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> They are a very large  cell and modulate neurons:
> 
> https://mail.google.com/mail/u/0/#trash/FMfcgzQbfLWxPPwbTWKtfhGGxSvpHVKn
> 
> They discovered that, when calcium builds up in astrocytes, they release the energy-carrying "molecule ATP into the space between cells. Enzymes convert the ATP into adenosine, a known neuromodulator in the brain, which then activates neurons in the hindbrain and causes the fish to stop swimming.
> 
> “'It was surprising to me because it seems like such an indirect pathway,” lead study author Alex Chen says in a statement. “First of all, a non-neuronal cell is involved and then, second of all, there’s this biochemical circuit instead of some sort of neuronal circuit that implements this behavior.” This type of indirect circuit operates on a much slower time scale than neural circuits and could be useful for changes in behavior that occur over periods of seconds or minutes, the team speculates.
> 
> ***
> 
> "the new study describes experiments in mice that demonstrated that norepinephrine actually triggers a wave of coordinated activity in astrocytes, which use their calcium levels to regulate how the neuromodulator affects synapse activity. “ It seems that a lot of brain wiring and activity is probably orchestrated by astrocytes, on slower timescales,” senior study author Thomas Papouin explains in a statement. “This is the type of discovery that profoundly reshapes our understanding of how the brain works.”
> 
> "A third study examined astrocyte activity in the brains of live fruit flies and found that these cells play an active role in regulating complex neuronal signaling networks. Because astrocytes are quite large, they can receive signals from thousands of neuronal connections at once. But instead of becoming overwhelmed, these cells pick and choose which neurons to listen to by switching off their ability to respond to neurotransmitters like dopamine and glutamate. The team found a similar mechanism in rodent brains, suggesting that it evolved early and has continued to be relevant for survival. “ If a tiger is behind you, you need to rapidly change how whole brain regions are thinking,” lead study author Kevin Guttenplan explains in a statement. “It’s time to shut out everything else on your mind and entirely focus the brain on escaping.”
> 
> 
> "Together, these findings add to growing evidence that astrocytes play a much more active role in the brain than previously thought. The new studies should also change the way scientists think about “investigating neurological and psychiatric disorders that involve dysregulation of neuromodulation,” neuroscientist Cagla Eroglu writes in a related Science Perspective. She notes that disorders like depression, anxiety, and schizophrenia, which are traditionally attributed to neuronal dysfunction, “may stem from disrupted astrocyte signaling.'”
> 
> Comment: because the effect of astrocytes action is so indirect it was late in discovery. They were placed there for a reason and now that reason is now understood. From a design standpoint having systems for slower reactions makes perfect sense.