No abstract

Patients with right hemisphere lesions may be impaired in mobilizing attention and in emotional behavior. If so, autonomic responses to the mobilization of attention should be blunted. This was found when we studied the anticipatory heart rate deceleration that is seen normally in the foreperiod of a warned reaction task.

This study tested predictions from attentional, expectancy, and memory accounts of the Nc and early NSW components of ERPs in six-month-old infants. Visual stimuli were presented at the extremes of the probability continuum (a repeating stimulus versus novel stimuli) and at intermediate levels of probability (.80/.20 oddball task). Probability effects were found for Nc, early NSW, and visual fixation performance but there were no differences in the ERPs or behavior to familiar or novel stimuli. The results are discussed in terms of attentional and memory based interpretations of the Nc component.

This study recorded visual fixation performance and event-related brain potentials (ERPs) to examine processing of novel visual information in 6- to 7-mo.-old infants as well as to test attention- or memory-related hypotheses of the functional significance of the Nc-ERP component. Separate groups of infants were presented two versions of a novelty-probe task with three types of visual stimuli: (a) a frequent face on 70% of the trials, (b) an oddball face on 15% of the trials, and (c) novel probe stimuli on the remaining 15% of the trials. The novelty probes were faces in one group and irregular shapes in the second group. Analysis showed longer fixations and Nc responses of greater amplitude occurred to oddball and novel stimuli. It was concluded that Nc reflects a top-down, controlled processing mechanism that flexibly allocates attentional resources.

The purpose of the present study was to assess changes in heart period, heart‐period variance (HPV), and respiratory sinus arrhythmia (RSA) during manipulations of the baroreceptor reflex in anesthetized cats. Hypertension, induced via phenylephrine infusion, reflexly increases parasym‐pathetic activity and decreases sympathetic activity. Hypotension, produced by infusion of nitroprusside, leads to increased sympathetic activity and an inhibition of vagal influences on the heart. Specific autonomic contributions were assessed following administration of practolol, a β‐adrenergic blocker, or atropine methyl nitrate. Spectral analysis was used to quantify the component of HPV associated with respiration, i.e., RSA, which is proposed to be sensitive to vagal influences on the heart. The respiratory component of HPV is described by a statistic, V̂, which is the sum of the spectral densities of the heart period spectrum across the band of frequencies associated with normal respiration. Hypertension produced an increase in V̂ which was blocked by atropine infusion, but unaltered by beta‐adrenergic blockade. Hypotension decreased V̂ to near‐zero values which persisted after atropine and practolol infusion. These data suggest that V̂ is determined primarily by vagal factors. Correlations between V̂ and a previously used criterion measure of vagal tone further support this hypothesis. In contrast, heart period was sensitive to vagal and sympathetic factors. Heart period increases during hypertension were abolished with atropine and heart period decreases due to hypotension were eliminated by beta‐adrenergic blockade. These responses are consistent with the notion that heart period is under the control of both sympathetic and vagal factors. Since in an anesthetized preparation RSA is the major source of heart‐period variability, HPV responded similarly to V̂. The results suggest that the spectral estimate of RSA, V̂, is particularly sensitive to blood pressure induced reflexive changes in vagal efferent influences on the heart. It also appears that V̂ is less influenced by sympathetic factors than heart period, a commonly used estimate of vagal activity.

Changes in heart period (HP), heart-period variance (HPV), and the respiratory component of HPV in freely moving rats were examined following pharmacological manipulations known to influence vagal control of the heart. Spectral analysis was used to quantify the component of HPV associated with respiration which is proposed to be sensitive to vagal influences on the heart. The respiratory component of HPV is described by a statistic, V', which is the sum ofthe spectral densities ofthe heart period spectrum across the band of frequencies associated with normal respiration, Vagai tone was reflexively enhanced hy phenylephrine or peripherally blocked by atropine.Phenylephrine produced biphasic changes in HP and V, with the increases lasting from 0.5 to 2 hrs. Atropine resulted in significant decreases in HP, HPV and V. These decreases were immediate and sustained throughout the experiment, although there were signiflcant linear increases in HP and HPV from their initial post-injection values. In the saline condition, HP increased linearly across time.Results were discussed in terms of vagal and non-vagal control of the heart. It was suggested that, while all three variables are altered by manipulations of vagal influences on the heart, V seems to be influenced less by non-vagal control than HP and HPV.

Changes in heart period, heart period variance (HPV), and the respiratory component of HPV were examined during enhanced negative chronotropic influences on the heart produced by aortic depressor nerve (ADN) stimulation in urethane anesthetized rabbits. Spectral analysis was used to quantify the respiratory component of HPV, respiratory sinus arrhythmia (RSA). The statistic derived from spectral analysis which describes RSA, V̂, has been proposed to be sensitive to vagal influences on the heart. Stimulation of the ADN significantly increased V̂, heart period, and HPV. However, unlike V̂ and heart period, HPV values remained elevated following the end of stimulation. Propranolol administration did not alter the magnitude of the evoked increase in V̂, heart period, or HPV. In contrast, administration of atropine abolished the increases due to stimulation in all three measures. Heart period exhibited a monotonic relationship with stimulation current intensity. This relationship disappeared after propranolol administration suggesting sympathetic mediation. The results suggest that V̂ is sensitive to manipulations of vagal influences on the heart. In addition, V̂ often responds in a different manner from heart period and HPV.

This study tested theoretical accounts of the Nc component of the event-related brain potentials in six-month-old infants by replicating and extending a previous study [Ackles, P. K., & Cook, K. G. (2007). Attention or memory? Effects of familiarity and novelty on the Nc component in event-related brain potentials in six-month-old infants. The International Journal of Neuroscience, 117, 837-867]. Stimulus familiarity and novelty of visual stimuli were manipulated within and across four groups of infants to test predictions from attentional, memory, and expectancy accounts of Nc. Nc amplitudes were the larger to oddball stimuli in the. 80/.20 oddball group and One Face group than to frequent stimuli in oddball group and to novel stimuli in the Novel Faces and Novel Pictures groups. The results supported an attention-based interpretation of Nc.