Consciousness can be applied to the senses or feelings, it is to feel love, cold, savor your favorite dish or suffer the loss of a loved one.
Consciousness is any possible experience. It is feeling love, cold, savoring your favorite dish or suffering the loss of a loved one. The word feel can be linked to the senses or feelings. However, when we refer to consciousness, the subjective experience or conscious experience occurs when we feel anything, regardless of its nature. If someone has been under the effects of general anesthesia, they know what the total absence of consciousness is. Through the use of these anesthetics, consciousness is lost, as well as in the deep phase of non-REM sleep or when we pass out from a blow to the head.
When we talk about consciousness we can make a conceptual distinction between states of consciousness and the content of consciousness. The state of consciousness with which we are most familiar is wakefulness, in which we experience the world. Whereas in non-REM sleep, another state of consciousness, we experience nothing. However, when we enter the REM phase of sleep, we enter a new state of consciousness where we have experiences in the form of dreams. Other states of consciousness are coma, where there is thought to be no consciousness, persistent vegetative state (PVS), where some patients are conscious and others are not, or lock-in syndrome or pseudocoma, where patients are completely paralyzed but fully aware.
Qualia, the content of our experiences
The content of consciousness is what philosophers call qualia. The smell of a rose, fear and sexual pleasure are very different experiences, that is, they differ in their content. Subjective experience or consciousness does not occur in the liver, kidney, or heart, but in the brain. However, not all the neurons that make up the brain contribute to consciousness. For example, if the cerebellum, which contains 69 billion of the brain’s 86 billion neurons, is removed, we remain conscious. From this it follows that not all parts of the brain contribute equally to consciousness.
The lesions in some structures that appeared very early evolutionarily are accompanied by alterations in the state of consciousness. For example, lesions in some areas of the brainstem (in the area of the neck) produce coma or PVE (persistent vegetative state). For this reason, it is believed that structures such as the brainstem generate the necessary conditions for consciousness to exist, that is, they are responsible for the states of consciousness.
On the other hand, the content of consciousness is produced mainly in the evolutionarily latest structure, which is exclusive to mammals and is highly developed in cetaceans, primates and in humans in particular: the neocortex.
If a very specific part of the neocortex is stimulated, patients report some specific type of conscious experience. For example, after stimulation of a part of the somatosensory cortex, patients feel that something touches an area of their arm. More complex experiences are also achieved, such as the evocation of specific memories or the urgent need to move a limb.
On the other hand, lesions in specific regions of the neocortex cause the loss of a specific type of conscious experience. Namely, lesions in specific regions can cause prosopagnosia (the inability to recognize faces), achromatopsia (color blindness) or akinetopsia (motion blindness). In these cases, the brain processes sensory information correctly, just as it would in people without this condition. In fact, in these patients the processing of sensory information affects behavior and decision making. However, this information processing is completely unconscious. In this way we know that there are some groups of neurons specifically in charge of generating the conscious experience.
What animals are Sentient
The states of consciousness would be produced by evolutionarily early brain structures such as the brainstem, while the conscious content would be produced by the neocortex, exclusive to mammals, in association with other structures such as the thalamus. So are all animals sentient?
To answer this question without misunderstandings, it is necessary to specify the difference between consciousness and self-consciousness. Self-awareness is a type of conscious or subjective experience that consists of introspection, of feeling that I exist as an agent separate from the environment that surrounds me. Self-awareness is a complex and particular type of conscious experience, which is especially developed in humans and is probably only possessed by a handful of animal species, such as some dolphins, cetaceans and primates.
The young child who plays a prank and does not know why he has done it has not yet developed insight or self-awareness.
However, even in humans self-awareness is not constant. In fact, it is believed that the neural connections responsible for self-awareness begin to mature around the age of 18 and end by the third decade of life. When a young child does some mischief and we ask him angrily why he did it, we should not be surprised by the answer “I don’t know”, since the introspective capacity or self-awareness is not developed. Likewise, even as adults, when we are focused on some task or absorbed in a movie or a book, we are not self-aware.
It is very common to confuse the terms consciousness and self-consciousness, hence the misinterpretation when we extrapolate it to animals. Using techniques such as binocular rivalry (presenting different images to each eye) some animals can be trained to tell researchers when they are aware of a stimulus and when they are not. Therefore, it is shown that some animals, such as macaques, are conscious. If these are, there is no reason not to grant the ability to experience the world to other mammals, since the brain they share is very similar. Although certainly, both quantitatively and qualitatively, the conscious experience will be very heterogeneous among mammals.
The problem comes when we apply the same intuition to other beings, such as octopuses, bees or magpies. The nervous system of these beings is different from that of mammals, which makes comparison difficult. However, they are complex nervous systems accompanied by behaviors that can be described as intelligent. This and other questions point to the need for a theory of consciousness that can explain its nature and predict which physical system, be it our cerebellum, the brain of an iguana, or a computer, experiences the world around it.
Brecht, KF and Nieder, A. (2020) ‘Parting self from others: Individual and self-recognition in birds’, Neuroscience and Biobehavioral Reviews. Elsevier, 116(June), p. 99–108. doi: https://doi.org/10.1016/j.neubiorev.2020.06.012.
Casarotto, S. et al. (2016) ‘Stratification of unresponsive patients by an independently validated index of brain complexity’, Annals of Neurology, 80(5), pp. 718–729. doi: https://doi.org/10.1002/ana.24779.