**7. Is optogenetics the future of noninvasive brain stimulation?**

Optogenetic techniques, where light-activated ion channels from microbial opsins are expressed in neurons enabling their activity to be controlled remotely by light, are rapidly increasing our understanding of neural circuits [95, 96]. In animal models, the technique has been used to investigate pain processing pathways; for instance, optogenetic activation of the prefrontal cortex has been found to lead to antinociceptive effects. This study highlighted the importance of a previously unexplored prefrontal to nucleus accumbens pathway that may in the future provide insights into treatment interventions for intractable pain [97]. As the field expands, optogenetic techniques are likely to lead to substantial increases in our understanding of pain processing by their use in animal models. In addition to the contribution to basic science, optogenetics has been predicted to have translational potential as a therapeutic neuromodulatory intervention for neurological disorders. One of the current limitations of the use of this technology in humans will be in how to safely deliver the channelrhodopsin (ChR2) gene to the targeted neuronal population. Nonetheless, it is likely that progress will occur very rapidly in this field due to its vast therapeutic potential [98].

**Conflict of interest**

**Author details**

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