On the experiment diagram, distinct interventions nodes are used for different types of interventions: surgical intervention, pharmacological intervention, pathogen infection and euthanasia. For interventions which do not fit into any of the aforementioned categories, the node ‘other intervention’ can be used. For example the other intervention node can be used to represent an environmental stimulus in a behavioural assay, such as conditioning, scruffing or exposure to light. It can also be used to represent tissue processing steps, such as microscopy or immunohistochemistry.
Distinct intervention nodes have different properties fields; this enables the users to input information relevant to a specific type of intervention. Typically, an experiment contains multiple nodes of the same type, as treatment and control groups are subjected to variations of the same intervention. If the intervention defines the different categories of a variable of interest, then duplicates of the variable categories nodes should be used to tag the intervention nodes, as seen in the image below.
An experiment can contain multiple types of intervention. For example in Example 4, mice are subjected to a first intervention: they are placed in a cage with a running wheel, this is represented on the diagram with a node ‘other intervention’ and as the intervention is different in treatment (the running wheel rotates) and control animals (the running wheel is fixed) two distinct nodes are used. Then all animals are anesthetised and treatment and control animals go through the exact same procedure so this is represented by a single euthanasia node.
The properties of all intervention nodes include a description of the intervention and details about its timing, which refers for example to the time of the day at which the intervention was carried out, the time relative to the start of the experiment or to another intervention, or the length of time each intervention takes, if it is relevant. Any adverse effects expected should also be noted there. For example, the image below shows the properties of the pharmacological intervention node, accessible by clicking on the properties icon circled in red.
Information specific to the intervention type include:
- Pharmacological intervention – drug and dose, along with the mode of administration
- Surgical intervention – anaesthetic and analgesic regimen, duration of anaesthesia and anticipated success rate
- Pathogen infection – infectious agent and dose load
- Euthanasia – method used and tissues collected at autopsy