How is the Brain’s Neuronal Activity Transformed into Mental States?
Unlocking the Brain
As a philosopher, neuroscientist, and psychiatrist, Georg Northoff has thought a great deal about consciousness. Here he shares the essence of his understanding of how consciousness comes about.
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The Subjective Character of Consciousness
Everybody knows what it is to be conscious. You experience it continuously during the day and even during the night while dreaming. When reading this article, for instance, and the lines of the text, you are conscious of the contents written there; conscious of the words, the sentences, and their meaning. More specifically, you perceive the words and sentences in a conscious mode—perhaps feeling certain emotions such as anger or frustration at a seemingly banal beginning—and you may become conscious of thoughts and cognitions tempting you to contradict the definitions given there, or telling you to move on to something more gripping. Ultimately, even one’s own self (the one who is reading these lines) enters consciousness, yielding what is called “self-consciousness”.
Consciousness is such a basic phenomenon that any definition seems superfluous. Nevertheless, if we want to understand how consciousness is yielded, we need at least to somehow determine what it is we are searching for. Otherwise we remain blind about our direction.
So what is consciousness? Let me first give a tentative definition. The philosopher Thomas Nagel (1974) characterized consciousness as having a certain “what it is like” quality. The concept of “what it is like” describes that experience, and thus consciousness goes along with a particular quality, a phenomenal-qualitative feel known as qualia. For example, if you read a book with a red cover, you experience the redness of the book’s red color in terms of this phenomenal-qualitative feeling: you have a quale of the color red.
At first you may just perceive or observe the red color, you do not experience a particular quality; the red color is purely quantitative. But that changes once you switch from your third-person mode of observation to a first-person mode of experience. Now you experience the color as part of your own self, and you experience the redness of the book’s cover. This is the moment when philosophers like to speak of qualia. Hence, the phenomenal-qualitative feel, the qualia, must be regarded as a hallmark feature of experience and therefore of consciousness.
Imagine you like eating chocolate. You see the chocolate in the store and start to develop an urge or craving. You buy the chocolate and taste it piece by piece. You enjoy the chocolate—especially bitter chocolate is your favorite—and you enjoy and dwell in the bitterness of the taste. This is your subjective experience, the bitterness of the chocolate that goes way beyond its merely objective bitter features. The bitterness is your subjective experience of the objectively bitter chocolate. Since you love bitter chocolate so much, you may subjectively experience the bitterness in your first-person perspective to a much stronger degree than is objectively present in the chocolate itself (independent of your tasting the same chocolate). There is thus a “what it is like” for you to experience and taste the bitterness of the chocolate.
Consciousness in this sense is subjective and private rather than objective and public. Due to its subjective and private character it cannot be observed by others; nor can we observe it in the brain, where we see nothing but neural activity, not qualia or experience. Observing changes in the brain’s neural activity provides some clues, but what remains unclear is how, why, and when the brain’s neural activity—which is purely nonconscious by itself—is transformed into a conscious state. Hence the old problem: the quest for neuro-mental transformation is here specified and condensed in the question of why and how neuronal states can yield conscious states.
Conscious Versus Unconscious Contents
How then can we research consciousness in neuroscience? One starting point is the content of consciousness. For example, referring again to the red book, we are conscious of its color. The book is thus the content of consciousness, also known as the phenomenal content: our consciousness is always “consciousness about contents”. Yes! These can include events, persons, or objects in the environment. Alternatively, the contents of consciousness can also consist of our own thoughts or some imaginary scene about persons or objects or events in your dreams when you sleep.
These contents can now be taken as the starting point for neuroscientific investigation. Neuroscience can, for instance, investigate the neuronal differences between contents that are conscious and the ones that remain unconscious. How can we further illustrate this? The unconscious content may still exert an impact on our behavior; for instance, a person (“Lucy”) may avoid going on bridges because as a young child she fell down from a bridge and broke her right leg, but when avoiding bridges as an adult she may not be aware that this event in her past makes her avoid bridges now. However, it is possible for our unconscious to become conscious and so realize that it is because of our earlier experiences (such as falling down from a bridge) that we avoid crossing them. Another example concerns a man (“John”) who, as a result of a motorbike accident, is in a vegetative state (VS); and should he ever emerge from his VS, he is likely to avoid motorbikes at all costs, even if he can’t remember exactly why.
These examples illustrate that the same content (whether a particular event, person, or object) can be presented both in a conscious mode with subjective experience and in an unconscious mode. The neuronal difference between the conscious and the unconscious mode must then be related to consciousness. However, the brain’s sensory functions only allow for the processing of the sensory contents themselves, like the stimuli related to the color red and the chocolate. In contrast, sensory processing by itself does not explain the specifically subjective component, the “what it is like” that is associated with and characterizes the conscious experience of these contents. Hence, an additional neuronal process is needed to account for the neural correlates of consciousness.
Level of Consciousness Goes Rest
Many different theories (cyclic processing, global workspace, information integration) have been postulated to account for conscious contents as distinct from unconscious contents. However, consciousness is more than just contents. It is also about arousal, or the level of consciousness. This leads us away from the mere stimulus-induced activity, as related to contents, to the brain’s intrinsic (or spontaneous) activity. The level of consciousness is, for instance, most severely reduced in patients with VS who have lost consciousness and are no longer able to move and communicate.
What in the brain decides whether a given stimulus is provided access to the various regions and networks? Earlier philosophers like Descartes assumed the mind was central at this point. His philosophical successors, such as the German philosopher Immanuel Kant in the nineteenth century and more recent philosophers in our time like Shawn Gallagher (2000) or Dan Zahavi (2005), assumed a self (or subject) that allows or prevents access of stimuli to the brain. Today we have plenty of evidence to show that there is neither a mind nor a self or subject distinct from the brain: it is the brain itself—and, more specifically, its intrinsic activity—that may provide or prevent environmental stimuli from being properly processed. So, it is the brain’s intrinsic activity that plays a vital role in deciding whether we are conscious or unconscious.
How does the brain’s intrinsic activity do this? Functional connectivity describes the highways in the brain through which the different regions can communicate with each other. These highways seem to be reduced in VS. Variability is about the degree in change of the amplitude of activity and the degree of traffic and how it changes during the day. In VS, the amplitude of activity and hence the degree of traffic no longer change as much, they remain more or less the same across time. This means that the brain’s resting state activity is no longer as variable; and this in turn means that it can no longer react to novel stimuli or adapt its activity level.
Imagine you speak only five words of English. This makes it hard for you to properly respond to other people in a flexible and adaptive way. The same seems to be the case in VS. In this case, however, the variability of the brain’s resting state activity is reduced, which makes it hard if not impossible for the brain’s resting state to react in a flexible way to different stimuli, let alone assign consciousness to them.
Most importantly, decreased variability in midline regions’ resting state activity predicts the degree of self-specific activity observed in these patients—which, in turn, as described above, predicts the level of consciousness, step by step. If the brain’s resting state is no longer variable, it cannot relate the extrinsic stimuli to itself and there is reduced self-specific activity. Further, if the stimuli’s relation to the resting state—that is, if their self-specificity is reduced—they can no longer be assigned or associated with a certain level of consciousness. This is what the correlations tell us. Accordingly, the resting state activity and, especially, its variability can impact the level of consciousness—though apparently not in a direct way but rather in an indirect way as mediated by the degree of stimulus-induced or task-evoked activity.
Let us put this in more formal and technical terms. The resting state activity may not be considered a sufficient condition of the level of consciousness—a neural correlate—but rather a neural predisposition. Neural correlate would mean that the resting state itself is directly related to the level of consciousness, but that was not the case: we did not find a direct correlation of resting state activity with the level of consciousness. On the other hand, we did observe that the resting state variability correlated with the degree of self-specific activity, and this in turn predicted the level of consciousness. Hence, the resting state is indirectly related to the level of consciousness with task-evoked activity during self-specific stimuli as an intermediate: the higher the resting state’s variability, the higher the degree of self-specificity and the higher the level of consciousness. Without the resting state there would be no self-specificity, and without self-specificity there is no consciousness. The resting state and its variability may thus be a necessary condition, though not a sufficient condition by itself, of the level of consciousness. As I have said, it is not a neural correlate of consciousness but a neural predisposition of consciousness. The resting state does not cause but rather predispose the level of consciousness.
What then are the features of the resting state activity that predisposes or makes consciousness possible? Specifically, how does the resting state assign a certain level of consciousness to its contents? This is the question for the mechanisms underlying the interaction between resting state and stimulus: the so-called rest-stimulus interaction. The resting state must be in a certain state to allow it to react to the stimulus in such a way that the latter can be associated with consciousness. This shall be explored in the following.
Rest-Stimulus Interaction and Consciousness
How is rest-stimulus interaction related to consciousness? The research group around the German-French neuroscientist and neurologist Andreas Kleinschmidt investigated what is described as bistable perception—this refers to your ability to perceive the well-known optical illusion that shows either a vase or an old woman. It describes the fluctuation between two different perceptions with regard to one and the same stimulus.
So how is bistable perception possible? Kleinschmidt and his colleagues (see Sadaghiani, Hesselmann, & Kleinschmidt, 2009) observed that the degree of preceding resting state activity in those regions processing the vase and the women predicts whether one perceives the stimulus (in this case a picture) as a vase or the face of an old woman. If, for instance, the resting state activity prior to the presentation of the picture is high in the region that processes faces, the fusiform face area, the subject will see the picture as an old woman. If, in contrast, preceding activity levels are high in the regions that process inanimate objects, the subject will perceive a vase rather than an old woman’s face. Hence, the resting state activity itself—that is, its level prior to the actual stimulus—seems to be central in selecting the kind of contents for the assignment of the level of consciousness.
The interaction between resting state and extrinsic stimulus thus allows for interaction between level and content of consciousness. Specifically, the level of pre-stimulus resting state activity is central in determining the level of consciousness that can possibly be assigned to the subsequent stimulus and its respective contents. The studies are concerned with what is described in the current literature as the neural correlates of consciousness (NCC). Since they target consciousness with regard to specific contents, one can speak of content-NCC and how that is related to level of consciousness or level-NCC.
The quest for the level-NCC implies a distinction between consciousness and unconsciousness. However, these studies do not tell us anything about the distinction between consciousness and nonconsciousness, and that is the hard problem. In order to address the latter distinction, we need to account for the temporal and spatial structure of the brain’s intrinsic activity. This may tell us why and how the brain can assign consciousness to the various contents and their extrinsic or environmental stimuli, the brain processes. By constituting a temporal and spatial structure, the brain’s intrinsic activity has a tool or means that it imposes upon all extrinsic stimuli. As such, the brain’s intrinsic activity may provide a grid, template, or schemata along whose lines all subsequent forms of neural activity, intrinsic and extrinsic, are organized and structured.
That the brain’s intrinsic activity seems to provide an organizational template has already been described by the American psychologist and neuroscientist Karl Lashley (1890-1958). He said, “A second point of major importance is that the nervous system is not a neutral medium on which learning imposes any form of organization whatsoever. On the contrary, it has definite predilections for certain forms of organization and imposes these upon the sensory impulses that reach it. In its functional organization, the nervous system seems to consist of schemata or basic patterns within which new stimuli are fitted.” (Lashley, 1949, p. 35).
What exactly is meant by organizational template? The organizational template describes a spatial and temporal structure of the brain’s intrinsic activity. The spatial structure is about different neural networks that are constituted in the resting state. There is a network in the middle of the brain, the default-mode network, which is in charge of self-related processing. A network at the edges of the brain, the executive control network, allows for cognition and action; the salience network assigns salience and relevance to stimuli, while the sensorimotor network includes various sensory and motor regions. What about the temporal structure? The resting state shows continuous change in its activity level, and these changes can occur in different frequency ranges that may or may not be coupled or linked to each other. Such coupling between different frequency ranges provides a certain temporal structure, template, or grid.
Neural Predisposition Versus Neural Correlates of Consciousness
How are these schemata of intrinsic activity related to consciousness? Well, once again we must admit that for now we don’t know. We do know that there is a certain temporal and spatial structure in the brain’s intrinsic activity, but we just don’t know how it’s related to consciousness.
And how is the spatiotemporal structure of the brain’s intrinsic activity transformed into the mental features of consciousness? One of the central phenomenal features of consciousness is spatial and temporal continuity. Your consciousness, for instance, never stops: you perceive the book in front of you, for example, then you glance over to the bottle of wine, and after that to the cheese standing on the table. Accordingly, spatial and temporal continuity describe how contents of consciousness are always already embedded in a spatiotemporal grid that provides temporal flow and spatial integration in our experience. Instead of being segregated in time and space, therefore, the different contents are spatially and temporally linked in our consciousness.
The contents of consciousness flow within the navigational grid of a person’s brain. Despite their occurrence at different discrete points in physical time, we nevertheless experience a temporal continuum, a transition, between the different contents in our consciousness. This temporal continuum in consciousness does not seem to correspond one-to-one to objective time or its discrete points as we observe them in third-person perspective. Rather, we experience a continuum between different discrete points in our consciousness and what phenomenally is described as dynamic flow (James, 1890).
While there has been much debate about time and consciousness, there has been less discussion about the experience of space in consciousness. Analogous to time, one may want to make a similar distinction; as there is temporal continuity, so there is spatial continuity in our consciousness. We see, for instance, the table standing in front of us in continuation of the floor on which it is standing, and continuous to the chairs standing around it. The contents in consciousness are not experienced at their different discrete points in physical space. Instead, they are embedded and integrated into a spatial continuum with multiple transitions between the different discrete points in physical space. As in the case of time, the contents are woven into a spatial grid or template that emphasizes continuity and transition over discontinuity and segregation.
Form of Consciousness Goes Spatiotemporal
How are a spatiotemporal grid and its spatial and temporal continuity constituted? One may now assume the brain’s intrinsic activity to be central in constituting the spatiotemporal grid. If so, one would assume that the neuronal features underlying the spatial and temporal structure of the brain’s intrinsic activity, discussed above, would account for the spatial and temporal features as we experience them in consciousness. One would then expect the temporal distances experienced between different contents in consciousness to correspond to the temporal distances constituted in the temporal structure of the brain’s intrinsic activity.
If so, the intrinsic activity and its spatiotemporal structure provide the form or structure of consciousness. The concept of form refers to the structure or organization within which the various stimuli from outside the brain interact with and are integrated within the brain’s intrinsic activity. The intrinsic activity and its spatiotemporal structure impose themselves upon a stimulus, integrating it, and it is this integration that may make it possible to assign consciousness to the stimulus. Importantly, the intrinsic activity and its spatiotemporal structure organize the incoming sensory stimuli—the former orders and groups the latter and integrates them into its spatiotemporal grid. That spatiotemporal integration in turn makes possible the assignment of consciousness to a single sensory stimulus and its respective contents. Consciousness may then be conceived in a spatiotemporal way: without the spatiotemporal grid or form of the brain’s intrinsic activity, consciousness would remain altogether impossible.
What is it that the resting state provides that makes consciousness possible? Here, and in Unlocking the Brain (Northoff, 2014a, 2014b), I argue that the intrinsic activity and its spatiotemporal structure provide the form of consciousness. And it is this form that first and foremost makes possible the transformation of a purely neuronal state into a conscious or mental state. Accordingly, by providing such form, the brain’s intrinsic activity and its spatiotemporal structure make possible or predispose consciousness: it is a necessary but nonsufficient condition or neural predisposition of consciousness (NPC), rather than being sufficient by itself like the neural correlates of consciousness (NCC). In the case of Lucy and John the resting state’s spatiotemporal structure seems to be frozen—it is not active due to lack of energy. Hence they lack the form of consciousness as the neural predisposition of consciousness.
Hard Problem and Soft Solution
Let us conceive what philosophers describe as the hard problem. What is it? In a nutshell, the hard problem raises the following question: why and how is there consciousness rather than nonconsciousness? The hard problem touches upon what I have described as neuro-mental transformation—that is, what, where, how, and why does a purely neuronal state transform into a mental state like consciousness?
How are the brain’s intrinsic activity and its suggested spatiotemporal structure related to the hard problem? The answer is clear: because the brain shows intrinsic activity which, because of its presumed spatiotemporal structure, predisposes possible consciousness. The predisposition for possible consciousness can be transformed into the manifestation of actual consciousness in the “right” context—that is, the right extrinsic stimulus and its right interaction with the intrinsic activity.
While possible consciousness is supposed to be mediated by the neural predispositions, the intrinsic activity and its spatiotemporal structure, actual consciousness may be related to neural correlates. Neural correlates refer to the sufficient conditions of actual consciousness. Both neural predispositions and neural correlates may be related to different neuronal mechanisms that have to act in conjunction in order to constitute consciousness rather than nonconsciousness.
In short, I assume the conjunction of neural predisposition and correlates as an empirical answer to the hard problem. Only if both go together will we be able to fully explain consciousness. The neural predispositions will account for the necessary conditions of possible consciousness while the neural correlates will reveal the necessary and sufficient conditions of actual consciousness.
This is an empirical answer to the hard problem. However, it’s nothing but a soft solution for the philosopher, whose real concern is usually metaphysical issues—the hard solutions. Yet even such a soft solution may still be of use to the philosopher. Why? The empirical solution sketched here may provide some clues. By pointing out the brain’s intrinsic activity and its spatiotemporal structure as the neural predisposition of consciousness, we may be able to develop a different methodological approach to the mind-brain problem. It allows us, for example, to replace the mind, as the methodological starting point for metaphysical mind-brain reflection, with the brain and its intrinsic features. Once we are clear about the brain’s intrinsic features, namely those that define the brain as brain as distinct from the mind and other organs, we may investigate how the existence and reality of those intrinsic features are related metaphysically to mental features.
This short discussion shows that consideration of the brain’s intrinsic activity is not only important in empirical terms in neuroscience, namely to understand the neural mechanisms underlying consciousness, but that it is also highly relevant for philosophy and the metaphysical quest for an understanding of the mind-brain relationship. In the same way that the intrinsic activity changes the neuroscientific approach to consciousness, it is also a game changer in philosophy when it comes to the brain-mind problem. Thus, instead of asking the question, “How is the mind related to the brain?” we can now ask, “How is the brain’s intrinsic activity transformed into mental features?”
From this perspective, the methodological starting point of philosophy is not only different but reversed: traditionally, in philosophy, we start with the mind and continue from there to the brain, while now we start with the brain itself (its intrinsic activity) and extend from there to mental features like consciousness. What is described as a metaphysical problem between two different existences and realities, mind and brain, is now converted into a transformation problem: how the brain’s intrinsic activity transforms neuronal activity into mental features.
The traditional philosopher may be puzzled. He longs for answers to the mind-brain problem: how the metaphysical existence and reality of the mind is related to the one of the brain. I do not provide such answers. Instead, I propose an escape from the question that makes any subsequent mind-brain answer or solution futile. If there is no meaning to such a question, there can be no meaningful answer.
Is Consciousness a Basic Function of the Brain’s Resting State?
Traditional philosophers might now raise the question of what is going on in John’s and Lucy’s minds in their vegetative state. Philosophers past (Descartes, Kant, etc.) and present (e.g., Searle, Rosenthal) generally conceive of consciousness as a higher-order function that may be related empirically to cognitive functions such as memory and attention. Others (see, e.g., Thompson, 2007) emphasize the role of the body and its sensorimotor functions: due to these, we are based and located and in continuous contact with the world, which, in turn, makes consciousness first and foremost possible. Without any such location and contact with the world, no cognitive function would be able to generate consciousness. Hence, so the advocates of this position claim, we need to consider the body and its sensorimotor functions as the most central condition of consciousness. Rather than locating consciousness in the higher-order functions of our cognition, consciousness must be associated with lower-order functions such as perception and action.
The findings and picture sketched here seem to be even more radical. Is consciousness a function of the brain’s resting state? If so, consciousness must be conceived as a most basic and fundamental function of this resting state. Since the brain’s resting state activity is spontaneously ongoing, it is always already there and occurs prior to and independently of the instantiation of sensorimotor and cognitive function. Consciousness can therefore neither be conceived as a higher-order cognitive function nor a lower-order sensorimotor function. Instead, just as the brain’s resting state provides the basis for any subsequent stimulus-induced activity, so consciousness provides the basis for any subsequent sensorimotor and cognitive function. Let us wait though for future empirical data and see whether they support such a view of consciousness as a function of the resting state’s spatiotemporal structure. If that holds, we will need to radically reconceptualize our view of consciousness as a higher-order function of our cognition or a lower-order function of perception and action. Rather than looking upwards to our higher-order functions, we would instead look downwards to our brain’s resting state activity. Deep down in the brain itself and its intrinsic activity, we can find the origin or source of consciousness, its neural predisposition. We should not let ourselves be confused by the colorful forms of stimulus-induced activity related to the brain’s various sensorimotor and cognitive functions. They are nothing but a specification of consciousness that is already predisposed by the resting state itself and its spatiotemporal structure. Accordingly, to trace down consciousness in the brain, we must understand the spatiotemporal structure of its intrinsic activity. What must the spatiotemporal structure look like in order to predispose consciousness? This is what may unlock the mystery of the brain, hence the title of my recent two-volume book Unlocking the Brain (Northoff, 2014a, 2014b) as well as Minding the Brain (Northoff, 2014c), which highlights the central role of the brain in philosophy.
Gallagher, S. (2000). Philosophical conceptions of the self: Implications for cognitive science. Trends in Cognitive Science, 4(1), 14–21.
James, W. (1890). The Principles of Psychology (Vols. 1–2). London, UK: Macmillan.
Lashley, K. S. (1949). Persistent problems in the evolution of mind. The Quarterly Review of Biology, 24(1), 28–42.
Nagel, T. (1974). What is it like to be a bat? The Philosophical Review, 83(4), 435–450.
Northoff, G. (2014a). Unlocking the Brain: Volume 1: Coding. Oxford, UK: Oxford University Press.
Northoff, G. (2014b) Unlocking the Brain: Volume 2: Consciousness. Oxford, UK: Oxford University Press.
Northoff, G. (2014c). Minding the brain: A guide to neuroscience and philosophy. London, UK: Palgrave Macmillan.
Sadaghiani, S., Hesselmann, G., & Kleinschmidt, A. (2009). Distributed and antagonistic contributions of ongoing activity fluctuations to auditory stimulus detection. The Journal of Neuroscience, 29, 13410-13417. doi:10.1523/JNEUROSCI.2592-09.2009
Thompson, E. (2007). Mind in life: Biology, phenomenology, and the sciences of mind. Cambridge, MA: Harvard University Press.
Zahavi, D. (2005). Subjectivity and selfhood: Investigating the first-person perspective. London, UK: The MIT Press.
An Issue of the Heart
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The Neuropsychotherapist Special Issues are anthologies of articles that have been published in the monthly magazine The Neuropsychotherapist.
This special issue is all about the heart... A wonder of complexity is the human being—something that continues to be a source of fascination and frustration for those of us who have set ourselves to understand human behaviour. This special issue focuses on the heart, an organ with a profound influence over our mental lives.
We are all familiar with the heart in its classical biological role as pump circulating vital oxygenated blood through the body. But how many are versed in its neural and bioelectromagnetic influence upon our brains? Research has revealed the heart even radiates an influence on those around us via electromgnetic fields. In the past such claims might have been dismissed as mere New Age fancy, but with ever more sophisticated and sensitive instruments, formal studies in recent years have demonstrated that our bodies have amazing multidimensional fields of awareness and influence. These findings about the heart continue to add weight to the argument that in the counselling room it is the therapist’s unconditional positive regard, warmth, and personal coherence more than any technique that make for effective therapy. It makes one wonder what the focus of training should be for new therapists—will courses become more focused on students developing personal coherence, practising attitudes of genuine care and compassion, and understanding what they are radiating to clients from their hearts?
Neuropsychotherapy, and the multidisciplinary integration that it stands for, is part of an important paradigm shift in medicine. Likewise, the focus on matters heart–brain in this issue reflects an important shift of understanding in the broader field of health. The study of any one bodily system—even the central nervous system in the case of psychologists—leaves us in the dark on many levels for many phenomena. It is our hope that you will come to appreciate the wonderful, so often implicit influence the heart has on our emotions and relationships, and that we will become more conscious of being authentic and coherent—for our clients and also for ourselves.