Abstract: Astrocytes are not only the most populous cell type in the human brain, but they also have the most extensive and diverse sets of connections, across synapses, axons, blood vessels, as well as having their own internal network. Unsurprisingly, they are associated with many brain functions; from the synaptic transmission to energy metabolism and fluid homeostasis, and from cerebral blood flow and blood-brain barrier maintenance to neuroprotection, memory, immune defenses and detoxification, sleep, and early development. And yet, notwithstanding these key roles, so many current therapeutic approaches to a range of brain disorders have largely neglected their potential involvement. In this review, we consider the role of astrocytes in three brain therapies; two are emerging treatments (photobiomodulation and ultrasound), while the other is well-established (deep brain stimulation). In essence, we explore the issue of whether external sources, such as light, sound, or electricity, can influence the function of astrocytes, as they do neurons. We find that, when taken all together, each of these external sources can influence many, if not, all of the functions associated with astrocytes. These include influencing neuronal activity, prompting neuroprotection, reducing inflammation (astrogliosis) and potentially increasing cerebral blood flow and stimulating the glymphatic system. We suggest that astrocytes, just like neurons, can respond positively to each of these external applications and that their activation could each impart many beneficial outcomes on brain function; they are likely to be key players underpinning the mechanisms behind many therapeutic strategies. 

Key words: deep brain stimulation, high frequency, infrared, mitochondria, red, ultrasound