Optogenetics uses genetic and optical means to express and activate light-sensitive opsin proteins in order to control the activity of specific cells and circuits in the brain and beyond. This method allows for unprecedented versatility and applicability  in regards to targeting strategies, millisecond precision in temporal control, and integration with other commonly used neuroscience techniques. The ability to perform optogenetics in conjunction with cellular, molecular, physiological, behavioral, and imaging approaches along with it's ability to be used in systems ranging from cell culture to behavior in awake, freely behaving animals make this tool essential for advancing our knowledge on the causal mechanisms underlying normal and disease states. 

Chemogenetics uses genetic and chemical tools to control the activity of specific cells in the brain. The main approach used in chemogenetics is the use of DREADDs (Designer Receptors Exclusively Activated by Designer Drugs). First, DREADDs are virally or transgenically expressed to target them to specific subtypes of brain cells and/or brain regions. A compound called CNO (clozapine-N-oxide) that activates the DREADDs is then administered either systemically or intracranially to activate or inhibit the target cells.

In addition to controlling the activity of cells with actuators like opsins or DREADDs, there is great interest in gaining a readout of the activity of discrete populations of cells to better understand relationships between cellular and systems-wide communication and the expression of behaviors related to cognition, emotion, motion, and motivation. Fiber photometery uses optical and microscopy tools to allow for the visualization and measurement of the activity of targeted cell populations during behavior in real time and can be used with or without concurrent modulation of cellular activity by optogenetic or chemogenetic means.