Chronic pain is one of the common health problems among the general population. Various mechanisms are involved in the pathophysiology of pain, and a correct understanding of its pathophysiology or cause is important for an optimal management of pain. In terms of the physiological anatomy, pain with physical ⁄ organic causes can be classified mainly as “nociceptive pain” or “neuropathic pain.” However, there is also pain that does not fall into either of these two categories. This type of pain is often considered as a third classification, but its definition has not been standardized globally. In Japan, this type of pain is often called “psychogenic pain,” even when the pain is not attributed to psychological factors. However, it may not be an appropriate term for this particular type of pain. Firstly, because there is no standardized definition, physicians differ in how they classify pain as “psychogenic.” Additionally, the term “psychogenic” could give negative impressions to patients, which can deteriorate the patient–physician relationship and may result in poor treatment outcomes. In this paper, we have discussed these problems and proposed a new term “cognitively perceived pain” for this third category of pain, with the aim to foster a more appropriate, and easy–to–understand classification of pain. “Cognitively perceived pain” encompasses all pain that is neither nociceptive nor neuropathic pain, including that described as centralized pain or sensory hypersensitivity, in addition to psychogenic pain according to its original meaning (i.e. pain attributable to psychological factors). Because pain is perceived in the brain, the presence of any pain implies the impairment or abnormality of cognition. The proposed term is straightforward to convey the essence of pain without including any negative–sounding words. We hope that this term and its concept will be widely accepted, and help to increase understanding of this poorly defined category of pain.

There is growing evidence that fatty acids function as signal transduction molecules in a variety of biological phenomena with improved technology and precision of fatty acids analysis. For example, recent study have revealed that the functional properties of fatty acids are modulated by the amount of individual fatty acid intake, identification of the fatty acid receptors and the changes of its expression, and the distribution of fatty acids among organs.

Now, the relationship between polyunsaturated fatty acids and pain is getting a lot of attention as one of the modulation factor of pain. n–3 fatty acids alleviate pain caused by inflammation and neuropathy, whereas blood levels of n–6 fatty acids are increased in patients with chronic pain and thus exacerbate pain. Furthermore, we have proposed fatty acid receptors may function as a potential target molecule in pain. On the basis of these reports, it is likely that fatty acids play a major role in the regulation of pain.

In this review, we discuss current status and our recent study regarding fatty acids as novel pain management molecules.

It has been accepted the fact that patients with chronic pain comorbid with depression or anxiety appeal profoundly severe pain condition more than healthful emotional condition. The critical treatment of chronic pain has not been appeared although noradrenergic and serotonergic neurons were discovered as a target of treatment such as depression or anxiety. Recently, the importance of function of the n–3 free fatty acids (FFAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid is focused on the novel target of chronic pain. However, the mechanism has not been elucidated. The G–protein coupled receptor 40 ⁄ free fatty acid receptor 1 (GPR40 ⁄ FFAR1), a receptor of middle–long chain FFAs including DHA, distribute in the brain of human and rodents. We previously reported that the GPR40 ⁄ FFAR1 suppressed not only various pain stimuli via activation of endogenous pain regulation systems but also depression–like behavior. Our previous study demonstrated that the GPR40 ⁄ FFAR1 knock–out mice show the persistent of mecha­nical allodynia after hind–paw incision. Furthermore, the GPR40 ⁄ FFAR1 knock–out mice show the abnormal emotional behaviors. Our results suggested that the GPR40 ⁄ FFAR1 has the potential of the novel therapeutic target of stress–induced chronic pain.

There are many reports the surgery results and depression of the lumbar spinal stenosis (LSS), and preoperative evaluation of depression is regarded as important. However, not only depression but other psychological problems such as anxiety and fear may be involved in dysfunction of LSS patients.

The subjects were 346 patients (211 males, 135 females) of LSS preoperation from September 2010 to March 2016, and the age was 68.8 ± 9.8 years (mean ± SD). The patient–reported outcomes of LSS uses Roland–Morris Disability Questionnaire (RDQ), Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ), Zurich Claudication Questionnaire (ZCQ), and psychological evaluation includes Self–Rating Questionnaire for Depression, The Pain Catastrophizing Scale, Pain Anxiety Symptoms Scale–20, Hospital Anxiety and Depression Scale, Brief Scale for Psychiatric Problems in Orthopaedic Patients. Spearman's rank correlation coefficient of various psychological evaluation and patient–reported outcomes was analyzed. In addition, according to the cut–off point of various psychological evaluation, it divided into the normal group and the ab­normal group, and the difference of severity of patient–reported outcomes was statistically compared and examined. There was no meaningful correlation between various psychological evaluations and patient–reported outcomes of LSS patients used this time (|r|<0.4).

In comparison with the normal group and the abnormal group of various psychological evaluations, there was a significant difference in RDQ, JOABPEQ lumbar spine dysfunction, social life, ZCQ pain in all psychological evaluation, dysfunction was severe in the abnormal group (P<0.05). It was found that various psychological factors are also related to the lumbar functional dysfunction considered to be an organic disability. Psychological disorders such as anxiety, depression, fear, etc. in addition to disability caused by LSS may exacerbate dysfunction of LSS patients.

We organized Yamaguchi Pain Center in Yamaguchi university hospital to treat chronic pain patients. We are performing multidisciplinary therapy and treating the patients in hospital for 3–4 weeks. In this study we examined whether there is a difference between elderly and young middle–age suffering from chronic pain. As a result, young middle–aged people were more painful than older people. And Eldelry people did not see psychological improvement of pain. At present it is difficult to change the psychological aspect the pain of elderly people during hospitalization. It is necessary to be able to receive support in the area after other hospital.

Emotional sweating is a physical reaction that occurs with pain and other acutely stressful situations. Very few studies have directly evaluated emotional sweating to monitor pain reception in full–term newborns. The aim of study was to examine whether emotional sweating could applicate for evaluating procedural pain by heel lance in full–term newborns. Eight full–term newborns participated on the fourth day after birth in this study. We examined whether the amount of sweat secretion changed during blood collection procedure. The sweating reaction was recorded continuously from the start of the blood collection until blood collection was finished, using the probe of a portable perspiration meter against the newborn’s palm. As a result, the amount of emotional sweat significantly increased in perspiration accompanied the heel lance, compared to the baseline before blood collection. These finding suggest that emotional sweating could be used as an objective index of procedural pain in full–term newborns.