Astrocytes: integrators of arousal state and sensory context

Abstract

The integration of external information with the internal state of the body is central to the survival of virtually every multicellular organism. However, a complete picture of the mechanisms that govern this process is lacking. In this opinion article, we synthesize evidence demonstrating that astrocytes sense the momentary arousal state - through neuromodulator release - as well as the sensory inputs - through local synaptic activity - and respond to them with changes in calcium (Ca²⁺) signaling. We hypothesize that astrocytes integrate sensory signals with the internal state and that this process is necessary to secure optimal behavior. Finally, we argue that dysfunctional astrocytic Ca²⁺ signaling could be an underlying factor in disorders characterized by disrupted sensory processing.

Keywords: calcium signaling; glial cells; internal state; neuromodulation; sensory processing.

Figure 1.. Astrocytic Ca²⁺ signaling as an integrator of external and internal information.

(A) Visualization of the proposed concept: astrocytes integrate sensory information, conveyed by synaptic activity in neuronal circuits, and arousal information, conveyed by neuromodulator release, by means of differential Ca²⁺ signaling. Salient sensory stimulation can increase arousal levels, and in turn, arousal-related neuromodulators affect sensory processing in neuronal circuits. While not discussed in detail here, the signaling events downstream of astrocytic Ca²⁺ that facilitate interactions with neuronal activity and modulate sensory experiences remain elusive (dotted arrow; see Outstanding questions). (B) Heat map illustrating the anticipated magnitude of astrocytic Ca²⁺ signaling due to the integration of arousal level and sensory input.