«October 2009 SCIENTIFIC COORDINATOR Pierre Le Neindre, Senior research scientist, INRA (French National Institute for Agricultural Research) ...»
Emotions result from cognitive processes which lead to the assessment of the characteristics of the stimulus encountered in the context of its occurrence. It appears that what is called "somatic markers of emotion” reflects in fact a sensory and cognitive analysis, usually performed automatically first, and then involving different levels of the central nervous system that are activated in parallel.
Sensory awareness Consciousness as a psychological phenomenon has rarely been addressed in studies on the neural mechanisms of pain. Research is focussed on aspects of emotional experience and the concept of consciousness is very rarely developed. In the present report, we restricted the definition of consciousness to the level of vigilance which corresponds to awareness from a neurophysiological point of view, and combines the perception of information from the environment and sensations from the body. In the neurological form of arousal, stimuli are transformed into sensory information, and noxious stimuli can be perceived as painful. This form of consciousness is always associated with, or triggered by, sensory information and corresponds with what is qualified as primary consciousness. Reflexive consciousness or self-consciousness does not lie within the scope of this assessment.
The functional dimension of consciousness (alertness and vigilance) has important practical implications, especially when animals are slaughtered for human consumption. It is the level of vigilance that allows or suppresses the emergence of a conscious sensation of pain resulting from the application of a noxious stimulus, such as bleeding at slaughter. Conversely, the lack of consciousness prevents higher structures of the nervous system (mainly the neocortex and the thalamus) to transform sensory stimuli into a sensation. The animal is in a state of partial unresponsiveness characterized by specific patterns of electrophysiological brain activity which can be observed during sleeping, some types of unprovoked seizures (epilepsy) or deep coma.
Experimental data collected by neuroscientists come mainly from work on humans and some primate species.
Based on their work it can be proposed that emotions of sensory origin (primary emotion) involve the existence of a basic form of consciousness called phenomenal consciousness which is simply experience. In this view, emotions arise because of primary consciousness (this does not require self awareness) and an individual’s drive to react would rely on this type of consciousness. In the case of pain, the first response is to rapidly move away from the noxious stimulus, and then to develop behavioural and postural strategies that make healing possible.
The world-wide accepted definition of pain was initially designed for humans. The relevance of this definition was to state that pain necessarily implies an emotion, in the sense of a primary emotion for protection and survival, which according to some authors falls into the category of “basic” or homeostatic emotions. However, it is noteworthy that even if it was formulated for humans, this definition does not mention phenomenal consciousness and its related forms, such as an increased level of vigilance, which corresponds with being on the alert. Questions on phenomenal consciousness have only emerged in recent years.
30 Expertise scientifique collective "Douleurs animales"2.3.2. Related notions
Suffering The word “suffering” is frequently used as a synonym for pain which includes sorrow, grief, disorientation, fear, anxiety, distress and depression. The official definition of the IASP, essentially formulated for medical studies, states that suffering is an "emotional distress associated with events that threaten the biological or psychological integrity of the individual”.
Irrespective of this definition, formulated for humans by physicians and neurologists, some philosophers have tried to distinguish between pain and suffering. Their argument is based on two facts. The first is that suffering is often associated with severe and long-lasting pain which affect body image and mental integrity. The second fact is that suffering occurs commonly in the absence of pain of physical origin.
Stress Pain is very often associated with stress because of its aversive dimension. Stress is defined as a reaction to a situation threatening the adaptability of the subject and which results in the activation of two systems: (1) the hypothalamic-pituitary-adrenal (HPA) axis which releases glucocorticoid hormones (cortisol and corticosterone), and (2) the sympathetic nervous system with the adrenal medulla which releases adrenaline and noradrenaline.
Stress refers to a standard physiological response that is not specific to the stimulus provoking it. It covers a wide range of phenomena of physical (abrupt changes in the environment), immunological (pathogens) or psychological (threat) origin. The concept of stress refers to the uniqueness of the physiological response towards extremely diverse stressors. Whereas common usage of the term stress may confound the aggressing agents and the organism’s response to them, here stress is defined as the overall, non-specific responses of an organism to stressors. The brain structures involved in stress responses are localised in the brainstem and the hypothalamus.
Activation of these structures leads to a series of neural responses directed to the spine and the endocrine glands, the so-called stress response. Functional interrelations between the pain neural network and the autonomic nervous system are found at peripheral and central levels. The most obvious sign is the relationship between acute pain and increased heart rate, blood pressure and peripheral vasoconstriction (paleness). The biological function of these responses is to enable the body to adapt to the threatening situation with a complex set of reactions such as energy mobilization, cardiovascular regulation by the autonomic nervous system, anti-inflammatory properties of glucocorticoids and their effects on the central nervous system. It must be borne in mind however that, although pain causes stress, a stress response is not necessarily painful. Stress responses may therefore help to detect the nature of noxious stimuli, but are in no way characteristic of pain.
Health Health is defined by the World Health Organization (WHO) as "a state of complete physical, mental and social wellbeing, and not just the absence of disease or infirmity."
In the past, health was seen as the opposite state of disease. Addressing health issues meant fighting against diseases. With the WHO definition, prevention and care are no longer the only means for safeguarding health.
Laws, regulations and political guidelines on environmental issues and land management are now included. The health of the population has become a political responsibility (Ottawa Charter, 1986).
The various elements defining pain that are exposed in this assessment are described in Figure 4 along with related concepts that are not directly taken into account. The scope of the ESCo assessment is represented by the red dotted line.
2.4 Transposing the concept of pain from humans to animals Nociception and pain in animals (if characterized as such) is likely to have the same biological functions as in humans: protection of the individual. Nociception and pain are just as vital to animals as they are essential to humans. However, it may be that the mechanisms involved in animal species (including non-human primates) are not strictly identical to those found in humans. This raises the following question: are the characteristics of noxious sensory-emotional experience in animals similar to those in humans, partly identical or fundamentally different?
This question is frequently posed by ethologists who study cognitive and emotional states in animal species.
2.4.1 Pain in animals
Definition of pain in animals The definition of pain given by the IASP was formulated for humans and is not applicable to animals. Since animals are unable to communicate verbally, they cannot reveal the characteristics of their sensory experience to humans.
The original definition of pain was therefore modified in order to provide one that was more suited to animal abilities. Hence pain is defined as the awareness that an animal has of an aversive sensory and emotional experience associated with actual or potential tissue damage.
32 Expertise scientifique collective "Douleurs animales"
The definition applies to vertebrates only and specifies that a painful sensory experience must trigger:
- protective motor responses withdrawal of a limb,
- neurovegetative responses (increased heart rate, higher blood pressure, peripheral vasoconstriction, transitional change in breathing),
- learned avoidance responses (long-lasting avoidance of a conspecific, avoidance of a predator or a place associated with an aversive experience, behavioural changes: animal becoming fearful, decreased exploration of a novel place...).
This definition, which is widely accepted by the scientific community, includes the concepts of emotion and saliency. The inclusion of emotion emphasizes the fact that pain is an aversive and unpleasant sensation, which is considered as a primary emotion. Referring to saliency draws attention to the fact that the existence of a form of consciousness has become, under the influence of cognitive sciences, a key element in recognising mental states in animals. It refers to the functional dimension of consciousness as defined in section 2.3.1, also called phenomenal consciousness.
Many animal species have emotions Only behavioural and physiological responses can characterise emotions in animals. This approach is based on work from cognitive psychologists who state that emotions result from an assessment of the situation experienced.
The level of assessment varies according to the cognitive abilities of a species. The assessment process relies on:
i) the characteristics of the triggering stimulus (suddenness, novelty, pleasantness...), ii) the corresponding inconsistency between the triggering stimulus and the individual’s needs or expectations; iii) the possibilities for adaptation proffered by the environment. The overall assessment leads either to a positive or a negative emotion.
From this perspective, the study of the emotional repertoire of farmed species is aimed at linking the neurobiological process involved in evaluating a particular event with the behavioural and physiological responses.
A series of studies undertaken on mammals, mostly rodents, indicates that the anatomical and functional substrates involved in the emotional state triggered by physical pain and those involved in the distress responses displayed after disruption of strong social bonds (separation of mother and young, for example) are similar. The fact that a small dose of morphine reduces significantly the vocal activity of rat pups separated from their dams suggests that such distress response relies on neurochemical mechanisms and brain structures that are also involved in physical pain. It can be assumed that there is neural network regulating the expression of emotions and that it may be activated by physical as well as by psychological threats.
Identification of neural structures activated by noxious stimuli in humans has shown that the negative affective state associated with it involves several brain areas of the cortex which are phylogenetically old, as well as the cortical somatosensory area SII. In contrast, non noxious somatosensory stimuli activate preferentially the cortical somatosensory area SI which is considered phylogenetically more recent; this cortical area is found in all primates.
The distinction between these two kinds of stimuli (noxious vs. non noxious) shows that there are two functional somatosensory components and that they are controlled by distinct neural pathways. It has not been established yet if this distinction is found at different levels of the animal phylogeny with the same characteristics. This raises many questions about the nature of the sensations experienced by species that differ as widely as vertebrates and invertebrates.
The characteristics of pain are modulated by the social environment Modulation of nociceptive thresholds The study of emotions and cognitive abilities opens up new perspectives for a better understanding of the emotional state of animals when they face noxious events, especially in livestock farming. Because of its affective component, animal pain might be modulated by emotions like it is in humans. The influence of emotions on pain has been investigated in animals by taking into account the context in which noxious events take place. Inducing positive emotions on farms may help improve the quality of animal life, in particular by reducing the perception of Expertise scientifique collective "Douleurs animales" 33 pain as has been shown for humans. Beyond the emotions themselves, which are by definition short-lasting, it is also important to take into account the consequences of a persistent emotional state, commonly called mood or basal affective state, which results from the accumulation of emotional experiences on the perception of pain.