Baroreceptor activity impacts upon controlled but not automatic distractor processing

Rhythmic firing of neurons in the medulla of conscious freely behaving rats: rhythmic coupling with baroreceptor input

Recent investigations emphasized the importance of neural control of cardiovascular adjustments in complex behaviors, including stress, exercise, arousal, sleep-wake states, and different tasks. Baroreceptor feedback is an essential component of this system acting on different time scales from maintaining stable levels of cardiovascular parameters on the long-term to rapid alterations according to behavior. The baroreceptor input is essentially rhythmic, reflecting periodic fluctuations in arterial blood pressure. Cardiac rhythm is a prominent feature of the autonomic control system, present on different levels, including neuron activity in central circuits. The mechanism of rhythmic entrainment of neuron firing by the baroreceptor input was studied in great detail under anesthesia, but recordings of sympathetic-related neuron firing in freely moving animals remain extremely scarce. In this study, we recorded multiple single neuron activity in the reticular formation of the medulla in freely moving rats during natural behavior. Neurons firing in synchrony with the cardiac rhythm were detected in each experiment (n = 4). In agreement with prior observations in anesthetized cats, we found that neurons in this area exhibited high neuron-to-neuron variability and temporal flexibility in their coupling to cardiac rhythm in freely moving rats, as well. This included firing in bursts at multiples of cardiac cycles, but not directly coupled to the heartbeat, supporting the concept of baroreceptor input entraining intrinsic neural oscillations rather than imposing a rhythm of solely external origin on these networks. It may also point to a mechanism of maintaining the basic characteristics of sympathetic neuron activity, i.e., burst discharge and cardiac-related rhythmicity, on the background of behavior-related adjustments in their firing rate.

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.

Does the body give the brain an attentional boost? Examining the relationship between attentional and cardiac gating

Studies on mind-body interactions have largely focused on how mental states modulate bodily physiological responses. Increasing evidence suggests that bodily states also modulate mental states. Here we investigated how both may be integrated in the brain at the resolution of a heartbeat, examining how phasic fluctuations of peripheral blood pressure and central attentional resources combine to influence cognition. We examined the effects of cardiac phase on the performance of two simultaneous tasks: a go/no-go letter detection task where targets were concurrently presented on background faces and a short-term memory face discrimination task. Short-term memory for the background face was better when the initial face was encoded during the systole rather than diastole phase and when it was paired with a target rather than a distractor. There was no significant interaction between cardiac phase and letter detection. These data suggest that peripheral blood pressure and central attention independently regulate cognitive performance.

The Effect of Physical Resistance Training on Baroreflex Sensitivity of Hypertensive Rats

Background:

Baroreceptors act as regulators of blood pressure (BP); however, its sensitivity is impaired in hypertensive patients. Among the recommendations for BP reduction, exercise training has become an important adjuvant therapy in this population. However, there are many doubts about the effects of resistance exercise training in this population.

Objective:

To evaluate the effect of resistance exercise training on BP and baroreceptor sensitivity in spontaneously hypertensive rats (SHR).

Method:

Rats SHR (n = 16) and Wistar (n = 16) at 8 weeks of age, at the beginning of the experiment, were randomly divided into 4 groups: sedentary control (CS, n = 8); trained control (CT, n = 8); sedentary SHR (HS, n = 8) and trained SHR (HT, n = 8). Resistance exercise training was performed in a stairmaster-type equipment (1.1 × 0.18 m, 2 cm between the steps, 80° incline) with weights attached to their tails, (5 days/week, 8 weeks). Baroreceptor reflex control of heart rate (HR) was tested by loading/unloading of baroreceptors with phenylephrine and sodium nitroprusside.

Results:

Resistance exercise training increased the soleus muscle mass in SHR when compared to HS (HS 0.027 ± 0.002 g/mm and HT 0.056 ± 0.003 g/mm). Resistance exercise training did not alter BP. On the other hand, in relation to baroreflex sensitivity, bradycardic response was improved in the TH group when compared to HS (HS -1.3 ± 0.1 bpm/mmHg and HT -2.6 ± 0.2 bpm/mmHg) although tachycardia response was not altered by resistance exercise (CS -3.3 ± 0.2 bpm/mmHg, CT -3.3 ± 0.1 bpm/mmHg, HS -1.47 ± 0.06 bpm/mmHg and HT -1.6 ± 0.1 bpm/mmHg).

Conclusion:

Resistance exercise training was able to promote improvements on baroreflex sensitivity of SHR rats, through the improvement of bradycardic response, despite not having reduced BP.

Cardiac afferent activity modulates the expression of racial stereotypes

Negative racial stereotypes tend to associate Black people with threat. This often leads to the misidentification of harmless objects as weapons held by a Black individual. Yet, little is known about how bodily states impact the expression of racial stereotyping. By tapping into the phasic activation of arterial baroreceptors, known to be associated with changes in the neural processing of fearful stimuli, we show activation of race-threat stereotypes synchronized with the cardiovascular cycle. Across two established tasks, stimuli depicting Black or White individuals were presented to coincide with either the cardiac systole or diastole. Results show increased race-driven misidentification of weapons during systole, when baroreceptor afferent firing is maximal, relative to diastole. Importantly, a third study examining the positive Black-athletic stereotypical association fails to demonstrate similar modulations by cardiac cycle. We identify a body–brain interaction wherein interoceptive cues can modulate threat appraisal and racially biased behaviour in context-dependent ways.

Black individuals are racially stereotyped as threatening but how bodily signals may affect these misperceptions is not known. Here Azevedo and colleagues show that these race-driven responses are affected by the cardiac cycle, being more biased when arterial baroreceptor activation is maximal.