Astrocytes were named for their star-like shape and, for most of a century, dismissed as scaffolding. They were thought to hold neurons in place, supply nutrients and clean up waste, useful but uninteresting. New experiments have overturned that assumption. Astrocytes appear to tune neuronal activity directly, altering how circuits process information and, in doing so, shaping mental and emotional states.
The evidence comes from experiments in which researchers manipulate astrocyte signalling and watch what happens to behaviour. Small changes in calcium activity in these cells can shift the timing of neuronal firing, adjust the strength of connections and influence how animals respond to stress or reward. The cells are not simply reacting to neurons; they are participating in the computation.
The implications reach the models neuroscientists build. Wiring diagrams that include only neurons, including the ambitious connectomes now being produced, may capture the hardware while missing a crucial layer of control. Brain function, it seems, is a conversation between cell types rather than a monologue delivered by neurons.
