Optogenetics and chemogenetics are the more recent and popular methods used to study this relationship. Both of these methods target specific brain circuits and cell population to influence cell activity. However, they use different procedures to accomplish this task. Optogenetics uses light-sensitive channels and pumps that are virally introduced into neurons. Cells' activity, having these channels, can then be manipulated by light. Chemogenetics, on the other hand, uses chemically engineered receptors and exogenous molecules specific for those receptors, to affect the activity of those cells. The engineered macromolecules used to design these receptors include nucleic acid hybrids, kinases, variety of metabolic enzymes, and G-protein coupled receptors such as DREADDs.
DREADDs are the most common G protein–coupled receptors used in chemogenetics. These receptors solely get activated by the drug of interest (inert molecule) and influence physiological and neural processes that take place within and outside of the central nervous system.
Chemogenetics has recently been favored over optogenetics, and it avoids some of the challenges of optogenetics. Chemogenetics does not require the expensive light equipment, and therefore, is more accessible. The resolution in optogenetics declines due to light scattering and illuminance declined levels as the distance between the subject and the light source increases. These factors, therefore, don’t allow for all cells to be affected by light and lead to a lower spatial resolution. Chemogenetics, however, does not require light usage and therefore can achieve a higher spatial resolution.