Is Emotion The Origin of Consciousness?
HomeUnderstanding consciousness is an inherently hard problem (Chalmers, 1995) with different approaches across philosophical, psychological and related fields. Generally defined, a conscious being has subjective experiences and is able to reflect upon their own existence (Frith, 2019; Colman, 2015). Amongst psychologists, this understanding is often divided into phenomenal consciousness, what ‘it is like to be you’ and access consciousness,our ability to reason and rationally guide our speech and behaviours (Block, 1995). In neurology, consciousness is often divided into (1) levels of consciousness, ranging from deep unconscious states (e.g. comas) to fully alert wakefulness, and (2) contents of consciousness, the information one is aware of at any moment in time (Eysenck & Keane, 2015). Locating the brain locus of consciousness (BLoC), which I will define as a singular region of the brain where consciousness originates, is a substantial challenge, but nonetheless, an important pursuit. Understanding this could help focus research within medical, technological, and ethical practices, potentially transforming approaches to mental health disorders, artificial intelligence, and neuroethics.
Empirical techniques, including visual, attention/memory, verbal, auditory, and sensorimotor tests, probe different aspects of consciousness and have led to the discovery of various neural correlates, including the frontoparietal network, dorsolateral prefrontal cortex and posterior cortical hot zones (Yaron, et al., 2022). Such empirical observations have given rise to various explanatory theories, including Global Neuronal Workspace Theory (GNWT), Recurrent Processing Theory (RPT), and Integrated Information Theory (IIT). These theories suggest that consciousness emerges from coordinated perceptual information processing across a distributed network of cortical and subcortical brain regions, rather than from a BLoC (Liaw & Augustine, 2023). However, one might also propose that, since our experience of consciousness occurs as a bound and coherent perceptual signal of sensory information, the empirically observed coordinated activation of brain regions across a distributed network must give rise to consciousness via some neural integration mechanism binding such information into a single signal of perception, i.e. a BLoC (Crick & Koch, 2005).
In this article I will briefly outline the empirical data andresultant distributed network theories of consciousness, before focusing directly on the question in hand and proposing the parabrachial nuclei of the pons,under the Free Energy Principle Theory of consciousness, as the strongest BLoC candidate (Solms, 2019).
This section offers an overview of the 3 most popular distributed theories of consciousness (DToCs) (Yaron, et al., 2022) and the empirical observations which underlie them. Ultimately, I aim to show their inadequacy and motivate space to explore theories in favour of the existence of a BLoC.
Global Neuronal Workspace Theory
GNWT is an extension of Global Workspace Theory (Baars, 2005) and proposes that conscious cognition emerges when information, processed in various subcortical structures, gains access to the global neuronal workspace of the frontoparietal network (Dehaene & Changeux, 2004).
Recurrent Processing Theory
RPT proposes that consciousness emerges from feedback loops between higher- and lower-level brain areas. Feedforward (unidirectional) processinghandles information in fragments. This only turns into coherent and conscious information when recurrent processing occurs. RPT functions via plastic changes to synaptic connections, a process mediated by N-methyl-D-aspartate-receptor-dependent feedback activations (Lamme, 2010).
Integrated Information Theory
IIT suggests consciousness arises from the brain’s ability to combine information from different domains of neural processing in a unique and indivisible way. This integration is quantified by the brain’s irreducible intrinsic cause-effect power,measured as its value (Tononi, 2004). is thought to peak in the posterior cortical hot zone (Yaron, et al., 2022).
Inadequacies in DToCs
It is evident that each theory presents unique translations of empirical observations, offering different neural modalities through which consciousness emerges. However, it is also the case that they align on the process through which these modalities cause consciousness to emerge – the coordination of perceptual stimuli across distributed networks of cortical and subcortical regions. Such DToCs are incompatible with the existence of a BLoC as they necessitate all regions working together to produce the phenomenon of consciousness.
I will present two major problems with these theories: (i) the empirical evidence supporting these theories originates from research shown to possess confirmation biases, and (ii) consciousness can be shown to exist without the cerebral cortical regions which each theory suggest are crucial for its emergence.
In a meta-analysis of n=412 studies investigating IIT, RPT,and GNWT between 2001 and 2019, Yaron, et al. (2022) presented clear evidence of systematic and consistent confirmation biases. Examined together, fMRI data across studies demonstrated that conscious perception results in activation across almost all regions of the brain. Yet, when fMRIdata is categorised by theory-type, distinct patterns of brain activation emerge which appear to only support the theory which that study aimed to empirically investigate (Yaron, et al., 2022). This suggests researchers might be neglecting or explaining away data that is incompatible with the predictions of their theory, or that each theory only explains a specific aspect of consciousness, with unique modalities of testing that cannot access other aspects. The latter conclusion is perhaps supported by the fact that, of all the experiments investigated, 86% focused on probing consciousness via its content using visual stimuli only, thus neglecting both,the level of consciousness, and other important sensory modalities like attention/memory,auditory and sensorimotor (Yaron, et al., 2022). This is a problematic observation and draws into question the efficacy of empirical observations used to support DToCs.
It is also the case that IIT, RPT, and GNWT place great significance on the role of the cerebral cortex in consciousness, specifically the prefrontal cortex, N-methyl-D-aspartate receptors, and posterior cortical hot zone regions. It is presumably uncontroversial to suggest that any theory weighted upon the functional role of a particular brain region for the production of consciousness is immediately falsifiable if the ablation of such structures do not result in a loss of consciousness. Consciousness has been shown to remain intact in patients with complete destruction to the very brain regions these theories specify as crucial for consciousness (LeDoux & Brown, 2017), further, children born without any cerebral cortices at all (hydranencephaly) exhibit rich conscious experience (Merker, 2007), and so do decorticate animals (Damasio & Carvalho, 2013). By extension it is therefore uncontroversial to state that IIT, RPT and GNWT (as defined in this article) are erroneous or at the very least, incomplete.
Despite the potential confirmation bias of each theory’s empirical data, when examined together, brain imaging data from Yaron, et al.’s (2022) meta-analysis suggested global neuronal activation likely co-occurs with consciousness. This is intuitive from a psychological perspective, as we know conscious perception comprises of the integration of multiple of sensory modalities (visual, auditory and sensorimotor) and sub-modalities (colour, pitch, temperature) dependent on different regions within the brain. However, since it is not entirely clear that consciousness is simply an emergent phenomenon of DToCs, there’s space to propose an alternative perspective, namely, a neural integration mechanism binding cognitive information into a single signal of perception. Or, as phrased by Crick & Koch (2005), a neural ‘conductor’ coordinating the ‘orchestra’ of global brain activation – a BLoC.
Crick and Koch (2005) proposed the BLoC could be the claustrum, a thin, irregular sheet of neurons located underneath the neocortex that sends and receives signals to almost all regions of the cortex. However,this proposition has since been shown implausible since research has demonstrated claustrum lesions do not always result in loss of consciousness (Chau, et al., 2015) and further, upon their surgical removal, patients have been observed to retain full long-term sensorimotor and cognitive functioning (Duffau, et al., 2007). Nonetheless, the idea of a neural conductor remains a plausible assertion.
A recent paper by Solms (2019) suggests the parabrachial nuclei of the pons (PNP), located in the brainstem core could be a strong alternative candidate for the BLoC. The likely involvement of the brainstem in consciousness was first observed via lesion studies within a brain region known as the extended reticulo thalamic activating system (ERTAS). ERTAS lesions resulted in the total eradication of consciousness, a phenomena first observed via cats (Moruzzi & Magoun, 1949) and subsequently replicated in humans (Penfield & Jasper, 1954). More recent studies have refined this locale further to the PNP, where small lesions resulted in the inducing of comatose states (Golaszewski, 2016).
Solms (2019) attempts to reconcile these empirical observations under the Free Energy Principle Theory (FEPT) of consciousness. FEPT posits that consciousness emerges from affect (our feelings)defined as responses to internal model prediction errors of external stimuli as we strive to maintain homeostasis. These errors are prioritised by their sensory significance, guiding actions and decision via differences in affect. From a theoretical perspective, FEPT aligns with Freud’s assertion that affect isintrinsically consciousness (Solms & Nersessian, 1999). Conscious experience requires that there is something it is like to be you (Nagel, 1980). When we reflect on perceptual stimuli more broadly, it is not necessarily the case that there must always be something it is like to see, hear or learn. For example, in masked stimulus experiments humans have been shown to learn about and act upon information presented visually, without conscious perception (Sid & Stanislas, 2007). However, it is entirely oxymoronic to suggest there is such a thing as feeling (or affect) without there being something it is like to feel. One might argue that all emotions are not necessarily conscious, but this would simply position affect as the conscious experience of emotion (Solms, 2022). In summary, ifwe wish to identify consciousness we must be guided by affect, as there exists no way to decouple the two phenomena; one is a foundational aspect of the other.
GNWT, IIT and RPT do not explicitly account for the importance of affect but the ERTAS, which joins together at the PNP, plays a crucial role in its cognitive emergence. This is supported by research on psychotropic medications which aim to adjust our moods and anxiety. Such studies have been shown to act via neuromodulators within the ERTAS nuclei (Meyer & Quenzer, 2005). Further, returning to the earlier example of hydranencephaly used to invalidate GNWT, IIT and RPT,children who exhibit conscious behaviour without possessing cerebral cortices notably possess intact brainstems, and further exhibit strong emotions and emotionally motivated behaviour (Merker, 2007).
It is likely, therefore, that the PNP is a strong candidate BLoC. Its centrality within the brainstem positions it well as a hub for integrating sensory information and modulating neurophysiological responses to prediction errors. The role of the PNP in autonomic functions and its extensive connections to both higher cortical regions and sensory systems aligns well with FEPT’s emphasis on internal model updating based on the full modalities of sensory input. Further, evidence from psychotropic medicine and lesion studies both suggest the PNP plays a crucial role in processing affect and maintaining a consistent state of consciousness.
I will close this article by addressing 2 strong potential criticisms of FEPT and PNP.
Critique 1 – The PNP Is Necessary but Not Sufficient for Consciousness Koch (2004) has suggested before that the brainstem is more likely an enabler, than origin, of consciousness. Likewise,one could propose that the PNP is necessary but not sufficient in the creation of consciousness as it relies on the perceptual stimuli received via the ERTASand from neuronal circuits linked to other cortical regions. Consciousness cannot arise from the PNP alone. It is therefore not the BLoC, and it is unlikely such a thing exists.
Critique 2 – The Hard Problem of Consciousness Remains Chalmers (1995) famously argues that consciousness cannot be fully explained functionally (purely physically)as such approaches fundamentally fail to address qualia (subjective experience)an important aspect of consciousness. Locating a BLoC should capture all aspects of consciousness, but since this is an impossibility, functional accounts of consciousness like FEPT are inherently incomplete.
A Response
To Critique 1, one could argue, based on the cases of hydranencephaly discussed earlier, that conscious awareness can primarily arise from brainstem activity, thus supporting the PNP’s candidacy as the BLoC. However, there are clearly additional and more particular philosophical dimensions to address. Defining the BLoC as the region of the brain where consciousness originates, the PNP would therefore have to be the first brain region to activate in conscious awakening. Such a position would not preclude the involvement of other regions such as the ERTAS in the subsequent sustaining, or maintenance of consciousness. Coenen (1998) demonstrated that the mesencephalic reticular formation of the brainstem is the root of activation and arousal for the entire thalamocortical system. This results in an arousing state characterised by a rise in thalamocortical activity and an influx of sensory information to higher brain centres, leading to perception and conscious awareness. Thus, suggesting the brainstem could be the first brain region to activate in conscious awakening. Nonetheless, it is likely greater empirical evidence is needed to support such a claim and thus, future research should explore it further.
To Critique 2, Chalmers (1995)has argued that functional explanations of consciousness fail to account for qualia because of the “explanatory gap” which exists between functionalist accounts of consciousness such as perception, memory, and language and the essence of conscious experience. However, FEPT avoids this functionalist trapas it focuses on affect. Affect bridges the explanatory gap and sufficiently accounts for the qualia of consciousness because it reflects the intrinsic emotional and subjective qualities that are central to the phenomenological aspects of consciousness. Affect, as posited by FEPT, is fundamentally about the experience of feelings, which are immediately known and felt by the individual. This approach directly engages with the qualia by explaining how affective states are shaped by the brain's predictive coding and error correction mechanisms (Solms, 2022).
I acknowledge that there are likely more critiques to the position of FEPT and PNP as a candidate BLoC, including potential empirical methodological limitations, alternative theories and the generalisability of such across different species and developmental stages. However, it is clear that this is a promising position at present, not beyond useful consideration and worthy of future empirical and theoretical pursuit.
In conclusion, locating the BLoC is a highly technical but valuable endeavour within the realm of psychological and neurological research. This article compelsa revaluation of classical assumptions towards DToCs such as GNWT, IIT, andRPT, due to the questionable nature of empirical data supporting them and the existence of cases where consciousness persists in absence of cerebral cortical regions. Such shortfalls underscore the plausibility of a more centralised mechanism of consciousness – the BLoC – and evidence suggests that this could be located at the PNP within the brainstem core. The PNP integrates and modulates sensory information and neurophysiological responses from the ERTAS and other equivalent neuronal circuits, aligning with the FEPT of consciousness which highlights the central role of affect. The potential of PNP as a strong candidate BLoC can be shown to withstand initial critiques but future research is necessary to substantiate its role in consciousness.
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