Eleonora Castellani

Hypnotic assessment based on the Recurrence Quantification Analysis of EEG recorded in the ordinary state of consciousness.

The cerebral cortical correlates of the susceptibility to hypnosis in the ordinary states of consciousness have not been clarified. Aim of the study was to characterize the EEG dynamics of subjects with high (highs) and low hypnotisability (lows) through the non-linear method of Recurrence Quantification Analysis (RQA). The EEG of 16 males--8 highs and 8 lows--was monitored for 1min without instructions other than keeping the eyes closed, being silent and avoiding movements (short resting), and during 15 min of simple relaxation, that is with the instruction to relax at their best. Highs and lows were compared on the RQA measures of Determinism (DET) and Entropy (ENT), which are related to the signal determinism and complexity. In the short resting condition discriminant analysis could classify highs and lows on the basis of DET and ENT values at temporo-parietal sites. Many differences in DET and all differences in ENT disappeared during simple relaxation, although DET still separated the two groups in the earliest 6min of relaxation at temporo-parietal sites. Our RQA based approach allows to develop computer-based methods of hypnotic assessment using short-lasting, single channel EEG recordings analyzed through standard mathematical methods.

Emotion processing without awareness: features detection or significance evaluation?

Studies on the physiological responses to emotional stimuli demonstrated that they can occur even when emotional stimuli are not consciously perceived. In this study, the subliminal stimulation was obtained by means of Backward Masking. Specifically, we analyzed the cardiac and electrodermal responses evoked by the unmasked and masked presentation of spider shapes in arachnophobic individuals. To evaluate whether unaware processing entails discrimination of physical features vs emotional significance, crabs, morphologically similar to the spiders but different for emotional significance, and squirrels, different in both shape and emotional content, were also employed. The response to unmasked spiders consisted of a typical defense response (sympathetic activation), while that to innocuous stimuli of an orienting response (moderate electrodermal and vagal activations). In the subliminal condition, the electrodermal response to masked spiders was greater than that to the other animals suggesting an early detection of emotional content rather than of physical characteristics. In contrast, cardiac responses to the masked stimuli did not show any differences as a function of valence. These findings suggest that individuals can appraise the emotional content of unconsciously perceived stimuli and react with an arousal response. However, subliminal emotional stimuli does not seem able to elicit the complete pattern of autonomic responses typical of the defense response.

Visual Identification of Haptically Explored Objects in High and Low Hypnotizable Subjects

Abstract Hypnotizability is associated with peculiar characteristics of sensorimotor integration, imaginal abilities, and preferences in the sensory modality of imagery. The visual recognition of haptically explored objects involves an interaction among these processes and is a proper tool to investigate their possible hypnotizability-related modulation. Sixteen high hypnotizables and 16 lows participated in the study. Higher frequencies of correct recognition (RF) were observed in highs. RF improved across both groups. As an effect of learning, shorter recognition times were found in males among highs and in females among lows. The findings are consistent with the literature suggesting that hypnotizability levels may be associated with specific modes of sensory integration and/or imagery.

Pain-inducing imagery as a function of hypnotisability and of the activity of Gray's Behavioral Inhibition/Activation Systems.

The aim of the study was to test the efficacy of pain imagery as a function of hypnotisability and of the activity of Behavioral Inhibition/Activation Systems. Questionnaires of imagery abilities (Betts) for the visual, cutaneous and organic modalities, absorption in cognitive tasks (TAS), proneness to inhibit stressful/painful experience/seek out positive experiences (BIS BAS), trait anxiety (STAI-Y2) and psychological well-being (PWB) were administered to 21 subjects with high hypnotisability (highs) and 21 subjects with low hypnotisability (lows). Self-reports of pain intensity and of neutral tactile perception were collected during imagery of nociceptive (Pain) and neutral tactile stimulation (NT). ECG and skin conductance were recorded. Highs exhibited greater imagery abilities, absorption, Behavioral Inhibition System Activity and psychological well-being with respect to lows. They reported lower scores of pain intensity than of tactile perception, while in lows Pain and NT scores did not differ. However, controlling for BAS, but not for BIS, revealed differences in the efficacy of pain imagery between highs and lows. Heart rate decreased in both tasks and groups; heart rate variability and skin conductance did not change significantly during imageries. Our findings suggest that the Behavioral Inhibition/Activation Systems interact with imagery abilities reducing the efficacy of pain imagery and prompt investigation of possible similar interactions in the modulation of physically induced experimental pain and of chronic pain in the general population.

Selective delayed gains following motor imagery of complex movements

Recent studies suggest that a night of sleep may play a similar functional role following motor imagery (MI) practice. Here we examined whether offline gains following MI of a finger tapping sequence depends on the degree of complexity of the motor sequence, and whether this improvement differentially affects the individual transitions of the motor-sequence pattern being learned. The data revealed greater delayed performance gains in motor skill procedures that were most difficult, with larger sleep-dependent overnight improvement for movements involving bimanual coordination. The analyses of single transitions between sequence elements further revealed greatest overnight improvement in speed for the slowest (i.e., most difficult) transitions at the re-test. These findings suggest that sleep-related performance gains for imagined movements depend on motor skill complexity, and that difficult transition movements are most effectively enhanced after a night of sleep.

Inefficient stimulus processing at encoding affects formation of high-order general representation: A study on cross-modal word-stem completion task

Priming is an implicit memory effect in which previous exposure to one stimulus influences the response to another stimulus. The main characteristic of priming is that it occurs without awareness. Priming takes place also when the physical attributes of previously studied and test stimuli do not match; in fact, it greatly refers to a general stimulus representation activated at encoding independently of the sensory modality engaged. Our aim was to evaluate whether, in a cross-modal word-stem completion task, negative priming scores could depend on inefficient word processing at study and therefore on an altered stimulus representation. Words were presented in the auditory modality, and word-stems to be completed in the visual modality. At study, we recorded auditory ERPs, and compared the P300 (attention/memory) and N400 (meaning processing) of individuals with positive and negative priming. Besides classical averaging-based ERPs analysis, we used an ICA-based method (ErpICASSO) to separate the potentials related to different processes contributing to ERPs. Classical analysis yielded significant difference between the two waves across the whole scalp. ErpICASSO allowed separating the novelty-related P3a and the top-down control-related P3b sub-components of P300. Specifically, in the component C3, the positive deflection identifiable as P3b, was significantly greater in the positive than in the negative priming group, while the late negative deflection corresponding to the parietal N400, was reduced in the positive priming group. In conclusion, inadequacy of specific processes at encoding, such as attention and/or meaning retrieval, could generate weak semantic representations, making words less accessible in subsequent implicit retrieval.

Pain perception and EEG dynamics: Does hypnotizability account for the efficacy of the suggestions of analgesia?

We report novel findings concerning the role of hypnotizability, suggestions of analgesia and the activity of the Behavioral Inhibition/Activation System (BIS/BAS) in the modulation of the subjective experience of pain and of the associated EEG dynamics. The EEG of high (highs) and low hypnotizable participants (lows) who completed the BIS/BAS questionnaire was recorded during basal conditions, tonic nociceptive stimulation without (PAIN) and with suggestions for analgesia (AN). Participants scored the perceived pain intensity at the end of PAIN and AN. The EEG midline dynamics was characterized by indices indicating the signal predictability (Determinism) and complexity (Entropy) obtained through the Recurrence Quantification Analysis. The reduced pain intensity reported by highs during AN was partially accounted for by the activity of the Behavioral Activation System. The decreased midline cortical Determinism observed during nociceptive stimulation in both groups independently of suggestions remained significantly reduced only in lows after controlling for the activity of the Behavioral Activation System. Finally, controlling for the activity of the Behavioral Inhibition System abolished stimulation, suggestions and hypnotizability-related differences. Results indicate that the BIS/BAS activity may be more important than hypnotizability itself in pain modulation and in the associated EEG dynamics.

Declarative interference affects off-line processing of motor imagery learning during both sleep and wakefulness

Retroactive interference from a declarative memory can prevent the consolidation of motor skill memories over wakefulness, but not over a night of sleep. Recently, motor imagery (MI) learning has been showed to allow for a stronger resistance against procedural interference rather than physical practice, but whether declarative interference might impact sleep-dependent consolidation process of an explicit finger tapping task learned with MI remains unknown. To address this issue, 57 subjects mentally rehearsed an explicit finger tapping sequence, and half of them were then requested to practice an interferential declarative task. All participants were re-tested on the initial procedural task either after a night of sleep or a similar daytime interval. The main findings provided evidence that declarative interference affected MI consolidation both over the night- and wakefulness intervals. These results extend our previous findings by underlying that declarative interference might impact more strongly explicit MI practice than physical practice, hence suggesting that MI might rely on declarative memory rather than exclusively on procedural memory system. The relationship between declarative and procedural memories during MI practice, as well as during off-line consolidation, is discussed.

Cross-evidence for hypnotic susceptibility through nonlinear measures on EEGs of non-hypnotized subjects

Assessment of hypnotic susceptibility is usually obtained through the application of psychological instruments. A satisfying classification obtained through quantitative measures is still missing, although it would be very useful for both diagnostic and clinical purposes. Aiming at investigating the relationship between the cortical brain activity and the hypnotic susceptibility level, we propose the combined use of two methodologies - Recurrence Quantification Analysis and Detrended Fluctuation Analysis - both inherited from nonlinear dynamics. Indicators obtained through the application of these techniques to EEG signals of individuals in their ordinary state of consciousness allowed us to obtain a clear discrimination between subjects with high and low susceptibility to hypnosis. Finally a neural network approach was used to perform classification analysis.