When the heart inhibits the brain: Cardiac phases modulate short-interval intracortical inhibition

The phasic cardiovascular activity influences the central nervous system through the systolic baroreceptor inputs, inducing widespread inhibitory effects on behavior. Through transcranial magnetic stimulation (TMS) delivered during resting-state over the left primary motor cortex and across the different cardiac phases, we measured corticospinal excitability (CSE) and distinct indices of intracortical motor inhibition: short (SICI) and long (LICI) interval, corresponding to GABAA and GABAB neurotransmission, respectively. We found a significant effect of the cardiac phase on short-intracortical inhibition, without any influence on LICI. Specifically, SICI was stronger at systole compared to diastole. These results show a tight relationship between the cardiac cycle and the inhibitory neurotransmission within M1, and in particular with GABAA-ergic-mediated motor inhibition. We hypothesize that this process requires greater motor control via the gating mechanism and that this, in turn, needs to be recalibrated through the modulation of intracortical inhibition.

Body as First Teacher: The Role of Rhythmic Visceral Dynamics in Early Cognitive Development

Embodied cognition-the idea that mental states and processes should be understood in relation to one's bodily constitution and interactions with the world-remains a controversial topic within cognitive science. Recently, however, increasing interest in predictive processing theories among proponents and critics of embodiment alike has raised hopes of a reconciliation. This article sets out to appraise the unificatory potential of predictive processing, focusing in particular on embodied formulations of active inference. Our analysis suggests that most active-inference accounts invoke weak, potentially trivial conceptions of embodiment; those making stronger claims do so independently of the theoretical commitments of the active-inference framework. We argue that a more compelling version of embodied active inference can be motivated by adopting a diachronic perspective on the way rhythmic physiological activity shapes neural development in utero. According to this visceral afferent training hypothesis, early-emerging physiological processes are essential not only for supporting the biophysical development of neural structures but also for configuring the cognitive architecture those structures entail. Focusing in particular on the cardiovascular system, we propose three candidate mechanisms through which visceral afferent training might operate: (a) activity-dependent neuronal development, (b) periodic signal modeling, and (c) oscillatory network coordination.

Disentangling sensorimotor and cognitive cardioafferent effects: A cardiac-cycle-time study on spatial stimulus-response compatibility

Cardiac-cycle-time effects are attributed to variations in baroreceptor (BR) activity and have been shown to impinge on subcortical as well as cortical processes. However, cognitive and sensorimotor processes mediating voluntary responses seem to be differentially affected. We sought to disentangle cardiac-cycle-time effects on subcortical and cortical levels as well as sensorimotor and cognitive processes within a spatial stimulus-response-compatibility paradigm employing startling stimuli of different modalities. Air-puffs and white noise-bursts were presented unilaterally during either cardiac systole or diastole while bilateral startle EMG responses were recorded. Modality, laterality and cardiac-cycle-time were randomly varied within-subjects. Cognitive and sensorimotor stimulus-response-compatibility was orthogonally varied between-subjects: Participants (N = 80) responded to the stimuli via left/right button-push made with either the contra- or ipsilateral hand (sensorimotor compatibility) on either the ipsi- or contralateral button (cognitive compatibility). We found that sensorimotor compatible reactions were speeded during systole whereas sensorimotor incompatible ones were prolonged. This effect was independent of cognitive compatibility and restricted to auditory stimuli. Startle was inhibited during systole irrespective of modality or compatibility. Our results demonstrate how differential cardiac-cycle-time effects influence performance in conflict tasks and further suggest that stimulus-response-compatibility paradigms offer a viable method to uncover the complex interactions underlying behavioral BR effects.

The heart of cognitive control: Cardiac phase modulates processing speed and inhibition

Bodily states are heavily intertwined with cognitive processes. A prominent communication channel between bodily signals and brain structures is provided by baroreceptors. Their phasic activity associated with the cardiac phase has been shown to modulate cognitive control in socio-emotional contexts. However, whether this effect is specific to the affective dimension or impacts general cognitive control processes remains controversial. The aim of the present study is to investigate the effect of cardiac phase on different facets of cognitive control. We built a nonemotional cognitive control task to delineate mechanisms such as processing speed, response selection, response inhibition, and conflict monitoring. We showed that the systole (after the blood is ejected from the heart), compared to the diastole, was related to faster responses. Moreover, the cardiac phase dynamics also impacted response inhibition, with an increased probability of failure toward the middle of the course of systole. Although the reported effects were small in terms of magnitude, they highlight the influence of bodily states on abstract cognitive processes.

Baroreceptor activity impacts upon controlled but not automatic distractor processing

Changes within the cardiovascular system have been shown to alter sensorimotor and memory performance, pain perception as well as cortical arousal. This influence is assumed to be mediated by afferent feedback of baroreceptors that when stimulated exert inhibitory effects on cortical structures. Mainly responsible for short-term regulation of blood pressure, afferents of the baroreceptors are widely connected to subcortical and cortical structures like the insular cortex. A putative impact on cognitive control processes remains an open question, however. Using a sequential distractor priming task, the present study investigated whether inhibitory influences of baroreceptor activation apply to selective information processing in the presence of irrelevant information. In particular, we assessed distractor-response binding and Negative Priming as indices of automatic and controlled distractor processing, respectively. Baroreceptor activation was experimentally manipulated by the systematic variation of body position. The results showed that only Negative Priming but not distractor-response binding was modulated by body position suggesting that controlled but not automatic processing of distractors is affected by baroreceptor activity.

The neural subjective frame: from bodily signals to perceptual consciousness

The report 'I saw the stimulus' operationally defines visual consciousness, but where does the 'I' come from? To account for the subjective dimension of perceptual experience, we introduce the concept of the neural subjective frame. The neural subjective frame would be based on the constantly updated neural maps of the internal state of the body and constitute a neural referential from which first person experience can be created. We propose to root the neural subjective frame 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. We review existing experimental evidence showing that the processing of external stimuli can interact with visceral function. The neural subjective frame is a low-level building block of subjective experience which is not explicitly experienced by itself which is necessary but not sufficient for perceptual experience. It could also underlie other types of subjective experiences such as self-consciousness and emotional feelings. Because the neural subjective frame is tightly linked to homeostatic regulations involved in vigilance, it could also make a link between state and content consciousness.

The behavioral impact of baroreflex function: a review

The baroreflex consists of a negative feedback loop adjusting heart activity to blood pressure fluctuations. This review is concerned with interactions between baroreflex function and behavior. In addition to changes in baroreflex cardiac control subject to behavioral manipulations, interindividual differences in reflex function predicted psychological and central nervous features. The sensitivity of the reflex was inversely related to cognitive performance, evoked potential amplitudes, experimental pain sensitivity, and the severity of clinical pain. Possible variables moderating the strength of the associations are tonic blood pressure, gender, and psychiatric disease. It is suggested that these observations reflect inhibition of higher brain function by baroreceptor afferents. While in many cases increased baroreflex function implies stronger inhibition, individual and situational factors modulate the behavioral impact of cardiac regulation.

Tonic blood pressure modulates the relationship between baroreceptor cardiac reflex sensitivity and cognitive performance

This study explored the effects of tonic blood pressure on the association between baroreceptor cardiac reflex sensitivity and cognitive performance. Sixty female participants completed a mental arithmetic task. Baroreceptor reflex sensitivity was assessed using sequence analysis. An interaction was found, indicating that the relationship between baroreceptor reflex sensitivity and cognitive performance is modulated by blood pressure levels. Reflex sensitivity was inversely associated to performance indices in the subgroup of participants with systolic blood pressure above the mean, whereas the association was positive in participants with systolic values below the mean. These results are in accordance with the findings in the field of pain perception and suggest that tonic blood pressure modulates the inhibitory effects of baroreceptor stimulation on high central nervous functions.

Cardiac modulation of startle eye blink

As an alternative to interoceptive paradigms that depend on the participants' active cooperation, two studies are presented to show that startle methodology may be employed to study visceral afferent processing. The first study of 38 volunteers showed that startle responses were smaller when elicited during cardiac systole as compared to diastole. In the second study, 31 diabetic patients were divided into two groups, having normal or diminished (<6 ms/mmHg) baroreflex sensitivity (BRS). Patients with normal BRS showed the same results found in healthy volunteers. Diabetic patients with diminished BRS did not show this pattern. Because diminished BRS is an indicator of impaired baro-afferent signal transmission, it is concluded that cardiac modulation of startle is associated with intact baro-afferent feedback. Thus, pre-attentive startle methodology is feasible to study visceral afferent processing originating from the cardiovascular system.

Effects of arterial and cardiopulmonary baroreceptor activation on simple and choice reaction times

Variations in simple reaction time over the cardiac cycle could be due to cortical inhibition associated with activation of the arterial baroreceptors. It has been proposed that higher order cognitive processing may also be modulated and, moreover, that cardiopulmonary baroreceptors may have similar inhibitory effects. This study examined arterial and cardiopulmonary baroreceptor effects on simple and choice reaction times by presenting visual stimuli at one of six intervals after the R-wave of the electrocardiogram (0, 150, 300, 450, 600, 750 ms) while participants lay supine with their legs raised or lowered. Reaction times were slower early in the cardiac cycle compared to later whereas reaction time slopes were not different. No cardiopulmonary baroreceptor effects were found. Cardiac cycle effects on reaction time are consistent with the arterial baroreceptor hypothesis and appear to be confined to lower order sensory-motor processing.

Psychomotor speed in hypertension: Effects of reaction time components, stimulus modality, and phase of the cardiac cycle

Hypertension is characterized by cognitive deficits. As evidence for impaired psychomotor speed, including slower reaction times, is mixed, we aimed to provide a detailed investigation of simple reaction time in hypertension. Pre-motor and motor reaction times were measured across the cardiac cycle in 30 hypertensives and 29 normotensives to determine the effects of phasic and tonic blood pressure on performance. Auditory, visual, and tactile simple reaction time tasks were completed with stimuli presented 0, 300, and 600 ms after the R-wave of the electrocardiogram. Reaction times did not differ between hypertensives and normotensives. Although pre-motor reaction times were faster during the late phase than the early phase of the cardiac cycle whereas motor reaction times were unchanged, this effect was similar for hypertensives and normotensives. No sensory-motor deficits were evident in these hypertensives regardless of baroreceptor activity.