The mental state and demeanour of animals may be described as dull, depressed, unresponsive, unaware, sleepy, apprehensive, anxious, timid, bright, alert, aware, excitable, hypersensitive and aggressive. It is the animal's carer who is usually best able to make such assessments by their knowledge of the animal's normal behaviour under similar conditions. Systematic, validated methods for assessing depression in animals have not been found. The interaction of the animal with others of the same species or humans is important and may change during painful episodes (Pritchett et al 2003).
In humans, pain may affect their ability to learn tasks. In some animals it may be possible to appreciate changes in their ability to perform learned tasks, including responses to commands or in their ability to learn new tasks.
It is generally accepted that animals subjected to adequate anaesthesia for surgery do not feel pain. They may exhibit reflex responses but the forebrain should be so affected by the anaesthetic that it is unable to support any conscious experience and the animal should be unaware of any noxious stimulation.
Consciousness/awareness should be assessed by subjecting the animal(s) to visual or auditory threats or enticements (Pritchett et al 2003). Such tests need to include the use of memory and higher level cerebral function to register the threat and it is also essential that the animal has the motor competence to respond appropriately. Neuromuscular blocking agents abolish motor responses and should not be administered to conscious animals.