Enrica Laura Santarcangelo

Deriving the respiratory sinus arrhythmia from the heartbeat time series using Empirical mode decomposition

Abstract Heart rate variability (HRV) is a well-known phenomenon whose characteristics are of great clinical relevance in pathophysiologic investigations. In particular, respiration is a powerful modulator of HRV contributing to the oscillations at highest frequency. Like almost all natural phenomena, HRV is the result of many nonlinearly interacting processes; therefore any linear analysis has the potential risk of underestimating, or even missing, a great amount of information content. Recently the technique of empirical mode decomposition (EMD) has been proposed as a new tool for the analysis of nonlinear and nonstationary data. We applied EMD analysis to decompose the heartbeat intervals series, derived from one electrocardiographic (ECG) signal of 13 subjects, into their components in order to identify the modes associated with breathing. After each decomposition the mode showing the highest frequency and the corresponding respiratory signal were Hilbert transformed and the instantaneous phases extracted were then compared. The results obtained indicate a synchronization of order 1:1 between the two series proving the existence of phase and frequency coupling between the component associated with breathing and the respiratory signal itself in all subjects.

Modulation of pain-induced endothelial dysfunction by hypnotisability.

&NA; Mental stress induces endothelial dysfunction, that is a reduction of the post‐occlusion brachial artery flow‐mediated vasodilation (FMD). This does not occur in subjects highly susceptible to hypnosis (Highs) in either the waking or hypnotic state. The aim of the present experiment was to assess whether endothelial dysfunction is also induced by acute nociceptive stimulation and whether high hypnotisability and/or the specific instruction of analgesia prevent its occurrence in awake highly hypnotizable individuals. Thus, nine Highs and nine subjects with low susceptibility to hypnosis (Lows) underwent an experimental session including the administration of pressor pain and of pressor pain associated with the instruction of analgesia. Heart rate, basal artery diameters and brachial artery flow‐mediated vasodilation were measured during stimulation and rest conditions. Heart rate exhibited slight changes not modulated by hypnotisability. During painful stimulation both Highs and Lows showed a decrease of FMD, but it was significantly less pronounced in Highs. During the administration of painful stimulation together with the instruction of analgesia, only Highs reported analgesia and their FMD no longer decreased. This study provides the first evidence of pain‐related endothelial dysfunction and extends previous findings concerning a sort of natural protection of Highs against the vascular effects of mental stress to acute pain.

Autonomic and EEG correlates of emotional imagery in subjects with different hypnotic susceptibility

The autonomic and EEG correlates of the response to a cognitive unpleasant stimulation (US) verbally administered to awake hypnotizable and non hypnotizable subjects were studied. They were compared with the values obtained during a resting condition immediately preceding the stimulus and with those produced by a cognitive neutral stimulation (NS), also administered after a basal resting period. Results showed hypnotic trait effects on skin resistance, heart and respiratory rate as well as on EEG theta, alpha, beta and gamma relative power changes. The autonomic and EEG patterns observed indicated different strategies in the task execution for hypnotizable and non hypnotizable subjects and a discrepancy between the autonomic and EEG changes associated to the US in susceptible subjects. Results support dissociation theories of hypnosis and suggest for hypnotizable persons an active mechanism of protection against cardiac hazard.

Does hypnotizability modulate the stress-related endothelial dysfunction?

Previous studies suggest that hypnotizability represents a protective factor against the cardiac effects of cognitive stress and that hypnosis prevents vascular stress-induced modifications in highly hypnotizable individuals. The aim of the experiment was to investigate whether a similar effect at vascular level is present in awake subjects with a high (Highs) and a low (Lows) hypnotic susceptibility. Thus, brachial artery post-ischaemic flow-mediated vascular dilation (FMD) was evaluated non-invasively by ultrasound methodology during cognitive stress (mental computation) in Highs and Lows. Results showed that Highs, similarly to that previously observed in hypnotized Highs and in contrast with Lows, did not exhibit any stress-related endothelial dysfunction (FMD decrement). Thus, hypnotizability should be considered a protective factor against vascular disease.

Changes in autonomic and EEG patterns induced by hypnotic imagination of aversive stimuli in man

Autonomic and electroencephalographic (EEG) responses to aversive stimuli presented by means of hypnotic suggestion have been studied in man.Healthy volunteers with simple phobia were screened for susceptibility to hypnosis. The experimental paradigm included periods of rest during which the hypnotized subjects were asked to produce an emotionally neutral mental image and periods of emotional activation in which they were asked to image a phobic object. Heart rate (HR), respiratory frequency (RF) and EEG were processed to obtain the HR-related indexes of sympatho-vagal balance and the EEG spectral components. The results showed a significant increase in HR and RF with a shift of the sympatho-vagal indexes towards a sympathetic predominance during the hypnotic emotional activation. EEG activity showed a significant increase in the gamma band with a left fronto-central prevalence. There was also a less pronounced increase in the beta band. In conclusion, by means of hypnosis, autonomic and behavioral responses to fear-like stimuli can be induced in man in a reproducible and controlled manner. Such a paradigm could be applied in human neuroimaging studies to identify central nervous structures that modulate stress and fear-related reactions.

Hypnotizability-related integration of perception and action

Hypnotizability is a cognitive trait able to modulate many behavioural/physiological processes and associated with peculiar functional characteristics of the frontal executive system. This review summarizes experimental results on hypnotizability-related differences in sensorimotor integration at a reflex and an integrated level (postural control) and suggests possible interpretations based on morpho-functional considerations. In particular, hypnotizability-related differences in spinal motoneurones excitability are described, and the role of attention and imagery in maintaining a stable upright stance when sensory information is reduced or altered and when attention is absorbed in cognitive tasks is discussed as a function of hypnotic susceptibility. The projections from prefrontal cortex to spinal motoneurones and the balance between the activation of the right and left cortical hemisphere are considered responsible for the hypnotizability-related modulation of reflex responses, while the differences in postural control between subjects with high (highs) and low (lows) hypnotic susceptibility are considered a possible consequence of the activity of the locus coeruleus, which is also involved in attention, and of the cerebellum, which might be responsible for different internal models of postural control. We suggest a highly pervasive role of hypnotic susceptibility in human behaviour through the modulation of the integration of perception and action, which could be relevant for neurorehabilitative treatments and for the adaptation to special environments.

Hypnotizability-dependent modulation of postural control: effects of alteration of the visual and leg proprioceptive inputs.

The aim of the experiment was to investigate whether the peculiar attentional/imagery abilities associated with susceptibility to hypnosis might make postural control in highly hypnotizable subjects (Highs) that are less vulnerable to sensory alteration than in individuals with low hypnotic susceptibility (Lows). The movement of the centre of pression (CoP) was monitored in Highs and Lows during alteration of the visual and leg proprioceptive input. The two groups responded differently to eyes closure and to an unstable support and the CoP movement was generally larger and faster in Highs. The stabilogram diffusion analysis indicated a different set point in Highs and Lows and suggested that the former are more independent of specific sensory information than the latter, likely due to different abilities in sensory re-weighting and/or peculiar internal models of postural control. The results are discussed within the general perspective of high pervasiveness of the hypnotizability trait, which modulates cognitive, autonomic and somatic functions.

Effects of vestibular and neck proprioceptive stimulation on posture as a function of hypnotizability.

Abstract Previous studies on the role of hypnotizability in postural control indicate that the body sway of subjects with high or low hypnotizability to hypnosis is differentially modulated by eye closure. The aim of this study was to investigate whether hypnotizability also modulates the postural response to electrical vestibular stimulation and to head rotation in nonhypnotized individuals. The center of pressure (CoP) displacements were monitored in highs and lows standing on a stabilometric platform with closed eyes during basal conditions and electrical vestibular stimulation in 3 different positions of the head. Results showed that the CoP stimulus-locked displacements as well as the CoP mean position, area, and mean velocity were similar in highs and lows, but only in lows did the head position modulate the mean velocity. This finding might reflect a difference in sensory-motor integration between the 2 groups.

Imagery of different sensory modalities: hypnotizability and body sway.

Postural control in subjects with high (Highs) and low (Lows) susceptibility to hypnosis is differentially affected by changes in visual and neck tactile/proprioceptive input. The aim of the present experiment was to investigate whether imagery of the visual and tactile sensory modalities also induces different modulation of postural control in Highs and Lows. Fourteen Highs and 16 Lows were included in the study; they were recorded while standing upright with eyes closed during visual and tactile imagery tasks and during mental computation. Their posture and movement were recorded with an Elite System and their experience was assessed after each task in a structured interview. Visual imagery was judged “easier” than tactile imagery by Lows, while Highs performed both tasks easily and judged the tactile imagery less effortful and more vivid than Lows. No difference was observed for the mental computation. The Highs’ body sway was not affected by the cognitive tasks, while Lows showed a task-related modulation of body sway. The results are in line with the hypothesis of lower vulnerability of Highs to the effects of tasks interfering with postural control and of different sensory-motor integration in Highs and Lows.

Can imagery become reality

Previous studies showed that highly hypnotizable persons imagining a specific sensory context behave according to the corresponding real stimulation and perceive their behaviour as involuntary. The aim of the study was to confirm the hypothesis of a translation of sensory imagery into real perception and, thus, of a true involuntary response. We studied the imagery-induced modulation of the vestibulospinal (VS) reflex earlier component in highly (Highs) and low hypnotizable subjects (Lows), as it is not affected by voluntary control, its amplitude depends on the stimulus intensity, and the plane of body sway depends on the position of the head with respect to the trunk. Results showed that the effects of the “obstructive” imagery of anaesthesia are different from those elicited by the “constructive” imagery of head rotation. Indeed, both Highs and Lows having their face forward and reporting high vividness of imagery experienced anaesthesia and reduced their VS reflex amplitude in the frontal plane, while only Highs changed the plane of body sway according to the imagined head rotation that is from the frontal to the sagittal one. These effects cannot be voluntary and should be attributed to translation of sensory imagery into the corresponding real perception.