Healthcare (Commonwealth Union) – A study funded by the Swiss National Science Foundation (SNSF) has uncovered previously unknown connections between the body and brain. Research from the University of Fribourg reveals how our bodily rhythms influence visual perception.
Taking a deep breath for clarity might be more effective than expected. Breathing has a direct physiological effect on how we perceive visual stimuli. This is the conclusion of Juliane Britz, a psychologist and neuroscientist at the University of Fribourg. Her experiment demonstrated that heart and breathing rhythms affect how we become aware of visual stimuli. The findings, supported by the SNSF, were recently published in PNAS.
In this study, participants watched a screen where grey squares with diagonal crosshatching appeared briefly. After each visual cue, they were asked two questions: Did they see the pattern, and what was its orientation? The contrast was adjusted so they only consciously saw it 50% of the time. Yet, even when they didn’t consciously perceive the pattern, they correctly identified its orientation 85% of the time. This suggests that, even without conscious awareness, participants processed the visual information, relying on intuition to make accurate decisions.
During the experiment, electrodes were used to record the electrical activity in participants’ brains (via electroencephalogram, EEG) and hearts (via electrocardiogram, ECG). A belt around the abdomen also monitored their breathing by measuring abdominal volume. By comparing the brain’s electrical signals between instances where subjects were shown crosshatching and where they were not, the psychologist could identify “neuronal markers of consciousness.”
The team then examined how these neural markers changed depending on the cardiac cycle. Their analysis revealed that when the image was shown during a relaxed phase of the heart, the markers of consciousness appeared approximately 150 milliseconds earlier than when the heart was contracting. Breathing had a similar effect on visual perception, with the same delay occurring when the image appeared during exhalation rather than inhalation.
Juliane Britz pointed out that the influence of bodily rhythms on the brain is controlled by pressure receptors in the arteries. The researchers further indicated that these receptors remain inactive when the heart is relaxed or during inhalation but become active when the heart contracts or during exhalation. This activation triggers a sort of neural traffic jam, slowing down the brain’s processing of visual information.
The discovery has revealed that the brain processes visual information through two different pathways depending on whether bodily signals are present or not. Previously, it was known that visual information first reaches the visual cortex before passing through other regions of the brain to reach the point of conscious awareness. The new findings show that at the end of this pathway, visual information can take one of two routes. If bodily signals are present, it passes through the parietal cortex, while in their absence, it passes through the neighboring frontal cortex. This discovery provides a new explanation for the long-standing debate between researchers who believed that consciousness emerges in the frontal cortex and those who thought it originated in the parietal cortex. The researcher stated that it’s as if there are two possible modes of activation for a visual stimulus, depending on whether there are signals coming from the body or not. Ultimately, it is the cardiac and respiratory rhythms that determine, through pressure receptors in the arteries, which cerebral pathway visual perception will take. Juliane Britz stressed the point that on the fundamental nature of the study and would rather not make any assumptions about the reason bodily cycles play a role in the neural markers of consciousness. “These results resolve the controversy surrounding the neurophysiological markers of awareness and the area of the brain in which they occur.” And for her, the main takeaway is simple: we need to be less ‘brain-centred’ in neuroscience. “Bodily signals, which are often discarded and considered as noise, should no longer be dismissed in this way. The brain is not independent from the body.”
