The history of the cognitive sciences can lead us to think that, throughout the centuries, there has been a battle between the heart and the brain to occupy the only throne in the seat of the mind. However, modern science these days is showing a landscape which is much more open, complex and democratic, where the brain and the heart can interact in that which we call mind.
Although studies up to the present day are very promising, it seems cognitive neuroscience will experience a change in paradigm that will go from cerebral centrism to an idea of embodied mind. A few months ago, the publisher of the prestigious scientific journal “Nature” wrote in his editorial “Complex illnesses become complicated”, echoing the studies that show the influence of different organs on the body in purely cognitive pathologies. If there is an organ that popular wisdom bestowed intelligence on is the heart, and it seems modern science is demonstrating it. These hunches that we have all felt and guided our decisions or perceptions of the outside world are translated into electrical interactions between the head and the heart. Science insinuates that reality manifests itself according to this dialogue between the head and the heart.
In the year 2009, Gray and collaborators (Gray, Rylander, Harrison, Wallin, & Critchley, 2009) observed that the value of the intensity of a painful stimulus applied on the skin of the participants depended on whether the said stimulus was in phase with cardiac discharge (systole) or it was applied randomly in relation to the heartbeat. The cardiac variability of the subjects correlated with the haemodynamic activity in cerebral zones like the insula and the amygdala, both related with processing emotions. According to the authors, the processing of the stimuli depends on the autonomous cardiovascular system underlying the subjective experience of the stimuli. In the year 2014, the group led by Catherine Tallon-Baudry (Park, Correia, Ducorps, & Tallon-Baudry, 2014), (Babo-Rebelo, Richter, & Tallon-Baudry, 2016), demonstrated that the perception of a neutral visual stimulus (only a dot on a screen) depended on a cerebral response of the cardiac pulse in frontal areas, parietal and cingulate cortex, in a way that the lack of brain response evoked by the cardiac pulse supposed the loss of perception of the said stimulus. In other words, we see something so simple as a dot on the screen if our heart and brain communicate coherently. Very recently an experiment was carried out to see the unconscious causes of racist bias (Azevedo, Garfinkel, Critchley, & Tsakiris, 2017). The participants of the study saw images of men from black and white races with different instruments in their hands, some neutral (telephones or tools) and others dangerous (firearms or knives). On asking about the type of instruments that has been observed in the images, a bias was seen, attributing dangerous items to people of black race. The radical discovery of the studio was that the racist bias depended on whether the images had been shown during the cardiac pulse or some time later. This study shows us that the subjective experience of the participants in judging the images depended on whether it was processed in the heart.
What do mind sciences, especially neuroscience, assume that the heart is part of the cognitive system? From the point of view of the philosophy of the mind, the door is opened to the study of the embodied mind. The development of this branch has been, until now mainly theoretical. The models of the mind proposed by Merlau Ponty, William James, or Francisco Varela among others, can find a base or complement in physiological models developed from measures of the cerebral and cardiac dynamic and could provide the essential base for the comprehension of the mind as a holomic system, a system that needs the cooperation of the whole body. The revolution has not only arrived to the heart; things are more complex. In the last five years some scientific articles have appeared, which support a change of paradigm in cognitive neuroscience, changing from cerebral centrism to a embodied mind context. These studies highlight the influence of the respiratory system (Duffin,2016), digestive system (Cryan and Dinan,2012) and cardiovascular system (Critchley, Wiens, Rotshtein, Öhman, & Dolan, 2004) in the brain dynamics. A great change is upcoming. “We are body” could be the motto of new cognitive science.
The clinical implications of considering the heart as inseparable to the brain are at the moment unforeseen. For example, for many years, the clinical evidence strongly connected dementia with cardiovascular illnesses. A study calculated that the reduction of at least 5 factors of cardiovascular risk could avoid 7 million cases of dementia in the USA (Qiu & Fratiglioni, 2015). Another study showed us that to do physical exercise a few hours after studying, which implies an increase in the heart rate, improves consolidation of memory (Cropley et al., 2017). Somehow the cardiac dynamic affects the neurons of the hippocampus, the main cerebral station of memory. Should therapies based on physical exercise or corporal perception be included or enhanced to avoid illnesses and improve our cognitive output?
There is a field in neuroscience where the influence of the body on the brain can and must throw everything upside down: the spontaneous oscillations of the brain. In other words, why is the brain so active when we do not do anything? When talked about the basal dynamic of the brain (as it is called when we do nothing), people often question their interest. However, it is one of the fields of greater transdency in neuroscience. To start, it is the reference used to indicate if the area of the brain has “increased” its activity when we carry out a cogntive task. Increased with regards to this basal state. Thus, the base from which our neurons starts determines the performance of a task, makes us predisposed to be more responsive to it or, in contrast, to be slower.
Our brain is a quite inertial system. It needs time and motivation to modulate its activity. This basal state reflects many cognitive and psychiatric alterations. It is one of the first evidences of Alzheimer´s, schizophrenia or brain damage, and therefore has great predictive value in the evolution of such disorders. Until now, this basal state has been called the “spontaneous state” of the brain and we have arrived to say that it is described as a stochastic or random dynamic (Cabral, Kringelbach, & Deco, 2017). However, from here we postulate that this that we call spontaneity is no more than not knowing the sources that produce this influence to the brain, like the heart and the rest of the body.
From the scientific point of view, we have just open up a new field and there is much work to be done. It is not known which paths or electrical mechanisms measure the relationship between the heart and the brain, nor the implications that this will have for the clinic or for the social awareness. It is not known what organs have most influence on the brain or if it is necessary to speak of influences of one on another, where there is the implication of a hierarchy, but that the mind could need all the body to manifest itself.
Azevedo, R. T., Garfinkel, S. N., Critchley, H. D., & Tsakiris, M. (2017, January 17). Cardiac afferent activity modulates the expression of racial stereotypes. Nature Communications. Springer Nature. Retrieved from http://dx.doi.org/10.1038/ncomms13854
Babo-Rebelo, M., Richter, C. G., & Tallon-Baudry, C. (2016, July 27). Neural Responses to Heartbeats in the Default Network Encode the Self in Spontaneous Thoughts. The Journal of Neuroscience. Society for Neuroscience. Retrieved from http://dx.doi.org/10.1523/jneurosci.0262-16.2016
Cabral, J., Kringelbach, M. L., & Deco, G. (2017, March). Functional connectivity dynamically evolves on multiple time-scales over a static structural connectome: Models and mechanisms. NeuroImage. Elsevier BV. Retrieved from http://dx.doi.org/10.1016/j.neuroimage.2017.03.045
Critchley, H. D., Wiens, S., Rotshtein, P., Öhman, A., & Dolan, R. J. (2004, January 18). Neural systems supporting interoceptive awareness. Nature Neuroscience. Springer Nature. Retrieved from http://dx.doi.org/10.1038/nn1176
Cropley, M., Plans, D., Morelli, D., Sütterlin, S., Inceoglu, I., Thomas, G., & Chu, C. (2017, January 31). The Association between Work-Related Rumination and Heart Rate Variability: A Field Study. Frontiers in Human Neuroscience. Frontiers Media SA. Retrieved from http://dx.doi.org/10.3389/fnhum.2017.00027
Cryan, J. F., & Dinan, T. G. (2012, September 12). Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nature Reviews Neuroscience. Springer Nature. Retrieved from http://dx.doi.org/10.1038/nrn3346
Duffin, J. (2016, October 21). Faculty of 1000 evaluation for Arterial CO2 Fluctuations Modulate Neuronal Rhythmicity: Implications for MEG and fMRI Studies of Resting-State Networks. F1000 – Post-publication peer review of the biomedical literature. Faculty of 1000, Ltd. Retrieved from http://dx.doi.org/10.3410/f.726643886.793524555
Gray, M. A., Rylander, K., Harrison, N. A., Wallin, B. G., & Critchley, H. D. (2009, February 11). Following One’s Heart: Cardiac Rhythms Gate Central Initiation of Sympathetic Reflexes. Journal of Neuroscience. Society for Neuroscience. Retrieved from http://dx.doi.org/10.1523/jneurosci.3363-08.2009
Park, H.-D., Correia, S., Ducorps, A., & Tallon-Baudry, C. (2014, March 9). Spontaneous fluctuations in neural responses to heartbeats predict visual detection. Nature Neuroscience. Springer Nature. Retrieved from http://dx.doi.org/10.1038/nn.3671
Qiu, C., & Fratiglioni, L. (2015, January 13). A major role for cardiovascular burden in age-related cognitive decline. Nature Reviews Cardiology. Springer Nature. Retrieved from http://dx.doi.org/10.1038/nrcardio.2014.223