Cardiac activity: its role in perception and action

Patterns of cardiac activity continuously vary with environmental
demands, accelerating or decelerating depending on circumstances. Simultaneously, cardiac cycle affects a host of higher-order processes, where systolic baroreceptor activation largely impairs processing. However, a unified functional perspective on the role of cardiac signal in perception and action has been lacking.

— Patterns of cardiac activity continuously vary with environmental demands.
— At the same time, baroreceptor activity on every heartbeat affects perception and action.
— Cardiac deceleration and acceleration adaptively regulate the level of baroreceptor signal through gain modulation.
— Dynamic heart rate adjustments thus allow to dynamically regulate precision assigned to external versus internal evidence.
— This allows for optimisation of perception and action.

The analysis of existing strands of literature shows that deceleration is an adaptive mechanism dynamically attenuating the baroreceptor signal associated with each heartbeat to minimise its impact on exteroceptive processing. This mechanism allows to enhance attention afforded to external signal and prepare an appropriate course of action.
Conversely, acceleration is associated with a reduced need to attend externally, enhanced action tendencies and behavioural readjustment.
This novel account demonstrates that dynamic adjustments in heart rate serve the purpose of regulating the level of precision afforded to internal versus external evidence in order to optimise perception and action. This highlights that the importance of cardiac signal in adaptive behaviour lies in its dynamic regulation.

Two examples of precision weighting.
In both diagrams, sensory evidence from interoceptive and exteroceptive signals is combined to form a percept of the situation faced by the organism and determine action tendencies (priors are omitted for simplicity).
(1) In the upper diagram, the interoceptive signal is afforded a high level of precision, and thus exerts a greater influence than the exteroceptive signal on the resulting percept. An example could be where, in a state of high arousal, one perceives an ambiguous sound as a thief breaking in through the downstairs window, rather than a more likely and less emotionally-weighted scenario, such as the wind moving the window panes.
(2) In the lower diagram, the signals are weighted equally and thus exert the same influence. Here, through lowering the interoceptive precision, the percept is steered back towards the exteroceptive channel and further information gathering. Note that the mean of each distribution remains the same in both diagrams: the only change is to the precision, but the percept shifts as a result.
Illustration of the proposed mechanism for the functional role of cardiac signal in adaptive perception and action. To satisfy perception/attention to the external world, such as in cases of threat-, anticipation-, and error-related deceleration, the parasympathetic brake is applied to dynamically slow down the heart rate, thus reducing the frequency of noise-inducing events (baroreceptor activity upon each heartbeat). This allows the brain to set the precision level appropriately, reducing the impact of interoceptive signalling on perception. As such, enhanced precision of exteroceptive evidence is what underlies the instances of enhanced perception reviewed in text.
Conversely, when the perceive/attend imperative is satisfied and it is time to act, the parasympathetic brake is removed to restore or accelerate the heart rate to furnish action demands. Importantly, the precision modulations are not fully symmetrical – interoceptive signal is not automatically prioritised for action to shape the percept, but rather restored to default for accurate and timely action and allostatic control.

The picture emerging from this analysis is that the importance of cardiac signal in adaptive behaviours lies not in the signal itself, but rather in its dynamic regulation. Cardiac deceleration is a reflection of a centrally-driven mechanism geared at reducing the influence of internal signal affecting external processing when efficient exteroception is paramount. This is likely to occur through dynamic and selective modulations in neuronal excitability. We propose that this is achieved in order to adaptively control the level of precision attached to external versus internal information on the principles of precision-weighing
under Bayesian inference.

This perspective can provide insight into the general functional involvement of bodily signals in adaptive behaviour, and may be applied to other types of rhythmic bodily activity. Incoming evidence in the domain of respiration shows that perceptual and active processes may be similarly tuned to the respiratory stages of inspiration and expiration, with stronger respiratory phase-locking related to better somatosensory detection performance and motion tracking, as well as more frequent action initiation during expiration. Another candidate are gastric waves. While respiration is known to be (to some extent) coupled with the heart, gastric waves vary based on the current state of the stomach, so it is conceivable that their effects could vary in a similar fashion, i.e. through up- or down-regulation in line with context.

The framework can also provide insights into phenomena characterised by a reduction in perceptual or behavioural performance, such as inattentional blindness/deafness (failure to perceive an unexpected stimulus when attention is engaged elsewhere), mind-wandering (decoupling of attention from processing external or relevant information), or maladaptive perseveration (continuing a response after original stimulation ceases, rendering it irrelevant to the stimulus). In line with the theoretical predictions, those phenomena show an opposing pattern of cardiac activity, with elevated heart rate, as well as heightened alpha power, linked to an impairment in perceptual efficacy or adaptation.

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