows down, or turning around to swim with the current.
Labels: Grand Blueprint
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