The limbic system is a key component of an individual’s psychology. Mood, personality and risk reward behaviour are all intimately related to limbic function. The amygdala plays a particularly important role in this regard. The “thought viruses” discussed by Butler and Moseley [1] highlight how the amygdala and hippocampus, in particular, interact to produce behaviours that may then increase the likelihood of musculoskeletal symptoms. These behaviours may become learned further influencing symptoms.
Mood can directly alter the pain experience. In a study of 65 patients, pain tolerance but not ratings was significantly affected by reading depressive, neutral or positive statements. With positive statements increasing pain tolerance and the converse true for negative statements [2]. This highlights just how important attitude is in hardiness in dealing with musculoskeletal symptoms. This may be heavily influence by personality type.
Personality plays an important part in how someone handles a musculoskeletal dysfunction. McFadden and Woitalla [3] report on a patient with four different personalities who reported different function and pain on visual analogue scale and McGill pain questionnaire in each personality. Personality type is associated with coping ability and is strongly associated with the severity of symptoms. For example patients with facial pain and headaches score higher on the Minnesota Multiphasic Personality Inventory, compared to patients with intracapsular temporomandibular joint disorders [4]. Type D or the “distressed personality”, is especially sensitive to musculoskeletal symptoms. Mils et al [5] compared the symptoms of cancer survivors with Type D personality with the remainder of 3080 subjects. 19% had Type D personality and they reported more back pain and osteoarthritis during the study. Similarly, in 5012 students aged 15-18, the 10.4% of boys and 14.6% of girls with Type D personality were twice as likely to have musculoskeletal pain, and five times more likely to have psychosomatic symptoms [6]. Furthermore in borderline personality disorder the key differences compared with controls on neuroimaging are found in the limbic system [7]. Specifically areas that control and regulate emotions show hypometabolism and limbic regions show hypermetabolism when activated. The amygdala in particular shows hypermetabolism in response to emotive images compared with controls.
The amygdala helps mediate the reciprocal relationship between chronic pain and negative affective states such as fear and anxiety. The amygdala has a known role in emotions and affective disorders, and it is now implicated in pain modulation and emotional responses to pain [8]. The lateral capsular division of the central nucleus of the amygdala is know as the nocciceptive amygdala, and appears to integrate internal and external environmental information with nocciceptive input. The amygdala can facilitate and inhibit pain at different levels of the pain neuraxis.
The “thought viruses” outlined by Butler and Moseley [1] highlight how the interactions between the hippocampus and amygdala can influence behviours that are associated with worse outcomes among chronic pain patients. Thoughts around the severity of symptoms and reducing activity to protect an area are all likely mediated at least partially through the limbic system. With memories of past advice and past experience retrieved from the hippocampus and the risk reward weighed up in the amygdala. These thoughts are known to be associated with withdrawing from normal activities and protecting painful areas of the body. This can lead to a lack of stress on connective tissues leading to atrophy, architectural disorganisation, fibrosis, adhesions and contractures. If inflammatory mediators are predominating then the tissue is more prone to fibrosis as opposed to atrophy [9]. Fibrosed and atrophied tissues are likely to lead to myofascial pain through differing mechanisms.
Taken a stage further, in some the pain experience will lead to receiving treatment or finding ways of managing the symptoms through altering posture. Others receive encouragement to rest and possibly watch television in bed. Over time this behaviour is positively reinforced through operant conditioning and pain and behaviour may become learned [10]. This can lead to sickness behaviours and again is further associated with poorer outcomes.
An individual’s psychology is an important factor influencing how people respond to musculoskeletal symptoms. A poor mood increases pain sensation. A type D personality is a significant consideration in patients with chronic pain, and is evidently associated with poor outcomes. The amygdala and hippocampus are integral to the circuitry that leads to “thought viruses” producing the protective behaviours linked with illness behaviour and worse symptomatology. These behaviours may become learned and reinforced leading to the downward spiral towards chronic pain.
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