How does pain affect behaviour?

Pain is defined as 'an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage'. Namely, pain may be experienced with or without physical damage to the body and is subjective and unique to every individual.

Although pain is the endpoint of nociceptive input, autonomic pathways and areas of the brain involved in emotion and memory are also implicated, so it becomes a multi-dimensional experience. There are many different types of pain, including neuropathic, somatic and visceral pain, which can then also be either acute or chronic depending on duration.

Physiological pain is essential for survival as it facilitates the identification of potentially harmful stimuli that can subsequently be avoided, and also allows for convalescence.

How does pain affect behaviour?

Animals are nonverbal and cannot self-report the presence of pain, therefore the burden of pain assumption, recognition, and assessment lies with veterinary professionals. It is now accepted that the most accurate method for evaluating pain in animals is not by physiological parameters but by observations of behaviour.

Obtaining a thorough patient history from the owner can help determine abnormal behaviour patterns that may be pain-related, and home video recordings of the concerning behaviour can be a useful aid to assessment.

Altered social interactions  

Whether physical or emotional, pain and/or the anticipation of pain can affect the emotional states of animals by causing stress, anxiety and fear. The anticipation of pain might therefore motivate avoidance or escape behaviours which, as well as retreating and hiding, could involve aggressive behaviour aimed at repelling any stimuli perceived as potentially painful.

Avoidance and aggressive behaviour might also communicate unwillingness to receive or engage in interaction or tactile manipulation (as discussed in aggressive behaviour). Pain might also play a part in separation-related/attention-seeking behaviour, as some dogs might solicit increased social inclusion and desire to be with their owner for greater security and support.

Altered posturing, movement and associated behaviour or willingness to engage in activity 

The experience of pain might manifest as altered movement, of the whole body or isolated parts. Lip-smacking or holding the body very still in a bowed stance might occur in response to gastrointestinal pain for example, or star-gazing in response to spinal or dental pain.

Although it can be very difficult to assess, lameness is another more obvious example. However, it is always worth being mindful that pain may be overridden by a dog’s desire to engage in various activities despite the pain experienced.

The possibility that a dog will overcompensate for pain experienced at a localised region of the body, such as a specific limb, and suffer discomfort/result in damage elsewhere within the body is another factor worth considering when assessing a dog for pain.

Altered normal daily routine 

Dogs experiencing or anticipating pain might prioritise resting over exercise or other activity, however, it is important to be aware of competing motivations in which the desire to perform a specific behaviour overrides the desire to avoid pain.

For example, a dog with dental disease could still eat, and a dog with arthritis may still want to chase a ball with the same vigour as displayed prior to any pain experienced. This phenomenon, coupled with individual degrees of stoicism, can complicate pain diagnoses.

Altered ability to concentrate and learn 

Pain can also negatively affect cognitive ability and interfere with the ability to concentrate and learn, as well as remember things. Pain might be experienced more intensely at night due to the lessening of other distractions, and has been shown to disrupt sleep in dogs, which also contributes to the negative impact of pain upon learning ability. Sleep deprivation also increases the perception of pain and can depress the mood.

Formation of new distraction behaviours 

A dog might also attempt to alleviate or cope with physical or emotional pain by performing specific distracting behaviours, for example, licking/nibbling an area of their body or tail-chasing, even if these areas are not the source of pain.

Initially associated with endorphin release, these behaviours make the dog feel better so might be performed repeatedly until they progress into habitual and compulsive behaviour.

This then becomes maladaptive for the individual, causing, for example, dermatitis, lick granulomas, or tail-tip trauma, which can continue long after the initial cause of the pain has been treated and resolved.

Noise sensitivity

Musculoskeletal pain has been positively linked with sensitivity to noise in dogs5. Fagundes, A., et al. 2018, hypothesise that this could be due to the sudden increase in muscle tension which can occur when a dog is startled by a loud noise. In a dog with a pre-existing musculoskeletal condition, this could exacerbate pain.

Negative associations

Another complication with the experience of pain is that an individual might associate it with other concurrent stimuli, which might then impact how they feel about this stimulus when next exposed to it. For example, a dog who runs accidentally into an electric fence and receives an electric shock while out walking in the company of young children might associate the painful experience with the children.

They might consequentially develop anxiety around children as an unfortunate outcome of this association. Another example might be a dog who has experienced dental or neck pain when eating becoming reluctant or worried about eating in general. In this way, painful associations may become generalised more widely.

It is worth planning an analgesia trial in combination with behaviour modification in any case where you suspect that the underlying cause of the behaviour change is due to pain. The choice of analgesic and whether one or more agents are required will vary between individuals and depend on factors such as type of pain, (such as musculoskeletal or neurological) as well as the underlying health of the patient, such as whether renal or hepatic compromise is present.

The duration of the analgesia trial should ideally be eight weeks. But six to seven at least to definitively rule out pain as an underlying factor of the behaviour change. Some dogs might also have learned to anticipate a painful response to behaving in a particular way.

In such cases it might be necessary to extend the trial beyond eight weeks, in order to allow time for the behaviour modification programme/training plan to be implemented and for the dog to learn a different way of behaving. This eventuality is worth considering at the start of every pain trial.