Understanding the Sentient Mind

The mind, as such, does not actually exist. It is a complex abstraction that we can never fully grasp. The brain exists, which makes it easier for scientists to look into it using expensive bits of kit. We can observe the brain and its operation in ever increasing detail and record the electrical and chemical transmission of information. We can link specific sites and operations in the brain with specific thoughts and actions and provoke these actions with externally or internally applied stimuli. We know a lot about the biochemistry of emotion and the interactions between emotion and cognition: ways in which how we feel can affect the way we think. All this is fascinating stuff and vital to our understanding of the diagnosis and treatment of mental disorders but, so far, it falls a long way short of creating a coherent explanation of what we imagine to be the mind.

The question ‘What is mind?’ has engaged, employed and escaped the grasp of philosophers and scientists for more than 2000 years. Most of us adopt a more relaxed approach encapsulated by the exquisite phrase ‘be philosophical, try not to think about it’. We take it for granted that mind is a useful word to describe how we each interpret the world the way we see it. We might call this our mental state, but this is, once again, a circular argument. The majority position today, shared by philosophers and scientists is for physicalism, the assertion that mind is not an abstraction: everything in the mind is physical. Reductive physicalists assert that all mental states will eventually be explained in terms of measurable neurophysiological processes. This approach has obvious appeal to computer scientists developing better brains (and minds?) through artificial intelligence (AI). I am more sympathetic to the non‐reductive physicalists who argue that while all of the mind may be in the brain somewhere, it will never be possible to provide a complete (or even useful) description of the mind entirely in terms of neurobiology. We shall always need both the psychological and the common sense, every day, approaches to our understanding of mind if we are to make any practical sense of it at all.

My wish is to understand the sentient mind, especially in non‐human animals. I illustrate my approach with a simplistic but neurobiologically acceptable model of how a sentient animal interprets stimuli and sensations and what motivates it to respond (Figure 2.2). The control centre of the animal (the brain) is constantly being fed with information from the external and internal environment (outside and inside the body). Much information, e.g. our perception of how we stand and move in space, is processed at a subconscious level. In Figure 2.2, these actions are controlled by stimuli that pass directly from receptors in the central nervous system (brain and spinal cord) via the motor nerves to the muscles that control posture and movement. Having learned to walk, we are able to control our limbs without recourse to thought or emotion. Many animals, e.g. raptor birds and top cricketers, have an exquisite ability to process the movement of an object in flight and programme their own movements so as to catch it. This is an amazing property of the neuromuscular system, but the only ‘conscious’ element was the decision to go for the bird/ball in the first place.

The decision to act (or not) in response to a stimulus must involve some degree of interpretation. The brain of all sentient animals is equipped at birth with a foundation programme for survival constructed from the specific gene‐coded information acquired by its ancestors through generations of adaptation to the challenges of the environment in which they evolved. I refer to this property of mind as their mental birthright. For animals that demonstrate only the property of sensation, this may define the limits of their sentience. For animals that demonstrate the three inner circles of deep sentience, this foundation programme is expanded and enriched over time as a result of learning and experience. In animals with the power of perception, an incoming stimulus does not enter an empty room but becomes just another guest at the party, one that may or may not make an impact. In Figure 2.2, signals from external sensors such as the skin, the eye, the ear and internal sensors of, for example, biochemical parameters such as blood sugar, are recognised by the primary receptors as sensations (70). Much of this information from external sensors such as the skin and the eye will invoke a subconscious, reflex response like immediate withdrawal from a source of pain or threat. However. signals interpreted by the primary receptors as sensations will also pass to a second set of neural receptors linked to emotion (how it feels) and cognition (how it thinks). Negative stimuli like pain and hunger will be interpreted in the emotion centre as bad feelings and motivate the animal to conscious action to remove the source of pain or seek food. Other information, such as location or time of day may be interpreted simply as information with no emotional component and pass directly to the cognition centre. The response of the brain to incoming sensations and information may or may not involve a cognitive element but the motivation to conscious (as distinct from reflex) behaviour will nearly always have an emotional component. Indeed, I would argue that this is the essence of sentience.

To illustrate this concept, consider the primitive but clearly conscious sensation of hunger. The appetite control centre, which can be accurately located in the brain, will monitor internal stimuli such as low blood glucose or incoming sensory information from hunger pangs arising in the gut. It will also respond to natural external stimuli, such as the arrival of food, or a conditioning stimulus, such as the bell that Pavlov rang to condition dogs to anticipate the arrival of food. This direct information, like all incoming stimuli, will be interpreted in the context of existing food files in the brain carrying information from past experience as to the palatability, or possible poisonous nature of the food, or, if no food is currently on offer, the likely time to the next meal. If the animal is hungry and no food is available, it will experience a negative emotion that may range from slight to severe depending on how hungry it feels. When food arrives, it will feel good to a degree depending on the intensity of its former negative state (how hungry it felt) and the appeal of the food on offer. If the animal is already full up, it may treat the arrival of another meal with indifference: the information will be interpreted as neutral. My cats are masters of this studied indifference.

The notion that complex incoming information can be categorised on an emotional basis simply as positive, negative and neutral may seem overly naïve, but it is supported by classic experiments in neurobiology (33). Direct recordings from nerves in the brains of sheep reveal that when they are presented with food, or even pictures that indicate food (e.g. sacks of grain, bales of hay) these trigger signals in neurones that convey a positive message (a good feeling). Other images, e.g. pictures of dogs or humans, trigger a negative message (danger). However, when the sheep were shown an image of a familiar human carrying a bucket of food, these two categories of information (food and potential predator) were processed at the emotional level and passed on as a simple, unconfused positive message, ‘I feel good’.

Animals may need only the first two circles of sentience to experience hunger as a sensation that increases in severity the longer they go without food, and so increases the strength of motivation to seek a meal. Animals that possess the third category of sentience, namely perception, can adjust their actions in the light of their past experience, choosing, for example, high energy foods that they associate with greater satisfaction in the past and avoiding foods that they remember made them feel sick after the meal. I shall have more to say about this when considering the special skills developed by different species to meet their special needs. The message at this stage is that an animal with the faculty of perception can remember the nature and intensity of sensations that induce positive and negative emotional states and will be motivated to actions designed to make it feel better at the time and avoid circumstances likely to make it feel bad in the future. At this level, sentience can truly be described as ‘feelings that matter’.

In Figure 2.2, I have located the cognition and emotion centres on the left and right sides of the brain (we are looking at it from the front). Although this is overly naïve in an anatomical sense, it is consistent with current understanding of lateralisation within the conscious reception and control centres in the brains of vertebrates (61). In mammals, the cerebral cortex is divided into two distinct halves, with some linkage via the corpus callosum. Nearly all sensory and motor nerves cross over before entering and after leaving the brain so that the left side receives sensation from and controls muscles in the right side of the body and vice versa. So far, straightforward. The really interesting feature of lateralisation is that the left and right sides of the brain interpret incoming information and sensation in different ways. In humans, the left side of the brain appears to be primarily involved in the processing of information in detail, the right side with getting an overall feeling about the big picture. Humans with damage to the left brain have an impaired ability to understand and use language. Malfunctions in the right brain are associated with disorders of emotion: depression and delusions. All this reinforces the notion that the sentient mind possesses the properties of both emotion and cognition. Sometimes, it operates on the basis of feelings and thought, but always on the basis of feelings. This concept was central to the thinking of the psychiatrist Iain McGilchrist who entitled his investigation of the divided brain ‘The Master and his Emissary’ (50), the master being the right, emotional side holding the big picture, the left being the well‐trained civil servant with the learning and skills needed to do the right thing. I should add that Plato was there first with his allegory of the mind as a charioteer driving two horses, passion and logic.

The relevance of lateralisation to our understanding of the sentient mind in non‐human animals is beautifully illustrated by the behaviour of birds, who have no corpus callosum so minimal links between the left and right brain. Vision, sensory input from the eyes, like nearly all other sensory information, crosses over en route to the brain. Thus, information from the right eye is processed in the left brain and vice versa. When chickens are foraging for food, seeking information, they tend to favour their right eye, so transmit specific information to the left side of the brain where it is interpreted in detail. When on the look‐out for, or under threat from a predator, they favour the left eye, so stimulate a broad emotional response, fear, fight or flight (62).

To summarise the argument so far: the sentient mind operates primarily on the basis of feelings, modified to a varying degree by cognition, simply expressed as the ability to think about sensations and emotions. The power of cognition is widespread throughout the animal kingdom. We already know a lot about the cognitive abilities of mammals and birds and are discovering more and more evidence of the capacity of fish and invertebrates like cephalopods to construct complex mental formulations. I shall have much more to say about this. The point I wish to emphasise at this stage is that, for sentient animals, including humans, most of the time, cognition is acting in the service of emotion.

I make no claim that this is a novel insight. Two observations from David Hume, from his 1740 Treatise on Human Nature (230), are of note.:

Reason is, and ought only to be the slave of the passions, and can never pretend to be any other office than to serve and obey them.

The causes of these passions are likewise much the same in beasts as in us, making a just allowance for our superior knowledge and understanding.

Later philosophers (but not Darwin) have quarrelled with this bleak, animalistic view of nature. Humans may argue, without clear evidence, that we are better than this because we alone possess the fifth skandha, namely consciousness, the facility of being aware that we are aware. Clearly this has enabled some of us to plan and do clever things. However, we evolved as sentient creatures and the evidence strongly suggests that we too, most of the time, are motivated primarily by how we feel, whether our considered actions be selfish or altruistic. This is a good reason why I am confident that AI will never reproduce the human brain. For sure, it can make information processing computers that are better informed and quicker thinking than ours, so do amazing things such as creating better antibiotics, or playing better chess. However, I do not envisage an artificial brain driven by how it feels. Scientists will, I am sure, develop an artificial brain that appears to act according to how it feels but I suggest that this will be no more than a brain that acts according to how they feel it should feel, which is not the same thing.

Animals do not require the deepest circle of sentience, namely consciousness, in order to interpret and remember past experiences and the feelings they arouse. They cannot be said to live only in the present. Their emotional state will be defined by their expectations of the future in the light of past experience. This has profound implications for our understanding of the impact not only of primitive emotions such as pain and fear but also so‐called ‘higher’ feelings such as hope and despair, comfort and joy.

Pain and Suffering

Pain in humans has been described as ‘an unpleasant sensory and emotional experience associated with actual tissue damage’. This is a good definition insofar as it recognises both the elements of sensation and emotion. Too many physiologists in the past have ducked questions concerning the emotional elements of pain, preferring simply to consider nociception, the sensation of pain. Some have argued that pain, even in humans, is such a subjective experience that it is not open to scientific explanation. To answer them, I again recruit Wittgenstein ‘just try, in a real sense, to doubt someone else’s fear and pain’ (85). I am happy to extend that doubt to other sentient species. In what follows, I shall adopt the simple model illustrated by Figure 2.2 and describe sensations and emotions associated with pain simply as positive or negative, in full recognition of the fact that these bald terms lack subtlety of meaning. I shall use ‘mood’ when I refer to emotional responses. Many scientists prefer the word ‘affect’. I can think of no good reason why.

The possession of a sentient mind brings with it the capacity to suffer. This feeling may be modified by cognition. For example, the mood of a woman with severe abdominal pain will differ according to whether she knows she has cancer or is giving birth to a baby, but the sensation may be the same. We can say with some certainty that potential sources of suffering in non‐human animals include pain, fear, hunger and thirst, severe heat and cold, malaise (feeling ill) and exhaustion. We can say with equal certainty that we humans can suffer from anxiety and depression, boredom and frustration, loneliness and loss. We have a duty to explore the extent to which we may share these ‘higher’ emotions with other sentient species.

We can describe our own experience of pain as a negative experience, a bad thing, both in terms of the immediate sensation and its emotional consequences. We seek to avoid sources of pain, we take drugs to reduce the sensation and, if the pain persists, our mood takes a turn for the worse. In recent years, there have been many excellent, compassionate studies of pain as a sensory and emotional experience with mammals, birds and fish that convince me of their capacity to suffer. My personal links with this largely involve the work of colleagues at the University of Bristol with broiler chickens (34,39). I shall briefly summarise this work as an illustration of a more general theme.

The word ‘broiler’ describes chickens that are selectively bred and reared to produce meat as quickly and cheaply as possible. Modern broiler strains can progress from the moment of hatching to the moment of slaughter in 40 days or less. As a result of this, extreme pressure for increased productivity of an increasing number of birds has developed what the trade has called, without shame, ‘leg weakness’. As they approach slaughter weight the birds become increasingly reluctant to move, many go off their legs altogether and die or have to be culled, not least because they can no longer reach the feeders. The pathology that gives rise to leg weakness is complex. It can involve both abnormal bone growth and joint damage, often exacerbated by infection, but it is all precipitated by the fact that these birds are outgrowing their strength. There are serious issues of animal welfare and human ethics arising from the problem of leg weakness in broilers. These have been addressed at length elsewhere and it is fair to say that the industry, largely in response to consumer pressure, has gone some way to putting its house in order. However, this is outside my current brief, which is strictly concerned with the extent to which the pain associated with this condition of leg weakness strains of this bird that have been selected for rapid growth may be a source of pain and suffering.