link between Self and neural responses to heartbeats

Posted comment on ´ Neural Responses to Heartbeats in the Default Network Encode the Self in Spontaneous Thoughts` by M. Babo-Rebelo, C.G. Richter and C. Taillon-Baudry and published in Journal of Neuroscience 27 July 2016 36 830) 7829 doi 10.1523/JNEUROSCI,0262-16.2016

SUMMARY

Babo-Rebelo, Richter and Taillon-Baudry`s article describes the Default Network (DN) as being associated with self-related cognition and physiological processes such as bodily state monitoring and autonomic regulation. These are described as functionally coupled because Selfhood is grounded in the neural monitoring of internal organs such as the heart.  In their study, the authors measured neural responses evoked by heartbeats (HERs) when 16 right-handed subjects who had been pre-trained in the test method, allowed their minds to freely wander after a period of visual fixation (a black circle with a black dot in the centre on a grey background). This period was interrupted by a visual stimulus (8 white dots presented for 200ms) at random intervals (13.5 to 30 secs) and the subjects were asked to score the self-relatedness of their thoughts occurring at the time of the interruption.

Self-relatedness was assessed from the first-person perspective, the subject (I) in the thought and this was termed ´Actor/Author` and the extent to which the ´author` was thinking about himself, termed ´Me` and ´Content`. The subjects were asked to use high ratings in the case of consideration from their own viewpoint and low when considering from someone else`s viewpoint or in the case of the ´Me` thoughts something external to them.  The authors found that both ´I` and ´Me` results were significantly positive suggesting that the scales used may have represented the same notion of Self. The interrupted thoughts were also rated according to emotional intensity (pleasant or unpleasant and termed ´Valence`), and relevance to past, present or future events on a scale from a few hours to several weeks (termed ´Time`). In these cases the responses were recorded by moving a cursor along a scale or by ignoring it if the subject had no response or were unable to quantify the response. Babo-Rebelo, Richter and Taillon-Baudry found that there was slight biasness towards high self-relatedness in the ´I` test to both the present when rating Time and pleasantness in rating Valence.

The test results produced showed that HERs scores were significantly different for high and low trials for ´I` thoughts and also for ´Me` thoughts over medial frontal sensors. No difference was found for the Time and Valence studies. There were spatial and temporal variations between the ´I` and ´Me` results and so further investigation was required since the study could have been capturing an unified self-relatedness of thoughts with any differences the result of personal rating differences of the subjects. A re-classification of the ratings on the Self scale gave no significant differences, but a study of heartbeat-by-heartbeat cluster amplitude and the raw Self-related rating at each investigated thought gave significant differences. The authors found no covariation however between self-relatedness and peripheral autonomic measures such as heart rate, heart rate variability, pupil diameter and blink response, electrodermal activity, respiration rate and phase, or alpha brain waves.

Babo-Rebelo, Richter and Taillon-Baudry continued their study by relating the interrupted thoughts to neural measurements of two brain areas of the DN that of the ventral precuneus and the ventromedial prefrontal cortex. They found HERs differed significantly along the ´I` scale in the left ventral precuneus with activity centering on the left precuneus and extending dorsally and posteriorly to the cuneus and calcarine sulcus. However, the HERs could only be detected in the left ventromedial prefrontal cortex when the Self was the subject of the ongoing thought. In the case of ´Me` thoughts then the study produced only differential HERs when the subject was the object of the ongoing thought and in this case activity was located in the left ventromedial prefrontal cortex centering on the left frontal medial orbital gyrus and extending posteriorly and dorsally to the left anterior cingulate and rectus gyri. The results were verified with surrogate heartbeats, ECG, personality (aspects such as self-consciousness scale, daydreaming frequency scale, trait anxiety inventory) and interoceptive ability.

Therefore, Babo-Rebelo, Richter and Taillon-Baudry concluded that the two areas, ventral precuneus and ventral medial prefrontal cortex, are differentially activated by heartbeats and part of the DN and that there is a link between Selfhood and neural responses. Therefore, they suggested that physiological and cognitive functions have to be considered jointly in the DN. They found that the ventral precuneus is associated with ´I` thoughts and this correlates to activity in episodic memory retrieval, perspective, body ownership, self-location, spatial navigation, imagination and future planning.  In comparison, the ventral medial prefrontal cortex is related to ´Me` thoughts and it is known that this area is important for monitoring of the visceral organs (including heartbeats). It is not a direct target of visceral inputs, but is functionally connected to the visceral centres of the brain and is involved in autonomous functions. Therefore, the ventral medial prefrontal cortex may be receiving visceral information through one or more cortical relays, which could explain the longer latency of the effect observed in the ventral precuneus. It was not possible for the authors to determine how the latency difference in transient neural responses to heartbeats in both areas directly relate to a differential time course of the ´I` and ´Me` dimensions in spontaneous thought that probably developed over seconds and this remains a topic for debate.

The authors concluded that the functional coupling between HERs and self-relatedness could stem from different mechanisms. HERs could directly contribute to the specification of the Self. It would contribute to the constant update of a neural reference frame centered on the subject’s body and hence, would serve as a basis for the development of self-relatedness. However, although the authors` results support this view other hypotheses were also considered. For example, self-related thoughts could induce an internally directed shift of attention leading to an amplification of processing of internal signals including heartbeats. This hypothesis was discounted by the authors since explicit orienting of attention towards heartbeats would alter the activity in other brain areas such as the insula, somatomotor sensory system and dorsal anterior cingulate cortices. No changes in activity were observed by Babo-Rebelo, Richter and Taillon-Baudry. Another explanation was given in that the HER covariation with self-relatedness was a byproduct of self-related processing. The neurons responding to heartbeats were being modulated by the neurons encoding self-relatedness. If this hypothesis is correct then the authors surmised that the HERs are modulated by the self-relatedness of spontaneous thoughts but have no direct consequence on the contents of those thoughts. This was determined by the authors as being very difficult to achieve. For now, they concluded that certain areas of the DN are engaged in physiological regulation, thus providing an explanation for its high basal metabolic rate, persistent activity in early sleep stages and its conservation across species.

COMMENT

After so many years of research and discussion, we are still not able to give definitive biological scientific explanations for consciousness, thinking and memories for example. Therefore, what makes this article interesting is that it links consciousness, something that is to date a biological mechanistic mystery, to a physiological process that is explainable, observable and adaptable, that of heartbeats. The authors of the article, Babo-Rebelo, Richter and Taillon-Baudry, found in their investigation that the activities of certain brain areas are associated with a change in consciousness according to thoughts occurring at the time and that, neural responses of these specific areas to heartbeats were affected. Therefore, something that is physical is ´rooted` to something that is mental and because the latter affects the former then concerns about the way some experimentation is carried out must arise. The interpretation of brain area activity and connectivity results maybe needs to be adjusted or experimental controls put in place that are robust enough to account for discrepancies of the thought processes of the various test participants at the time of experimentation.

For now we assume that study results are correct and therefore that the neural responses to heartbeats in two particular brain areas are different depending on the types of thinking being carried out by the subject in the test period. This article involves the Default Network (DN) also known as the Default Mode Network which is a set of brain regions which have a high metabolic rate even at ´idle` and which is switched off in task-orientated processing, but important where awareness of the Self is required. The authors looked at two areas in particular: that of the ventral precuneus (PC) and the ventromedial prefrontal cortex (vMPFC). The PC is located in the posteromedial of parietal lobe and is a highly connected area and a hub between the prefrontal and parietal areas. It consists of many distinctive areas which are linked to specific functions.  General functions include responsibility for visual sensory attentional information, episodic memory (linked to PFC), visuo-spatial processing, the Self and certain aspects of consciousness (eg. reflective Self-consciousness). The ventral PC is linked with the Self, the past and future, spatial navigation (motor imagery and shifting attention to motor targets whereas the dorsal part is associated with involuntary awareness and arousal. In comparison, the vMPFC is a part of the larger prefrontal cortex which is associated with lots of cognitive functions including memory and attention. The vMPFC itself (otherwise known as the orbitofrontal cortex) is linked with Self processing, emotional information, reward and value eg. the ability to assess according to one`s own objectives, formulating criteria etc. for decision-making, and control of stress through inputs from the PFC.

Babo-Rebelo, Richter and Taillon-Baudry found that elements of DN heartbeat connectivity were different according to the thoughts in ´idle` ie.  neuronal awareness of the bodily process was different according to what angle of thought was occurring at the time. They found that ´I` thoughts were linked to neural responses to the heartbeats in the area of the precuneus whereas ´Me` thoughts produced a response in the vMPFC. For their experiment, the authors defined Self-relatedness as the ´I` when the participant was the agent or subject in the thought and therefore this group included thoughts from the first-person perspective. A high ´I` rating was given for the thought ´I am thirsty` for example and low for thoughts such as ´It´s cloudy`. ´I` thoughts defined what the participant (the ´I`) wanted. On the other hand, ´Me` thoughts were defined as when the participant thought about himself/herself. For example, ´I am thirsty` or ´I should be more concerned` were rated high whereas thoughts directed towards something or someone else such as ´It´s raining` or ´She`s coming here on Monday` were given a low rating. ´Me ` thoughts defined the Self as what I am in the community. I must admit that I am not clear about distinguishing between ´I` and ´Me` thoughts in this way since I believe that both relate to the person in question. They may relate to real things either past or present, relate to unreal things such as things that will happen in the future or intentions, but they both relate to me, the Self. Therefore, defining ´I` and ´Me` thoughts appears to me more semantics. I accept that ´I am thirsty` requires bodily awareness and relates to the present and ´I will go to the bank tomorrow` involves more higher order brain areas with no physical awareness, but both relate to ´I/Me`, the person, the individual and both require my memories, my processing capability, my physiological and emotional awareness and personality for example. However, if I accept the results presented in this paper I have to accept the difference in definition of the ´I` and ´Me` thoughts according to the definition given by the psychologists. It is possible that the difference lies in that in some thoughts the particular brain areas are defined as being part of the DN whereas in other types of thought the same brain areas are regarded as essential for cognitive thought. For example, DN is known not to be involved in task orientated processing and therefore the thought ´I will go to the bank tomorrow` counts as forward planning and decision-making and value requiring known vPFC involvement according to cognitive functioning definition and ´Me` thought as defined here. Maybe here therefore, activity cannot be defined as part of the DN.

The authors did see however, a difference in neural response to heartbeats according to the content of thoughts at the time. The question must be asked therefore, what value would heart beat perception have to consciousness? To answer this question, we must look at the function of consciousness with reference to bodily awareness. In 1944, consciousness started out as a rare phenomenon associated with sudden super-alertness required in reacting to sudden emergencies (Claxten). Later on in 1977, Baars defined consciousness as a supremely functional adaptation and that, somewhere in our evolutionary past, consciousness would have saved us from danger. Therefore, an awareness of heartbeat in this case would be important. Consciousness also extended the ability of the brain to create transient states and McGovern and Baars linked cognitive functions to more higher order processing with definition and context setting, adaptation and learning. However, still important was consciousness`s role in error detection and awareness to things in memory for example. Therefore, heartbeat awareness and changes to it associated with biological learning and processing would be important. It would allow a quick response with less conscious thought then the other physiological body awareness, that of emotions.

The idea that awareness of heartbeat might be part of the conscious experience is clear if we consider that in a frightening situation people may feel their heart beating and explains the observations of the neural responses to heartbeats by the authors. This is supported by theories about the Self, Self-relatedness and Self-hood. In Baars Global Workplace Theory, the Default Network extends the realms of it. In this case, ´I` and ´Me` are used to distinguish between the Self-concept (includes values and beliefs about oneself) from the more fundamental Self-system (includes Self as the observer or agent). There is no conscious awareness of heartbeat. This theory led on to Damasio in 1999 defining the Self by distinguishing between the Proto-Self, the Core-Self, and the Autobiographical Self. The Proto-Self is described as a set of neural patterns which map the state of an organism moment by moment. In this case there is only unconscious awareness of the heartbeat and this is supported by other non-conscious bodily functions such as pupil dilation which have been in the past used to deduce attention. The basic kind of consciousness is the Core Self which is not dependent on memory, language or reasoning and provides the organism with a sense of Self in the present time. This is a transient entity ceaselessly re-created for each and every object with which the brain interacts. Memories form the third Damasio Self, the autographical self.

In 2003 and 2009 Metzinger established the representational view of Self by describing an inner tool called the Phenomenal Self-model (PSM). This is a distinct and coherent pattern of neural activity that allows the individual to integrate parts of the world into an inner image of him- or herself as a whole. Therefore, because of this Self model the individual can experience his own arms and legs as his own arms and legs, certain cognitive processes as his own thoughts and certain events in the motor parts of your brain as his own intentions and acts of will. In this case, the heartbeat and acknowledgment of the heartbeat would become part of the Phenomenal Self-model. A similar model, the concept of the Neural Subjective Frame has been proposed by Taillon-Baudry (one of the author`s of the article described here). This describes ´what I am` and is based on constantly updated neural maps of the internal state of the body. It constitutes a neural referential form from which the first person experience (the ´I` experience) can be created. Taillon-Baudry used this concept to form the basis of the investigation described here since the neural subjective form is rooted in the neural representation of visceral information which is transmitted through multiple anatomical pathways to a number of target sites, including posterior insula, ventral anterior cingulate cortex, amygdala and somatosensory cortex. In the experiments described here the conscious experience was linked to bodily function (that of heartbeats) and the the cortical processing associated with the signals from the cardiovascular system was studied by measuring the heart-evoked response (HER) using EEG. Co-variance of brain activity and heart rate was measured.

The problem with the theory is that the neural response to heartbeat is unconscious and thought is a conscious experience. Conscious perception to the heartbeat is not required. There is no conscious awareness of the heartbeat whilst the mind wanders and perhaps this is an example of the Self ´pampering` itself. It can think about things outside the normal routine functioning of the body which is carried on unconsciously. This is also observed with other signals such as pupil diameter.  Attention at this time is directed on higher thought processes and it is likely that according to Koch (2007) at the beginning there is a link between attention and consciousness, but later on they are highly or even entirely dissociated capabilities.  There is good evidence that attentional processes can operate without the attended stimuli ever reaching consciousness (Bressan, 2008) and this correlates to Franklin and Baars (2012) hypotheses about two types of unconscious process, one being preconscious and the other never-conscious. Distraction can impair the efficiency of unconscious processing. In mind wandering then there is no conscious awareness of heartbeats. Therefore, sensory and bodily information is processed in a wide variety of ways with different consequences depending on circumstances and cognitive involvement. Perception of the heartbeat can be trained and hence, the balance of unconscious and conscious processes can be adapted according to the wishes of the individual.

The other problem with the results of the experiments is the implications for the definition of a unified conscious experience. The binding problem of conscious experience appears to be intimately related to memory and attention. Crick and Koch investigated binding and consciousness and found 35-75 HZ oscillations (called gamma oscillations) or 40 Hz oscillations for groups of firing neurons. Crick suggested that these might be the neural correlates of visual awareness. It was argued that consciousness depends crucially on some form of rather short-term memory and also on some form of serial attentional mechanism and it was suggested that the thalamus controls attention by selecting the features to be bound together by synchronisation of firing. Crick suggested that consciousness only exists if certain cortical areas have reverberatory circuits (involving cortical layers 4 and 6) that project strongly enough to produce significant reverberations. Later in 2003, Crick and Koch changed their view saying that 40HZ oscillations were not a sufficient condition for the neural correlates of consciousness and instead argued that the primary role of synchronous firing was to assist one nascent firing coalition in its competition with others. The features of one single object or event are bound together when they form one part of one coalition and that coalition may involve neurons widely distributed over the brain. This view was supported by Taillon-Baudry. Zeki in 2007 extended this view with his Microconsciousness theory by saying that there is no single consciousness, but instead multiple consciousnesses (microconsciousnesses) distributed in time and space.

The problem with reference to these theories and the observations found in Babo-Rebelo, Richter and Taillon-Baudry`s study lies with the time difference described by Libet between neural firing (including those of the Global Workspace participating areas and neural responses to heartbeats) and conscious experience (Global Workspace thoughts occurring after the interruption). Libet produced his half-second delay theory where events become conscious only when the neurons involved in somatosensory cortex have been firing for a sufficient length of time (half a second). The majority of neural activity remains unconscious because it is too fleeting (needs at least 0.5 sec) or too unstable for neuronal adequacy. Paulignan also showed ´consciousness catch-up` when he  asked subjects to look back at where they thought a change had occurred and found that they reported the change much later than its actual occurrence, hence conscious awareness was too late for causal action. Therefore, in this case of neural responses and ´I` or ´Me` thinking, the heartbeat monitoring would occur in real-time, but the conscious thoughts according to Global Workspace Theory would be half a second slower. Therefore, the conscious thoughts are not related to the heartbeat responses recorded at that time, instead ones recorded half a second before. This supports the view of Marcel (1993) who looked at different reporting modalities such as blink and finger tap and found that they produced conflicting reports about the conscious experience. He argued ´slippage` in the unity of consciousness and therefore said opposing global interaction theories that there is no unified Self.

Therefore, although the experiments of Babo-Rebelo, Richter and Taillon-Baudry appear to suggest that neural responses to heartbeats are different in terms of brain area depending on what type of conscious thought is being processed at the time, the problem with time delay means that this is unlikely to be so clear-cut.

 Since we`re talking about the topic…………………….

………transient changes have also been reported in heart rate with perceptual decision-making. It was found that in the case of forewarned perceptual reaction-time tasks in response to warning stimuli, the heart followed a typical pattern of deceleration followed by an acceleration. Would this same pattern be followed if participants were asked instead to concentrate on  ´I`  or ´Me` thoughts?

…….it has been reported that looking into someone`s eyes for 10 minutes causes a feeling of being ´spaced out` as well as decreased colour intensity and sounds being louder than expected. What would happen to neural responses to heartbeats if the subject had to concentrate on only ´I` or ´Me` thoughts whilst looking into someone`s eyes for 10 minutes before being asked to report?

…..can we assume that if deep TMS is used and the experiment repeated that the activity would remain with the precuneus independent of experiment condition because deep TMS decreases self-awareness, and therefore only unconscious processing would occur?

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