Respiratory modulation of intensity ratings and psychomotor response times to acoustic startle stimuli

Effects of respiratory phases on the processing of emotional and non-emotional visual stimuli

The number of studies investigating the relationship between respiratory phases and cognitive/neural processing of external events has been increasing, but the findings remain controversial. This registered report examined the effect of the respiratory phase on the discrimination accuracy of visual stimuli in the emotional and non-emotional domains. Forty-two healthy young participants were asked to choose fearful over neutral facial expressions and to choose high-contrast over low-contrast Gabor patches during spontaneous nasal respiration. Event-related potentials (ERPs) were also recorded for each type of stimulus presented during each respiratory phase. It was hypothesized that discrimination accuracy would be higher when the stimuli were presented during inhalation than during exhalation. It was also hypothesized that the amplitudes of ERPs elicited by the stimuli would be greater during inhalation than during exhalation. For comparison, the effect of the cardiac phase was examined, with the expectation that discrimination accuracy would be higher when the stimuli were presented during systole than during diastole. It was also hypothesized that the amplitudes of ERPs elicited by the stimuli would be greater during systole than during diastole. As expected, the results indicated that fear discrimination accuracy was higher during inhalation than exhalation and during systole than diastole. However, this was not the case for contrast discrimination. No differences in ERPs were observed between respiratory phases in either task. These results suggest that natural breathing in through the nose facilitates the discrimination of emotional stimuli, possibly via subcortical processes.

-Cardiac cycle and respiration phase affect responses to the conditioned stimulus in young adults trained in trace eyeblink conditioning

Rhythms of breathing and heartbeat are linked to each other as well as to rhythms of the brain. Our recent studies suggest that presenting the conditioned stimulus during expiration or during the diastolic phase of the cardiac cycle facilitates neural processing of that stimulus and improves learning an eyeblink classical conditioning task. To date, it has not been examined whether utilizing information from both respiration and cardiac cycle phases simultaneously allows even more efficient modulation of learning. Here we studied whether the timing of the conditioned stimulus to different cardiorespiratory rhythm phase combinations affects learning trace eyeblink conditioning in healthy young adults. The results were consistent with previous reports: Timing the conditioned stimulus to diastole during expiration was more beneficial for learning than timing it to systole during inspiration. Cardiac cycle phase seemed to explain most of this variation in learning at the behavioral level. Brain evoked potentials (N1) elicited by the conditioned stimulus and recorded using electroencephalogram were larger when the conditioned stimulus was presented to diastole during expiration than when it was presented to systole during inspiration. Breathing phase explained the variation in the N1 amplitude. To conclude, our findings suggest that non-invasive monitoring of bodily rhythms combined with closed-loop control of stimulation can be used to promote learning in humans. The next step will be to test if performance can also be improved in humans with compromised cognitive ability, such as in older people with memory impairments.

Visual discrimination accuracy does not differ between nasal inhalation and exhalation when stimuli are voluntarily aligned to breathing phase

This study investigated the possible enhancement of visual discrimination accuracy by voluntarily adjusting the timing of stimulus presentation to a specific respiratory phase. Previous research has suggested that respiratory phases modulate perceptual and cognitive processing. For instance, a fearful face was identified faster when presented during nasal inhalation than during nasal exhalation, which could be related to changes in neural oscillatory activity synchronized with breathing in through one's nose. Based on such findings, the present study asked 40 young adults to perform an emotional discrimination task consisting of distinguishing fearful vs. neutral faces and a physical discrimination task consisting of distinguishing high- vs. low-contrast Gabor patches during nasal respiration. Participants presented themselves with the stimuli to be judged in a designated respiratory phase by pressing a button. It was hypothesized that fear discrimination accuracy would be higher during inhalation than exhalation if sensitivity to emotional stimuli increased during inhalation. Conversely, if overall visual sensitivity was enhanced during inhalation, the identical effect was expected for contrast discrimination. The results indicated that discrimination accuracy did not differ between inhalation and exhalation phases in either task. This result provided no evidence that the respiratory phase affected visual discrimination accuracy when people adjusted the timing of stimulus presentation to the onset of inhalation or exhalation.

Cardiac cycle phases affect auditory-evoked potentials, startle eye blink and pre-motor reaction times in response to acoustic startle stimuli

Startle stimuli evoke lower responses when presented during the early as compared to the late cardiac cycle phase, an effect that has been called 'cardiac modulation of startle' (CMS). The CMS effect may be associated with visceral-afferent neural traffic, as it is reduced in individuals with degeneration of afferent autonomic nerves. The aim of this study was to investigate whether the CMS effect is due a modulation of only early, automatic stages of stimulus processing by baro-afferent neural traffic, or if late stages are also affected. We, therefore, investigated early and late components of auditory-evoked potentials (AEPs) to acoustic startle stimuli (105, 100, 95 dB), which were presented during the early (R-wave +230 ms) or the late cardiac cycle phase (R +530 ms) in two studies. In Study 1, participants were requested to ignore (n = 25) or to respond to the stimuli with button-presses (n = 24). In Study 2 (n = 23), participants were asked to rate the intensity of the stimuli. We found lower EMG startle response magnitudes (both studies) and slower pre-motor reaction times in the early as compared to the late cardiac cycle phase (Study 1). We also observed lower N1 negativity (both studies), but higher P2 (Study 1) and P3 positivity (both studies) in response to stimuli presented in the early cardiac cycle phase. This AEP modulation pattern appears to be specific to the CMS effect, suggesting that early stages of startle stimulus processing are attenuated, whereas late stages are enhanced by baro-afferent neural traffic.