How global mental states affect consciousness – a neurobiologial perspective
Research on consciousness has made great progress, but basic knowledge of fundamental aspects of consciousness is lacking. Conscious experiences is the defining characteristic of “consciousness” and refers to the fact that it “feels like” something to see, hear, etc. A second aspect is the state of consciousness, which refers to the global mental state that forms a basis for consciousness.
It is commonly assumed that the state of consciousness specifically affects conscious experiences. This seems intuitive, as we loose our ability to have conscious experiences when we “loose consciousness”. However, people can have conscious experiences even though they are sedated, and we can process information unconsciously even when we are awake.
Could it be that the state of consciousness actually do not have a specific relation to conscious experiences, but rather is such a basic aspect of how the brain works that it affects all mental processes, irrespective of conscious experiences? This is currently debated, but empirical data is lacking.
Our unique contribution is to empirically investigate whether the global mental state do have a specific relation to conscious experiences. We will in a series of experiments examine how the state of consciousness affects mental processes by manipulating both the state and the conscious experience of sensory input, while brain activity is measured with fMRI. In doing so, we will spearhead current knowledge of what it means to “be conscious”.
Final report
Purpose and development
In research on how the brain generates consciousness it is common to either manipulate the level of consciousness or the content of consciousness. To experimentally manipulate the content, it is possible to use various stimulus-presentation techniques (e.g., “continuous flash suppression”) and compare how the brain processes information that the participant had an experience of seeing (i.e., had a conscious experience of) to information that the participant has processed without having an experience (i.e., unconscious processing). To manipulate the level of consciousness one can instead use medical substances that alter wakefulness and for example compare brain activity when a person is conscious with loss of consciousness. It has, however, remained unclear how these two aspects of consciousness are related. We have therefore in this project, for the first time, combined the two types of manipulations to clarify how brain activity changes as a function of both level of consciousness and conscious/unconscious information processing. A key question is if the level of consciousness specifically alters conscious information processing, or if it alters information processing regardless of what the participants are subjectively experiencing (i.e., both conscious and unconscious processing). Because the level of consciousness can be manipulated with several different substances and also vary naturally (sleep/wakefulness), and because the underlying mechanisms vary across substances, we aimed to manipulate the level of consciousness in several different ways to be able to investigate possible differences in how the level of consciousness alters conscious/unconscious information processing.
Implementation
The project consisted of three separate studies, where the manipulation of the content of consciousness were held constant across all experiments (visuospatial stimuli that were shown or hidden from conscious awareness by using “continuous flash suppression”) but where propofol, ketamine, and sleep deprivation was planned to be used to manipulate the level of consciousness. A crucial aspect of the experimental protocol was to not sedate the participants such that they lost consciousness, but only to reduce the level as much as possible without diminishing the participants ability to perform the behavioral tasks that were to be solved while their brain activity was measured using fMRI. A stable behavior is crucial to reliably determine which stimuli that participants consciously experienced and which were unconscious. Study 1 (propofol) went well, but during pilot testing for study 2 (ketamine) we found that the dissociative effect from ketamine made it difficult for the participants to follow instructions and perform tasks reliably. We therefore switched from ketamine to dexmedetomidine for study 2 – a switch that turned out to be very fruitful (see below). Study 3 (sleep deprivation) went well but was delayed and more difficult to perform due to the corona pandemic.
Important results and conclusions
In study 1 we found that propofol affects both conscious and unconscious information processing. The implications from this are that one cannot assume that a change in the level of consciousness only alters the brain processes that are associated with conscious experiences. Previous research that has aimed to investigate how the brain generates conscious experiences by manipulating the level of consciousness should therefore be interpreted with caution, because the differences that have been found may well be related to unconscious information processing. Consequently, we suggest that use of the term “level of consciousness” is often ill-advised and terms like “wakefulness”, “arousal” or similar is more appropriate.
In study 2 we found that dexmedetomidine specifically alters conscious information processing, while unconscious processing was not significantly changed. This opens for the possibility that continued research on the effects of dexmedetomidine could help clarify the neurobiological basis of consciousness in a unique way. Current research indicates that dexmedetomidine primarily alters the level of the neurotransmitter noradrenaline. Noradrenaline is associated with several brain processes, including attention and memory. Noradrenaline is considered to qualitatively alter how nerve cells process information, while other neurotransmitters, for example acetylcholine and GABA, “only” alter their amplitude. Possibly, these and similar puzzle pieces can result in increased understanding of how the brain generates our consciousness. However, several questions remain before we can say with certainty that noradrenaline specifically alters conscious information processing (see below).
The data collection for study 3 (sleep deprivation) was delayed as a consequence of the corona pandemic, but is complete and data analyses are in progress. There are, however, currently no results available.
New research questions
An important part of the science of consciousness is to try to understand which individuals have the capacity for conscious experiences. This is highly relevant for, e.g., patients with brain damage and to reliably know that patients that are sedated for major surgeries will not have to experience the surgical procedures. Several “markers of consciousness” have been suggested in the scientific literature, but the underlying research have not previously taken unconscious information processing into consideration. The results from study 1 demonstrates that this is problematic. Given the experimental paradigm that we here have developed (the combined manipulation of level and content of consciousness) it is now possible to verify previous markers, or to develop more reliable alternatives.
The finding that dexmedetomidine specifically alters conscious information processing provides promising opportunities, because it may provide information on the neurophysiological mechanisms of consciousness. There are, however, several questions that need to be sorted out before strong conclusions can be made. One of the problems are that noradrenaline is associated with selective attention. Possibly, the effects we have seen in our data are due to altered attention rather than reflecting a direct relation between the levels of noradrenaline and conscious information processing. A second problem is that different neurotransmitter systems in the brain interact with each other. Thus, altered levels of noradrenaline can lead to altered levels of acetylcholine, dopamine, etc. Continued progress therefore hinges on that the relation between noradrenaline and conscious information processing can be verified.
Since this is the first time that both the level and content of consciousness have been manipulated simultaneously, it is important that the findings are replicated, but also that the generalizability is investigated. For example, it remains unclear if the effects from altered arousal on conscious and unconscious processing is the same if other stimuli, tasks, and manipulations of the content of consciousness, are used.
Dissemination of research and results
Results from the project has been, and will continue to be, published with Open Access in international peer-review journals. They have also been presented at international scientific conferences and local scientific events, as well as in teaching. Participation in scientific conferences has been negatively affected by the ongoing corona pandemic.
List of publications
Papers:
Fontan, A., Lindgren, L., Pedale, T., Brorsson, C., Bergström, F., & Eriksson, J. (2021). A reduced level of consciousness affects non-conscious processes. NeuroImage. doi: 10.1016/j.neuroimage.2021.118571
Eriksson, J., Fontan, A., & Pedale, T. (2020). Make the unconscious explicit to boost the science of consciousness. Frontiers in Psychology, 11:260. doi: 10.3389/fpsyg.2020.00260
Fontan, A., Lindgren, L., Pedale, T., Brorsson, C., Karampela, O., Bergström, F., & Eriksson, J. (in preparation). Noradrenergic activity may be a valid target for pharmacological manipulations of consciousness.
Conference presentations:
Fontan A., Lindgren L., Pedale T., Bergström F., Brorsson C., Eriksson J. (2019) Changes in the global state of consciousness affect brain activity related to conscious and non-conscious visual experiences differently. Poster presented at the annual meeting of the Society for Neuroscience, Chicago, USA, October 19-23.
Karampela, O., Fontan A., Lindgren L., Pedale T., Bergström F., Brorsson C., Eriksson J. (2022) Sedation: A probe to explore the neural mechanisms of consciousness. Poster to be presented at the annual meeting of the Organization of Human Brain Mapping, Glasgow, Scotland, June 19-23.
In research on how the brain generates consciousness it is common to either manipulate the level of consciousness or the content of consciousness. To experimentally manipulate the content, it is possible to use various stimulus-presentation techniques (e.g., “continuous flash suppression”) and compare how the brain processes information that the participant had an experience of seeing (i.e., had a conscious experience of) to information that the participant has processed without having an experience (i.e., unconscious processing). To manipulate the level of consciousness one can instead use medical substances that alter wakefulness and for example compare brain activity when a person is conscious with loss of consciousness. It has, however, remained unclear how these two aspects of consciousness are related. We have therefore in this project, for the first time, combined the two types of manipulations to clarify how brain activity changes as a function of both level of consciousness and conscious/unconscious information processing. A key question is if the level of consciousness specifically alters conscious information processing, or if it alters information processing regardless of what the participants are subjectively experiencing (i.e., both conscious and unconscious processing). Because the level of consciousness can be manipulated with several different substances and also vary naturally (sleep/wakefulness), and because the underlying mechanisms vary across substances, we aimed to manipulate the level of consciousness in several different ways to be able to investigate possible differences in how the level of consciousness alters conscious/unconscious information processing.
Implementation
The project consisted of three separate studies, where the manipulation of the content of consciousness were held constant across all experiments (visuospatial stimuli that were shown or hidden from conscious awareness by using “continuous flash suppression”) but where propofol, ketamine, and sleep deprivation was planned to be used to manipulate the level of consciousness. A crucial aspect of the experimental protocol was to not sedate the participants such that they lost consciousness, but only to reduce the level as much as possible without diminishing the participants ability to perform the behavioral tasks that were to be solved while their brain activity was measured using fMRI. A stable behavior is crucial to reliably determine which stimuli that participants consciously experienced and which were unconscious. Study 1 (propofol) went well, but during pilot testing for study 2 (ketamine) we found that the dissociative effect from ketamine made it difficult for the participants to follow instructions and perform tasks reliably. We therefore switched from ketamine to dexmedetomidine for study 2 – a switch that turned out to be very fruitful (see below). Study 3 (sleep deprivation) went well but was delayed and more difficult to perform due to the corona pandemic.
Important results and conclusions
In study 1 we found that propofol affects both conscious and unconscious information processing. The implications from this are that one cannot assume that a change in the level of consciousness only alters the brain processes that are associated with conscious experiences. Previous research that has aimed to investigate how the brain generates conscious experiences by manipulating the level of consciousness should therefore be interpreted with caution, because the differences that have been found may well be related to unconscious information processing. Consequently, we suggest that use of the term “level of consciousness” is often ill-advised and terms like “wakefulness”, “arousal” or similar is more appropriate.
In study 2 we found that dexmedetomidine specifically alters conscious information processing, while unconscious processing was not significantly changed. This opens for the possibility that continued research on the effects of dexmedetomidine could help clarify the neurobiological basis of consciousness in a unique way. Current research indicates that dexmedetomidine primarily alters the level of the neurotransmitter noradrenaline. Noradrenaline is associated with several brain processes, including attention and memory. Noradrenaline is considered to qualitatively alter how nerve cells process information, while other neurotransmitters, for example acetylcholine and GABA, “only” alter their amplitude. Possibly, these and similar puzzle pieces can result in increased understanding of how the brain generates our consciousness. However, several questions remain before we can say with certainty that noradrenaline specifically alters conscious information processing (see below).
The data collection for study 3 (sleep deprivation) was delayed as a consequence of the corona pandemic, but is complete and data analyses are in progress. There are, however, currently no results available.
New research questions
An important part of the science of consciousness is to try to understand which individuals have the capacity for conscious experiences. This is highly relevant for, e.g., patients with brain damage and to reliably know that patients that are sedated for major surgeries will not have to experience the surgical procedures. Several “markers of consciousness” have been suggested in the scientific literature, but the underlying research have not previously taken unconscious information processing into consideration. The results from study 1 demonstrates that this is problematic. Given the experimental paradigm that we here have developed (the combined manipulation of level and content of consciousness) it is now possible to verify previous markers, or to develop more reliable alternatives.
The finding that dexmedetomidine specifically alters conscious information processing provides promising opportunities, because it may provide information on the neurophysiological mechanisms of consciousness. There are, however, several questions that need to be sorted out before strong conclusions can be made. One of the problems are that noradrenaline is associated with selective attention. Possibly, the effects we have seen in our data are due to altered attention rather than reflecting a direct relation between the levels of noradrenaline and conscious information processing. A second problem is that different neurotransmitter systems in the brain interact with each other. Thus, altered levels of noradrenaline can lead to altered levels of acetylcholine, dopamine, etc. Continued progress therefore hinges on that the relation between noradrenaline and conscious information processing can be verified.
Since this is the first time that both the level and content of consciousness have been manipulated simultaneously, it is important that the findings are replicated, but also that the generalizability is investigated. For example, it remains unclear if the effects from altered arousal on conscious and unconscious processing is the same if other stimuli, tasks, and manipulations of the content of consciousness, are used.
Dissemination of research and results
Results from the project has been, and will continue to be, published with Open Access in international peer-review journals. They have also been presented at international scientific conferences and local scientific events, as well as in teaching. Participation in scientific conferences has been negatively affected by the ongoing corona pandemic.
List of publications
Papers:
Fontan, A., Lindgren, L., Pedale, T., Brorsson, C., Bergström, F., & Eriksson, J. (2021). A reduced level of consciousness affects non-conscious processes. NeuroImage. doi: 10.1016/j.neuroimage.2021.118571
Eriksson, J., Fontan, A., & Pedale, T. (2020). Make the unconscious explicit to boost the science of consciousness. Frontiers in Psychology, 11:260. doi: 10.3389/fpsyg.2020.00260
Fontan, A., Lindgren, L., Pedale, T., Brorsson, C., Karampela, O., Bergström, F., & Eriksson, J. (in preparation). Noradrenergic activity may be a valid target for pharmacological manipulations of consciousness.
Conference presentations:
Fontan A., Lindgren L., Pedale T., Bergström F., Brorsson C., Eriksson J. (2019) Changes in the global state of consciousness affect brain activity related to conscious and non-conscious visual experiences differently. Poster presented at the annual meeting of the Society for Neuroscience, Chicago, USA, October 19-23.
Karampela, O., Fontan A., Lindgren L., Pedale T., Bergström F., Brorsson C., Eriksson J. (2022) Sedation: A probe to explore the neural mechanisms of consciousness. Poster to be presented at the annual meeting of the Organization of Human Brain Mapping, Glasgow, Scotland, June 19-23.