Influence of body position on cortical pain-related somatosensory processing: an ERP study

The temporal effect of uncertain context on the perceptual processing of painful and non-painful stimulation

Uncertainty has been demonstrated to influence the perception of noxious stimuli, but little is known about the effects of prolonged uncertain contexts on the perception of painful and non-painful stimuli. To address this knowledge gap, the present study utilized a cue-based NPU-threat task, where uncertain and certain trials were separated into distinct blocks. The objective was to investigate the impact of uncertain contexts on the temporal dynamics of electroencephalogram (EEG) activity during the processing of painful and non-painful stimuli. The results revealed that the influence of uncertain contexts on neural responses extends beyond painful trials and is also evident in non-painful trials. In uncertain contexts, it has been observed that painful stimuli elicit larger P2 amplitudes and late beta band (13-30 Hz) event-related desynchronization (ERD) around 500-700 ms. However, in certain contexts, painful stimuli evoke stronger late gamma band (50-70 Hz) event-related synchronization (ERS) around 600-700 ms. For non-painful trials, in uncertain contexts, significantly higher amplitudes of the late positive potential (LPP) component and delta-theta band (2-7 Hz) ERS were observed compared to certain non-painful stimuli. These findings demonstrate that uncertain contexts exert a significant impact on the processing of both painful and non-painful stimuli, and this influence is mediated by distinct neural mechanisms.

Modulation of vestibular input by short-term head-down bed rest affects somatosensory perception: implications for space missions

Introduction

On Earth, self-produced somatosensory stimuli are typically perceived as less intense than externally generated stimuli of the same intensity, a phenomenon referred to as somatosensory attenuation (SA). Although this phenomenon arises from the integration of multisensory signals, the specific contribution of the vestibular system and the sense of gravity to somatosensory cognition underlying distinction between self-generated and externally generated sensations remains largely unknown. Here, we investigated whether temporary modulation of the gravitational input by head-down tilt bed rest (HDBR)-a well-known Earth-based analog of microgravity-might significantly affect somatosensory perception of self- and externally generated stimuli.

Methods

In this study, 40 healthy participants were tested using short-term HDBR. Participants received a total of 40 non-painful self- and others generated electrical stimuli (20 self- and 20 other-generated stimuli) in an upright and HDBR position while blindfolded. After each stimulus, they were asked to rate the perceived intensity of the stimulation on a Likert scale.

Results

Somatosensory stimulations were perceived as significantly less intense during HDBR compared to upright position, regardless of the agent administering the stimulus. In addition, the magnitude of SA in upright position was negatively correlated with the participants' somatosensory threshold. Based on the direction of SA in the upright position, participants were divided in two subgroups. In the subgroup experiencing SA, the intensity rating of stimulations generated by others decreased significantly during HDBR, leading to the disappearance of the phenomenon of SA. In the second subgroup, on the other hand, reversed SA was not affected by HDBR.

Conclusion

Modulation of the gravitational input by HDBR produced underestimation of somatosensory stimuli. Furthermore, in participants experiencing SA, the reduction of vestibular inputs by HDBR led to the disappearance of the SA phenomenon. These findings provide new insights into the role of the gravitational input in somatosensory perception and have important implications for astronauts who are exposed to weightlessness during space missions.

Midfrontal theta oscillation encodes haptic delay

Haptic technologies aim to simulate tactile or kinesthetic interactions with a physical or virtual environment in order to enhance user experience and/or performance. However, due to stringent communication and computational needs, the user experience is influenced by delayed haptic feedback. While delayed feedback is well understood in the visual and auditory modalities, little research has systematically examined the neural correlates associated with delayed haptic feedback. In this paper, we used electroencephalography (EEG) to study sensory and cognitive neural correlates caused by haptic delay during passive and active tasks performed using a haptic device and a computer screen. Results revealed that theta power oscillation was significantly higher at the midfrontal cortex under the presence of haptic delay. Sensory correlates represented by beta rebound were found to be similar in the passive task and different in the active task under the delayed and synchronous conditions. Additionally, the event related potential (ERP) P200 component is modulated under the haptic delay condition during the passive task. The P200 amplitude significantly reduced in the last 20% of trials during the passive task and in the absence of haptic delay. Results suggest that haptic delay could be associated with increased cognitive control processes including multi-sensory divided attention followed by conflict detection and resolution with an earlier detection during the active task. Additionally, haptic delay tends to generate greater perceptual attention that does not significantly decay across trials during the passive task.

Peripheral nerve adaptations to 10 days of horizontal bed rest in healthy young adult males

Space analogs, such as bed rest, are used to reproduce microgravity-induced morphological and physiological changes and can be used as clinical models of prolonged inactivity. Nevertheless, nonuniform decreases in muscle mass and function have been frequently reported, and peripheral nerve adaptations have been poorly studied, although some of these mechanisms may be explained. Ten young healthy males (18-33 yr) underwent 10 days of horizontal bed rest. Peripheral neurophysiological assessments were performed bilaterally for the dominant (DL) and nondominant upper and lower limbs (N-DL) on the 1st and 10th day of bed rest, including ultrasound of the median, deep peroneal nerve (DPN), and common fibular nerve (CFN) , as well as a complete nerve conduction study (NCS) of the upper and lower limbs. Consistently, reduced F waves, suggesting peripheral nerve dysfunction, of both the peroneal (DL: P = 0.005, N-DL: P = 0.013) and tibial nerves (DL: P = 0.037, N-DL: P = 0.005) were found bilaterally, whereas no changes were observed in nerve ultrasound or other parameters of the NCS of both the upper and lower limbs. In these young healthy males, only the F waves, known to respond to postural changes, were significantly affected by short-term bed rest. These preliminary results suggest that during simulated microgravity, most changes occur at the muscle or central nervous system level. Since the assessment of F waves is common in clinical neurophysiological examinations, caution should be used when testing individuals after prolonged immobility.

Effects of head-down tilt bed rest plus elevated CO2 on cognitive performance

Microgravity and elevated CO₂ levels are two important environmental spaceflight stressors that can adversely affect astronaut cognitive performance and jeopardize mission success. This study investigated the effects of 6° head-down tilt bed rest (HDBR) with (n = 11 participants, 30-day HDBR) and without (n = 8 participants, 60-day HDBR) elevated ambient (3.73 mmHg) CO₂ concentrations on cognitive performance. Participants of both groups performed all 10 tests of NASA's Cognition battery and a brief alertness and mood survey repeatedly before, during, and after the HDBR period. Test scores were adjusted for practice and stimulus set effects. Concentrating on the first 30 days of HDBR, a modest but statistically significant slowing across a range of cognitive domains was found in both groups (controls: -0.37 SD; 95% CI -0.48, -0.27; adjusted P < 0.0001; CO₂: -0.25 SD; 95% CI -0.34, -0.16; adjusted P < 0.001), most prominently for sensorimotor speed. These changes were observed early during HDBR and did not further deteriorate or improve with increasing time in HDBR. The study found similar cognitive effects of HDBR irrespective of CO₂ levels, suggesting that elevated CO₂ neither ameliorated nor worsened the HDBR effects. In both groups, cognitive performance after 15 days of recovery was statistically indistinguishable from pre-HDBR performance. However, subjects undergoing 60 days of HDBR rated themselves as feeling more sleepy, tired, physically exhausted, stressed, and unhealthy during recovery compared to their 30-day counterparts.NEW AND NOTEWORTHY This study investigated the effects of prolonged head-down tilt bed rest with and without elevated (3.73 mmHg) levels of ambient CO₂ on cognitive performance across a range of cognitive domains and is one of the few studies investigating combined effects of environmental stressors prevalent in spaceflight. The study showed moderate declines in cognitive speed induced by head-down tilt bed rest and suggests that exposure to elevated levels of ambient CO₂ did not modify this effect.

Neurophysiological adaptations to spaceflight and simulated microgravity

Changes in physiological functions after spaceflight and simulated spaceflight involve several mechanisms. Microgravity is one of them and it can be partially reproduced with models, such as head down bed rest (HDBR). Yet, only a few studies have investigated in detail the complexity of neurophysiological systems and their integration to maintain homeostasis. Central nervous system changes have been studied both in their structural and functional component with advanced techniques, such as functional magnetic resonance (fMRI), showing the main involvement of the cerebellum, cortical sensorimotor, and somatosensory areas, as well as vestibular-related pathways. Analysis of electroencephalography (EEG) led to contrasting results, mainly due to the different factors affecting brain activity. The study of corticospinal excitability may enable a deeper understanding of countermeasures' effect, since greater excitability has been shown being correlated with better preservation of functions. Less is known about somatosensory evoked potentials and peripheral nerve function, yet they may be involved in a homeostatic mechanism fundamental to thermoregulation. Extending the knowledge of such alterations during simulated microgravity may be useful not only for space exploration, but for its application in clinical conditions and for life on Earth, as well.

Processing of Painful Pictures in Individuals With High and Low Rejection Sensitivity: Evidence From Event-Related Potentials

An increasing number of studies have investigated the relation between the processing of painful stimuli and rejection. Little was known, however, about the impact of the rejection sensitivity (RS) on the processing of painful pictures. This study addressed this issue using high temporal resolution event-related potential techniques. Thirty high RS (20 women and 10 men who scored in the top 20th percentile of the Rejection Sensitivity Questionnaire scores) and 30 low RS (20 women and 10 men who scored in the bottom 20th percentile) volunteers participated in the experiment. All volunteers performed a discrimination task of painful pictures in which they were asked to judge whether target pictures were painful or not. Behaviorally, participants exhibited shorter reaction times for painful than nonpainful pictures. For the P100 component, low RS participants showed stronger brain activities for painful than nonpainful pictures, suggesting vigilance toward painful pictures. High RS participants, however, exhibited no P100 amplitude differences between painful and nonpainful pictures, indicating an analgesia phenomenon. Furthermore, we found that there were larger amplitudes in the late late positive complex component for painful compared with nonpainful pictures, regardless of participants' RS. This suggested a person's further assessment for painful pictures. In short, our findings demonstrated that the level of RS influenced the pain processing at a very early stage of processing.

Modality-specific effects of aversive expectancy in the anterior insula and medial prefrontal cortex

Expectations modulate the subjective experience of pain by increasing sensitivity to nociceptive inputs, an effect mediated by brain regions such as the insula. However, it is still unknown whether the neural structures underlying pain expectancy hold sensory-specific information or, alternatively, code for modality-independent features (eg, unpleasantness), potentially common with other negative experiences. We used functional magnetic resonance imaging to investigate neural activity underlying the expectation of different, but comparably unpleasant, pain and disgust. We presented participants with visual cues predicting either a painful heat or disgusting odor, and assessed how they affected the subsequent subjective experience of stimuli from the same (within-modality) or opposite (cross-modal) modality. We found a reliable influence of expectancy on the subjective experience of stimuli whose modality matched that of the previous cue. At the brain level, this effect was mediated by the intermediate dysgranular section of the insula, whereas it was suppressed by more anterior agranular portions of the same region. Instead, no expectancy modulation was observed when the modality of the cue differed from that of the subsequent stimulus. Our data suggest that the insular cortex encodes prospective aversive events in terms of their modality-specific features, and whether they match with subsequent stimulations.

The Circadian Rhythm of Breakthrough Pain Episodes in Terminally-ill Cancer Patients

Opioid therapy must be adjusted to the rhythm of a cancer patient’s pain to ensure adequate symptom control at the end of life (EOL). However, to-date no study has explored the rhythm of breakthrough pain (BTP) episodes in terminally-ill cancer patients. This prospective longitudinal study was aimed at verifying the existence of a circadian rhythm of BTP episodes in terminally-ill cancer patients. Consecutive adult cancer patients at their EOL treated with long-acting major opioids to control background pain (Numeric Rating Scale ≤ 3/10) were recruited from two Italian palliative care services. Using a personal diary, patients recorded the frequency and onset of BTP episodes and the analgesic rescue therapy taken for each episode over a 7-day period. Rhythms identified in BTP episodes were validated by Cosinor analysis. Overall, 101 patients were enrolled; nine died during the study period. A total of 665 BTP episodes were recorded (average of 7.2 episodes, mean square error 0.8) per patient, with 80.6% of episodes recorded between 8:00 a.m. and 12:00 a.m. At Cosinor analysis, a circadian rhythm of BTP episodes was observed, with a Midline Estimating Statistics of the Rhythm (MESOR) of 1.5, a double amplitude of 1.8, and an acrophase at 12:30 p.m. (p < 0.001). Oral morphine was the most frequent analgesic rescue therapy employed. In terminally-ill cancer patients, BTP episodes follow a circadian rhythm; thus, tailoring the timing of opioid administration to this rhythm may prevent such episodes. This circadian rhythm of BTP episodes in terminally-ill cancer patients should be confirmed in larger samples.

Posture Used in fMRI-PET Elicits Reduced Cortical Activity and Altered Hemispheric Asymmetry with Respect to Sitting Position: An EEG Resting State Study

Horizontal body position is a posture typically adopted for sleeping or during brain imaging recording in both neuroscience experiments and diagnostic situations. Recent literature showed how this position and similar ones with head down are associated to reduced plasticity, impaired pain and emotional responses. The present study aimed at further understanding the decrease of cortical activity associated with horizontal body position by measuring high-frequency EEG bands – typically associated with high-level cognitive activation – in a resting state experimental condition. To this end, two groups of 16 female students were randomly assigned to either sitting control (SC) or 2-h horizontal Bed Rest condition (hBR) while EEG was recorded from 38 scalp recording sites. The hBR group underwent several body transitions, from sitting to supine, and from supine to sitting. Results revealed a clear effect of horizontal posture: the hBR group showed, compared to its baseline and to SC, reduced High-Beta and Gamma EEG band amplitudes throughout the 2-h of hBR condition. In addition, before and after the supine condition, hBR group as well as SC exhibited a greater left vs. right frontal activation in both EEG bands while, on the contrary, the supine position induced a bilateral and reduced activation in hBR participants. The cortical sources significantly more active in SC compared with hBR participants included the left Inferior Frontal Gyrus and left Insula. Results are discussed in relation to the differences among neuroimaging methods (e.g., fMRI, EEG, NIRS), which can be partially explained by posture-induced neural network changes.

Influence of transient spatial attention on the P3 component and perception of painful and non-painful electric stimuli in crossed and uncrossed hands positions

Recent reports show that focusing attention on the location where pain is expected can enhance its perception. Moreover, crossing the hands over the body’s midline is known to impair the ability to localise stimuli and decrease tactile and pain sensations in healthy participants. The present study investigated the role of transient spatial attention on the perception of painful and non-painful electrical stimuli in conditions in which a match or a mismatch was induced between skin-based and external frames of reference (uncrossed and crossed hands positions, respectively). We measured the subjective experience (Numerical Rating Scale scores) and the electrophysiological response elicited by brief electric stimuli by analysing the P3 component of Event-Related Potentials (ERPs). Twenty-two participants underwent eight painful and eight non-painful stimulus blocks. The electrical stimuli were applied to either the left or the right hand, held in either a crossed or uncrossed position. Each stimulus was preceded by a direction cue (leftward or rightward arrow). In 80% of the trials, the arrow correctly pointed to the spatial regions where the stimulus would appear (congruent cueing). Our results indicated that congruent cues resulted in increased pain NRS scores compared to incongruent ones. For non-painful stimuli such an effect was observed only in the uncrossed hands position. For both non-painful and painful stimuli the P3 peak amplitudes were higher and occurred later for incongruently cued stimuli compared to congruent ones. However, we found that crossing the hands substantially reduced the cueing effect of the P3 peak amplitudes elicited by painful stimuli. Taken together, our results showed a strong influence of transient attention manipulations on the NRS ratings and on the brain activity. Our results also suggest that hand position may modulate the strength of the cueing effect, although differences between painful and non-painful stimuli exist.

Supine posture affects cortical plasticity in elderly but not young women during a word learning-recognition task

The present research investigated the hypothesis that elderly and horizontal body position contribute to impair learning capacity. To this aim, 30 young (mean age: 23.2 years) and 20 elderly women (mean age: 82.8 years) were split in two equal groups, one assigned to the Seated Position (SP), and the other to the horizontal Bed Rest position (hBR). In the Learning Phase, participants were shown 60 words randomly distributed, and in the subsequent Recognition Phase they had to recognize them mixed with a sample of 60 new words. Behavioral analyses showed age-group effects, with young women exhibiting faster response times and higher accuracy rates than elderly women, but no interaction of body position with age group was found. Analysis of the RP component (250-270ms) revealed greater negativity in the left Occipital gyrus/Cuneus of both sitting age-groups, but significantly left-lateralized RP in left Lingual gyrus only in young bedridden women. Elderly hBR women showed a lack of left RP lateralization, the main generator being located in the right Cuneus. Young participants had the typical old/new effect (450-800ms) in different portions of left Frontal gyri/Uncus, whereas elderly women showed no differences in stimulus processing and its location. EEG alpha activity analyzed during a 3min resting state, soon after the recognition task, revealed greater alpha amplitude (i.e., cortical inhibition) in posterior sites of hBR elderly women, a result in line with their inhibited posterior RP. In elderly women the left asymmetry of RP was positively correlated with both greater accuracy and faster responses, thus pointing to a dysfunctional role, rather than a compensatory shift, of the observed right RP asymmetry in this group. This finding may have important clinical implications, with particular regard to the long-term side-effects of forced Bed Rest on elderly patients.

Source Localization of Brain States Associated with Canonical Neuroimaging Postures

Cognitive neuroscientists rarely consider the influence that body position exerts on brain activity; yet, postural variation holds important implications for the acquisition and interpretation of neuroimaging data. Whereas participants in most behavioral and EEG experiments sit upright, many prominent brain imaging techniques (e.g., fMRI) require participants to lie supine. Here we demonstrate that physical comportment profoundly alters baseline brain activity as measured by magnetoencephalography (MEG)-an imaging modality that permits multipostural acquisition. We collected resting-state MEG data from 12 healthy participants in three postures (lying supine, reclining at 45°, and sitting upright). Source-modeling analysis revealed a broadly distributed influence of posture on resting brain function. Sitting upright versus lying supine was associated with greater high-frequency (i.e., beta and gamma) activity in widespread parieto-occipital cortex. Moreover, sitting upright and reclining postures correlated with dampened activity in prefrontal regions across a range of bandwidths (i.e., from alpha to low gamma). The observed effects were large, with a mean Cohen's d of 0.95 ( SD = 0.23). In addition to neural activity, physiological parameters such as muscle tension and eye blinks may have contributed to these posture-dependent changes in brain signal. Regardless of the underlying mechanisms, however, the present results have important implications for the acquisition and interpretation of multimodal imaging data (e.g., studies combining fMRI or PET with EEG or MEG). More broadly, our findings indicate that generalizing results-from supine neuroimaging measurements to erect positions typical of ecological human behavior-would call for considering the influence that posture wields on brain dynamics.

Imaging Posture Veils Neural Signals

Whereas modern brain imaging often demands holding body positions incongruent with everyday life, posture governs both neural activity and cognitive performance. Humans commonly perform while upright; yet, many neuroimaging methodologies require participants to remain motionless and adhere to non-ecological comportments within a confined space. This inconsistency between ecological postures and imaging constraints undermines the transferability and generalizability of many a neuroimaging assay. Here we highlight the influence of posture on brain function and behavior. Specifically, we challenge the tacit assumption that brain processes and cognitive performance are comparable across a spectrum of positions. We provide an integrative synthesis regarding the increasingly prominent influence of imaging postures on autonomic function, mental capacity, sensory thresholds, and neural activity. Arguing that neuroimagers and cognitive scientists could benefit from considering the influence posture wields on both general functioning and brain activity, we examine existing imaging technologies and the potential of portable and versatile imaging devices (e.g., functional near infrared spectroscopy). Finally, we discuss ways that accounting for posture may help unveil the complex brain processes of everyday cognition.

Supine posture inhibits cortical activity: Evidence from Delta and Alpha EEG bands

Past studies have shown consistent evidence that body position significantly affects brain activity, revealing that both head-down and horizontal bed-rest are associated with cortical inhibition and altered perceptual and cognitive processing. The present study investigates the effects of body position on spontaneous, open-eyes, resting-state EEG cortical activity in 32 young women randomly assigned to one of two conditions, seated position (SP) or horizontal bed rest (BR). A between-group repeated-measure experimental design was used, EEG recordings were made from 38 scalp locations, and low-frequency (delta and alpha) amplitudes of the two groups were compared in four different conditions: when both groups (a) were seated (T0), (b) assumed two different body positions (seated vs. supine conditions, immediate [T1] and 120min later [T2]), and (c) were seated again (T3). Overall, the results showed no a priori between-group differences (T0) before experimental manipulation. As expected, delta amplitude, an index of cortical inhibition in awake resting participants, was significantly increased in group BR, revealing both rapid (T1) and mid-term (T2) inhibitory effects of supine or horizontal positions. Instead, the alpha band was highly sensitive to postural transitions, perhaps due to baroreceptor intervention and, unlike the delta band, underwent habituation and decreased after a 2-h bed rest. These results indicate clear-cut differences at rest between the seated and supine positions, thus supporting the view that the role of body position in the differences found between brain metabolic methods (fMRI and PET) in which participants lie horizontally, and EEG-MEG-TMS techniques with participants in a seated position, has been largely underestimated so far.

Posture alters human resting-state

Neuroimaging is ubiquitous; however, neuroimagers seldom investigate the putative impact of posture on brain activity. Whereas participants in most psychological experiments sit upright, many prominent neuroimaging techniques (e.g., functional magnetic resonance imaging (fMRI)) require participants to lie supine. Such postural discrepancies may hold important implications for brain function in general and for fMRI in particular. We directly investigated the effect of posture on spontaneous brain dynamics by recording scalp electrical activity in four orthostatic conditions (lying supine, inclined at 45°, sitting upright, and standing erect). Here we show that upright versus supine posture increases widespread high-frequency oscillatory activity. Our electroencephalographic findings highlight the importance of posture as a determinant in neuroimaging. When generalizing supine imaging results to ecological human cognition, therefore, cognitive neuroscientists would benefit from considering the influence of posture on brain dynamics.

Horizontal body position reduces cortical pain-related processing: evidence from late ERPs

The present study investigated the influence of short-term horizontal body position on pain-related somatosensory processing, by measuring subjective and cortical responses to electrical pain stimulation. Twenty-eight healthy women were randomly assigned to either the experimental horizontal group (Bed Rest, BR) or to the sitting control group (Sitting Control, SC). After 90 minutes in either horizontal or sitting position, the individual pain thresholds were assessed and EEG/self-evaluations recorded during the administration of 180 stimuli delivered to the left forearm. Electrical pain stimuli, calibrated to subjects’ individual pain thresholds, consisted of two different intensity levels: no pain (40% below pain threshold) and pain (40% above pain threshold). Compared with control, BR condition significantly inhibited subjective sensitivity to painless stimuli, whereas electrophysiological results pointed to a reduced slow cortical wave (interval: 300-600 ms) at all stimulus intensities, and smaller amplitude in BR’s right vs. left prefrontal sites. sLORETA analysis revealed that cortical responses were associated with a decreased activation of superior frontal gyrus and anterior cingulate cortex (BA 6/24). Interestingly, BR group only showed significant negative correlations between self-evaluation of painful intensities and frontal cortical negativity, revealing increasingly differentiated responses in bed rest: indeed those BR participants who reported lower pain ratings, displayed reduced negativity within anterior regions. Taken together, results indicate that short-term horizontal position is able to inhibit a fronto-parietal pain network, particularly at the level of central prefrontal regions typically involved in cognitive, affective and motor aspects of pain processing.

Posture affects emotional responses: a Head Down Bed Rest and ERP study

Body posture, mainly represented by horizontal bed rest, has been found to be associated with cortical inhibition, altered perceptual and cognitive processing. In the present research, the influence of Head Down Bed Rest (HDBR)--a condition also termed simulated microgravity--on emotional responses has been studied. Twenty-two male subjects were randomly assigned to either Sitting Control or HDBR group. After 3-h, subjects attended to a passive viewing emotional task in which 75 IAPS slides, divided into 25 pleasant, 25 neutral and 25 unpleasant, were presented in random order for 6s each, while EEG was recorded from F7, F8 and Pz locations. Results showed in Sitting Controls the expected greater P300 and Late Positive Potential (LPP) to pleasant and unpleasant compared with neutral slides, an effect which indicates greater processing of emotional arousing stimuli. The HDBR group showed smaller non-significant differences among all emotional conditions in both ERP components. Arousal and valence subjective evaluations, typically less sensitive to experimental manipulation, did not differentiate groups. The observed ability of HDBR to inhibit cortical emotional responses raises an important issue on the risk that astronauts underestimate a dangerous/threatening situation or that long-term bedridden inpatients develop depressive symptoms.

Event-related potential P2 correlates of implicit aesthetic experience

Using event-related potential measures, the present study investigated the affective responses to aesthetic experience. To differentiate the objective aesthetic value from subjective aesthetic evaluation, an amended oddball task was used in which pendant pictures were presented as frequent nontarget stimuli, whereas the landscape pictures were presented as a rare target. The pendant pictures were chosen from the largest online store in China and divided into beautiful and less beautiful conditions by the sales ranking. A positive component, P2, was recorded for each condition on the participants' frontal, central and parietal scalp areas. Less beautiful pendants elicited greater amplitudes of P2 than the beautiful ones. This indicates that emotion arousal seems to occur at the early stage of processing of aesthetics and can be detected by the P2 component, implying that the event-related potential methodology may be a more sensitive measure of the beauty-related attention bias. From the perspective of artwork design and marketing, our finding also shows that P2 can potentially be used as a reference measure in consumer aesthetic experience.

Orienting attention modulates pain perception: an ERP study

Introduction

Research has shown that people with chronic pain have difficulty directing their attention away from pain. A mental strategy that incorporates focused attention and distraction has been found to modulate the perception of pain intensity. That strategy involves placing attention on the nociceptive stimulus felt and shifting attention to a self-generated sub-nociceptive image and rehearsing it. Event-related potential was used to study the possible processes associated with the focus-then-orient strategy.

Methods

Eighteen pain-free participants received different levels of 50-ms nociceptive stimulations elicited by electric shocks at the right lateral malleolus (ankle). In perception trials, participants maintained the perceived nociceptive stimulus in working memory for 3,000 ms. In imagery trials, participants mentally generated and maintained the corresponding sub-nociceptive image they had learned previously. After both types of trials, participants evaluated the pain intensity of the incoming stimulus by recalling the feeling of the nociceptive stimulation at the beginning of the trial.

Results

Shifting attention from the incoming nociceptive to a self-generated sub-nociceptive image elicited central P2 and centro-parietal P3 waves, which were found to correlate with proportional scores on the Stroop Test. They were followed by a frontal N400 and a parietal P600, denoting generation of sub-nociceptive images in working memory. The voltages elicited in these potentials correlated moderately with attenuation of the pain ratings of the recalled nociceptive stimulations.

Conclusions

Focus-and-orient attention across nociceptive and sub-nociceptive images appears to be related to response inhibition. Mental rehearsal of the sub-nociceptive images was found to modulate the perception of the nociceptive sensation felt prior to the imagery. Such modulation seems to be mediated by generating and maintaining sub-nociceptive images in working memory. Future studies should explore the mental processes associated with orienting attention for pain modulation among people with pathological pain and frontal lobe dysfunction.