PLACING THE OPTODES The advantage of spring-loaded grommets over the standard ones is reduced setup time. With spring-loaded grommets you may place and secure sources and detectors in the corresponding grommets well before the experiment, without involving the subject. 1. Before proceeding to place sources and detectors into the corresponding grommets, make sure to have everything needed: a. The NIRScap (of appropriate size for your subject) which you have previously populated with springloaded grommet bases; b. Cable organizers. The number of cable organizers needed depends on the number of sources and detectors of the chosen montage. Each organizer can hold up to eight fiber optic cables and eight wires for active sources or detectors. The central slots are dedicated to the thicker optic fibers, and the lateral narrow ones are dedicated to the thinner wires of the active sources or detectors. Cable organizers are always provided in the Starter Kit. In this example, we will need two. a. Standard grommets. You will need one standard grommet for each cable organizer; b. Spring-loaded grommet caps; c. Sources and detectors of your NIRx system. 2. Place the cable organizers in the cap. One standard grommet is needed for every cable organizer. The organizers facilitate the routing of fibers and wires and relieve mechanical strain. They should be strategically positioned on the cap, based on the planned spatial arrangement of the probes. In this example, we will place both organizers in the occipital region, further away from the region of interest. Secure the standard grommets in the cap, and simply insert the cable organizers into the grommets. 3. Place the first optode into the corresponding grommet. If the grommets and their labels have been placed as illustrated previously, it should be straightforward to identify the correct grommet for each source and detector. Secure the optode by placing the spring-loaded grommet cap. You will need to slightly squeeze the bottom of the cap to make it fit into the base, to which it will ‘snap’. In this example, we will start with source “1”. 4. Once the optode is secured, make sure it is placed correctly: the optode tip should be protruding on the inner side of the cap. If the optode is placed correctly, you should be able to compress the spring by pushing the optode tip inside. 5. Once the optode is secured, push its cable or optical fiber into an available slit in the cable organizer. The central slots are dedicated to optical fibers, the narrow outer slots are dedicated to cables of active LEDs. While placing the cables/fibers in the organizer, make sure the wire or fiber is not pulling on the optode. When using a cable organizer for the first time, you may encounter some mechanical resistance when fitting the cable.