Il dolore nel pensiero di Mario Tiengo
Review "Premio Tiengo 2022"
Pathos 2022; 29, 1. Online 2022, May 19
Stephanie Montani, Virna Terraneo
Università dell'Insubria, Varese
Professor Mario Tiengo devoted his whole life to scientific research on pain. It is to him that we owe the “Metaphor of Alice's mirror”, a metaphorical representation of how mental events can interfere with the phenomenon of pain. This work retraces Tiengo's ideas and his research on the relationship between brain and mind in the perception of pain
Il professor Mario Tiengo dedicò tutta la sua vita alla ricerca scientifica sul dolore. A lui si deve, oltre ad alcune tappe fondamentali della storia del dolore in Italia, l'elaborazione della “Metafora dello specchio di Alice”, rappresentazione di come gli eventi mentali possano interferire col fenomeno dolore. Questa review ripercorre il pensiero di Tiengo e le sue ricerche sul rapporto tra cervello e mente nella percezione dolorosa.
Pain, psychogenic pain, Alice's mirror
Dolore, dolore psicogeno, specchio di Alice
An anesthesiologist, Professor Mario Tiengo was the first to have a chair in Pathophysiology and Pain Therapy. He is responsible for the first university hospital centre for pain therapy in Italy, which was named after him and is currently part of the Policlinico of Milan.
His research on the relationship between brain and mind in the perception of pain is of crucial importance in the context of pain management at international level: in order to metaphorically represent how mental events can interfere with the phenomenon of pain, Tiengo conceived the “Metaphor of Alice's mirror”.1
This scenario also includes his interest in pain control within the obstetric field, as Director of the centre of obstetric analgesia at Mangiagalli Clinic. As a matter of fact, he was one the first to recognise the key role of the cognitive-emotional system on the control of childbirth pain, and to understand how the possibility of pharmacological intervention derives from the modulation of this system.
A distinction must be made between nociception and pain. Nociception is the set of neurophysiological and neurochemical events that occur from the nociceptors to the thalamic nuclei and that constitute the system of algic perception. By the term pain, however, we mean the effect that the sensory event has on consciousness, that is, the integration of the nociceptive message in the sensory, cognitive and affective areas of the brain.
Tiengo proposes a personal interpretation of the concept of pain, considering it as the realisation of nociceptive information: this would make a clear distinction between transmission of the nociceptive message to the brain and cognitive and emotional integration, from which the experience of pain emerges.2
Reception takes place in the periphery, at the level of a nerve ending whose function is to recognise harmful stimuli that affect the tissues of our body. The excitation of nociceptors and the consequent genesis and transmission of nociceptive information along the nerve fibres, up to the thalamic structures, results in painful perception only through a process of cognitive-emotional integration at the cortical level.
The pain perception mechanism is modulated by the antinociception system, i.e. the set of neural networks and neurotransmitter systems responsible for the control of pain. This is probably the most complex event of the pain phenomenon and occurs at different levels of the neuraxis: the posterior horn of the spinal cord, the bulb-mesencephalon, the reticular substance, the thalamus, the cerebral cortex. In numerous works Tiengo lays emphasis on how this system of endogenous analgesia cannot be reduced down to spinal modulation alone, whose main model is the “gate-control theory” by Melzack and Wall, but it rather involves several levels.3 Tiengo himself analysed how many bulbo-mesencephalic nuclei such as the reticular substance and the periaqueductal gray substance (PAG) are able to send further inhibitory impulses to the spinothalamic neuron, thus making it resistant.
According to Tiengo, the system of endogenous analgesia represents one of the most fascinating fields of study in pain management, as many molecules of analgesic drugs have a strengthening effect on this system.4
After focusing on the mechanisms of modulation of nociception, the next subject of interest in Tiengo’s studies was the perception of pain and its control. From these studies, it emerged that the modulation of the perception of pain occurs by modulation of the state of consciousness: if the neuronal system of consciousness is made resistant pharmacologically, for example with anesthetic drugs, or with non-pharmacological interventions such as hypnosis, conditioning, distraction techniques, the manifestation of consciousness does not occur, or occurs in a fragmentary way; this results in a lack or altered perception of stimuli. As for pain, the integration of thalamic nociceptive information in the circuits of consciousness evokes the perception of pain, in its two cognitive and emotional functional elements. It follows that mental events can affect the algic system and its control.5
The studies by Predrag Petrovich, a neuroscientist in Stockholm, and his collaborator Martin Ingvar, often cited by Tiengo, have helped to give an anatomical-physiological confirmation to this theory, demonstrating through radiological investigations conducted with magnetic resonance imaging the existence of functional connections between the endogenous analgesia system (PAG) and the limbic system, known to be responsible for emotional and affective control. There is therefore a dual mechanism by which emotional states can modulate pain, affecting both the phase of perception and that of transmission.
In order to clarify how mental factors can modulate the perception of pain, during his opening lecture on the occasion of the symposium “Highlight on Pain and Suffering” in Lugano in 1988, Tiengo proposed the metaphor of Alice's mirror, in which the mirror simulates the emotional and cognitive factors that carry out a modulation of perception, either increasing or decreasing it.6 The reflected image may appear to be different in size compared to the actual image. This depends on the degree of curvature of the reflective surface: the image will appear smaller if the mirror is convex, enlarged if it is concave. In this metaphor, the actual object is nociception, while the reflected image is pain. Continuing with the metaphor, the factors that determine the degree of curvature of the mirror are represented by all those psycho-emotional factors that influence the level of consciousness and painful perception. It follows that pain is represented by the nociceptive image reflected in the mirror, which can be real or distorted. Just think of those factors that can reduce the perception of pain to zero, such as suggestion, emotions, or mood.7 Or, on the contrary, think of the perception of pain that arises and persists, even without nociceptive stimulation.
The metaphor of Alice's mirror is mainly applied to the fields of psychogenic pain and childbirth pain, the two themes that were most studied and examined in depth by Tiengo throughout his long career.
The phenomenon of labour pains has very peculiar characteristics: it arises in a perfectly healthy individual, it is limited in time and immediately followed by the gratification associated to the birth of a child. From a pathophysiological point of view, it simultaneously features the three elements of pain: visceral, referred and somatic pain.8 However, there is also an «affective» element to childbirth pain: a complex reaction in which several factors are involved, including maternal age, physical and mental condition, culture, religious beliefs. The importance of the influence of these factors was demonstrated by Tiengo when he tried, with poor results, to use the “on-demand” inhalation of nitrous oxide in Italy, an analgesic technique which, however, was carried out successfully on Swedish women in labour.
In numerous studies, Tiengo, retracing Prof. Elsa Margaria’s ideas, focuses on the changes that occur during pregnancy and especially during childbirth. The main changes are hormonal and psychological: with respect to the hormonal structure, there is an increase in the blood levels of cortisol, progesterone and endorphins which leads to a raising of the pain threshold.9
From a psychological point of view, the nine months of pregnancy allow the person to adapt to ambivalent feelings: on the one hand, the conscious desire for motherhood and the desire to give continuity to one's mortal existence, on the other hand, the awareness of having to give up stable structures of one's own life to rebuild new ones. All of this is reflected in the moment of active labour, in which two processes of adaptation to painful uterine contractions can be distinguished: on the one hand, the biochemical modulation of the central and peripheral nervous system and on the other the emotional response of the woman to the painful stimulus. This response is influenced by an anxious state that in specific cases borders on the pathological: this seems to be the result of an excessive fear of pain during childbirth, dreading a possible unhappy ending for one’s self or for the baby. False beliefs, misinformation and socio-cultural legacies of the past contribute to these fears.
Two different emotional responses to childbirth pain can be therefore outlined: the first response is to fully embrace the natural process of birth, accepting the painful part as well, since it is thought that suffering is an integral part of childbirth. On the other hand, the second response is based on the principle that a true humanisation of birth cannot get along with pain and suffering. This translates into a request for help that must be accepted and carefully assessed in order to implement therapeutic measures accordingly. In several works, Tiengo emphasises how this therapeutic management cannot be limited to a pharmacological approach alone, despite it being often unavoidable, but must be integrated with techniques, such as suggestion, distraction and positive conditioning stimuli, that modulate the psycho-emotional aspects of the woman's past experiences and raise the pain threshold.10
Pain has a sensory part linked to receptor sensitivity and to its cortical processing, and an emotional part linked to multiple factors that modify the way pain itself is experienced and manifested. Tiengo emphasises that in clinical practice it is important not to focus exclusively on the “symptom of pain”, but also to analyse its expressiveness, that is, how the patient tends to experience and “represent” his/her pain. This phenomenon sometimes looks like a psychiatric disorder but lacks the data for a diagnosis. In 1980, and for the first time, psychiatric nosography included psychogenic pain in the category of somatoform disorders, characterised by an intense and persistent pain associated with the substantiated etiological role of psychological factors and with the absence of an organic pathology responsible for the pain or, in the case of an organic pathology, by a pain of such intensity as not to be congruent with the severity of the objective findings.11 However, this definition presents some issues for a number of reasons. First, it is difficult to objectify pain and then determine if it is more or less intense than you would expect. Second, the inability to identify pain-related physical conditions may be due to the fact that pain occurs before the organic damage is clinically evident; or else, the clinical evaluation may be be affected by previous therapies or operations. For this reason, with the DSM IV, the definition was revised and psychogenic pain was categorised as algic pain. Algic disorder is the presence in one or more anatomical districts of a pain not fully explained by a non-psychiatric medical condition and which presents a plausible causal relationship with psychological factors. Pain is indeed associated with an emotional discomfort that causes alterations in the social and work functioning.12 In support of this view, Tiengo observed that the treatment of this type of pain with analgesic drugs is not always decisive: in fact, it can lead to abuse and addiction. This observation can also be extended to the category of anxiolytics. Conversely, good results were obtained with the use of psychopharmaceuticals, especially with tricyclic antidepressants. A possible explanation for their efficacy is that patients with chronic pain may also have depression.
Depression is certainly the most common psychiatric diagnosis among patients suffering from pain: in some cases it is the cause, in others the consequence. The connection between pain and psychiatric syndromes has a long history in literature: Mongini, De Benedittis, Zanus are just some of the authors who dealt with this issue, paying particular attention to the relationship between pain and personality alterations.13 It has been observed that patients with such disorders (phobic, neurotic, anxious, depressive disorder) showed a lowering of the pain threshold and therefore a predisposition to algic pathology. An example of pathology that best illustrates the interaction between the algic sphere and the psychiatric sphere is fibromyalgia. It is a disorder characterised by the concurrent presence of widespread pain and hyperalgesia, associated with sleep and emotional disorders, in particular with anxiety-depressive manifestations. Some authors agree that pain and affective disorders in fibromyalgia share the same objective substratum and therefore their manifestation is concurrent. This hypothesis is based on a pathophysiological foundation: patients with fibromyalgia have indeed an altered metabolism of some neurotransmitters, and among them mainly serotonin. The latter, apart from its role in the genesis of anxiety and depression, is also involved in some processes of transmission and modulation of pain, especially at the level of the spinal cord, where its deficiency translates into a defect of inhibition of nociception. However, in subjects with fibromyalgia, emotional disorders are not always a constant element, as opposed to pain; for this reason, there are those who believe that anxiety and depression are reactive manifestations to chronic pain.14
This debate is still open: according to Tiengo, the problem is part of a broader discussion in which questions must be analysed through a teamwork between neuroscience and philosophy. In his paper “Patologia psichiatrica e dolore” (“Psychiatric pathology and pain”), Tiengo wonders how objective and subjective approaches to pain can best complement each other, and whether pain is really just a private experience that cannot be objectified.15
Tiengo’s works highlight that the transition from nociception to pain involves not only neurophysiological and neurochemical factors but also elements of the neurophilosophical and psychological sphere (such as anxiety, fear, panic, distraction, stress). The brain-mind binomial and its expression in algological terms is one of the fields of study that were most dear to him; when dealing with this field, he often mentions his collaboration with philosopher Karl Popper, who advanced the hypothesis that brain and mind were not the same thing but two distinct entities, although inextricably linked.16 The first supporter of this dualistic theory was John Eccles, Nobel Prize in Medicine in 1963 for his fundamental discoveries on brain synapses, with whom Tiengo had an important collaboration on the neurophysiology of pain. Eccles' proposal of the theory of psychons,17 according to which psychons interact with the neurons of the cortex through fields of quantum probability modulating their synaptic exocytosis, was not pursued. However, as specified by Tiengo, it is of crucial importance because it is the first attempt at providing a quantum interpretation of the mental modulation of pain perception. If the paradigms of classical Newtonian physics can be applied to nociception, pain, as well as all the scientific research on mind, consciousness and self, requires a different interpretation: the key is quantum physics. Tiengo writes: “The perception of pain can therefore be explored more deeply with the elusive world of quanta, conclusively recognising the failure of any attempt to reconcile clinical evidence and experimental data with common sense.”18
Despite understanding the importance and crucial role that these psychoemotional and cognitive mechanisms have in clinical practice, Tiengo is also aware of how much there is still to know about the endogenous mechanisms of analgesia connected to the limbic and cortical system.
Referring to the metaphor of Alice crossing the mirror, he writes: “It is like talking about Alice before and after crossing the mirror. It is the transition from a world that is familiar to us, logical, (a world) where we live every day, to an unknown world that contradicts and overturns all our cultural logic.” In recent years, the science of pain management has found an increasingly important and recognised space in the field of neuroscience. Every day, the appeal of neuroscience research opens up new horizons of understanding, ranging from the finest mechanisms of neuronal communication to neurophysiology and neuroimaging of mental processes, and therefore of pain. Among the topics of interest that form the background of this research, chronic pain stands out. Many authors do actually agree in asserting the superior efficacy of a multidisciplinary treatment, since at the origin of chronic pain a multifactorial mechanism can be identified, with a combination of bio-psycho-social, biographical, neurobiological, genetic and cognitive factors.19
Conflitto di interessi
Le autrici dichiarano che l'articolo è stato elaborato in assenza di conflitto di interessi.
30th May 2022
1) Tiengo M. Il dolore e la mente. Springer, Milano, Heildelberg, 2000.
2) Tiengo M. La percezione del dolore e il suo controllo: quello che ancora non sappiamo. Pathos 2008, 15.
3) Tiengo M, Scibilia G. Neurofisiologia del dolore. Anestesia e rianimazione 1975; 16: 83: 110.
4) Tiengo M. Il sistema dell’antinocicezione. In: Report dal XVII Congresso Nazionale AISD, 1994. Controllo del dolore: attualità terapeutiche. Pathos 1994.
5) Tiengo M. Dolore, riduzionismo e olismo. Pathos 2007, 14.
6) Tiengo M. Pain therapy can get rid of the spectre of euthanasia. Minerva Anestesiol 2001; 67:671-3.
7) Torta R, Lacerenza M. Depressione e dolore. Utet, Torino, 2002.
8) Margaria E. Historical war against the labour pain. Editoriale. Algos 1991; 8 (4): 7.
9) Di Leonardo C, Faldati M, Pezzani I, Sprignolo F, Petrovec MM, Rabasso A, Gasparini M, Nadbath P, Dogareschi T, Petraglia F (1999). Il controllo fisiologico del dolore nel parto. Atti del congresso: La nascita alle soglie del 2000: dove, come, quando.
10) Margaria E, Grea G, Castelletti I. Le componenti psicologiche del dolore da parto. In M.A Tiengo (ed): Il dolore e la mente. Springer-Verlag, Milano, 2000.
11) Scarone S, Gambini O. Disturbi da dolore psicogeno: aspetti clinici e terapeutici. In M.A Tiengo (ed): Il dolore e la mente. Springer-Verlag, Milano, 2000.
12) American Psychiatric Association (APA) (1994). Diagnostic and statistical manual of mental disorders (4th ed.) (DSM-IV), Washington DC: American Psychiatric Association.
13) Tiengo M, Mongini F (1999) il dolore e la mente: dolore somatoforme e dolore psichiatrico. In Tiengo M (ed) Il dolore: una sfida nella neuroscienza e nella clinica. Spinger-Velag, Milano.
14) Affaitati G, Vecchiet J, Giamberardino M.A, Vecchieti L. Ansia e depressione nella fibromialgia. In M.A Tiengo (ed): Il dolore e la mente. Springer-Verlag, Milano, 2000.
15) Tiengo M, Patologia psichiatrica e dolore, Volume 14 Pathos Nro 1, 2007.
16) Popper K, Eccles J. L’io e il suo cervello. Armando Editore, Roma 1996.
17) Tiengo M. Talking with Sir John, intervista a John Eccles sulla teoria degli psiconi. In: Seminari sul dolore. Mattioli Editore, Fidenza, 1992: 2:31-36.
18) Tiengo M. L’interpretazione quantistica della mente. In: Seminari sul dolore. Mattioli Editore, Fidenza, 1992: 2:27-30.