Expectancy of Pain Is Influenced by Motor Preparation: A High-Resolution EEG Study of Cortical Alpha Rhythms

Temporal structure of brain oscillations predicts learned nocebo responses to pain

This study aimed to identify electrophysiological correlates of nocebo-augmented pain. Nocebo hyperalgesia (i.e., increases in perceived pain resulting from negative expectations) has been found to impact how healthy and patient populations experience pain and is a phenomenon that could be better understood in terms of its neurophysiological underpinnings. In this study, nocebo hyperalgesia was induced in 36 healthy participants through classical conditioning and negative suggestions. Electroencephalography was recorded during rest (pre- and post-acquisition) and during pain stimulation (baseline, acquisition, evocation) First, participants received baseline high thermal pain stimulations. During nocebo acquisition, participants learned to associate an inert gel applied to their forearm with administered high pain stimuli, relative to moderate intensity control stimuli administered without gel. During evocation, all stimuli were accompanied by moderate pain, to measure nocebo responses to the inert gel. Pre- to post-acquisition beta-band alterations in long-range temporal correlations (LRTC) were negatively associated with nocebo magnitudes. Individuals with strong resting LRTC showed larger nocebo responses than those with weaker LRTC. Nocebo acquisition trials showed reduced alpha power. Alpha power was higher while LRTC were lower during nocebo-augmented pain, compared to baseline. These findings support nocebo learning theories and highlight a role of nocebo-induced cognitive processing.

Tonic thermonociceptive stimulation selectively modulates ongoing neural oscillations in the human posterior insula: Evidence from intracerebral EEG

The human insula is an important target for spinothalamic input, but there is still no consensus on its role in pain perception and nociception. In this study, we show that the human insula exhibits activity preferential for sustained thermonociception. Using intracerebral EEG recorded from the insula of 8 patients (2 females) undergoing a presurgical evaluation of focal epilepsy (53 contacts: 27 anterior, 26 posterior), we "frequency-tagged" the insular activity elicited by sustained thermonociceptive and vibrotactile stimuli, by periodically modulating stimulation intensity at a fixed frequency of 0.2 Hz during 75 s. Both types of stimuli elicited an insular response at the frequency of stimulation (0.2 Hz) and its harmonics, whose magnitude was significantly greater in the posterior insula compared to the anterior insula. Compared to vibrotactile stimulation, thermonociceptive stimulation exerted a markedly greater 0.2 Hz modulation of ongoing theta-band (4-8 Hz) and alpha-band (8-12 Hz) oscillations. These modulations were also more prominent in the posterior insula compared to the anterior insula. The identification of oscillatory activities preferential for thermonociception could lead to new insights into the physiological mechanisms of nociception and pain perception in humans.

Differential Neural Processing during Motor Imagery of Daily Activities in Chronic Low Back Pain Patients

Chronic low back pain (chronic LBP) is both debilitating for patients but also a major burden on the health care system. Previous studies reported various maladaptive structural and functional changes among chronic LBP patients on spine- and supraspinal levels including behavioral alterations. However, evidence for cortical reorganization in the sensorimotor system of chronic LBP patients is scarce. Motor Imagery (MI) is suitable for investigating the cortical sensorimotor network as it serves as a proxy for motor execution. Our aim was to investigate differential MI-driven cortical processing in chronic LBP compared to healthy controls (HC) by means of functional magnetic resonance imaging (fMRI). Twenty-nine subjects (15 chronic LBP patients, 14 HC) were included in the current study. MI stimuli consisted of randomly presented video clips showing every-day activities involving different whole-body movements as well as walking on even ground and walking downstairs and upstairs. Guided by the video clips, subjects had to perform MI of these activities, subsequently rating the vividness of their MI performance. Brain activity analysis revealed that chronic LBP patients exhibited significantly reduced activity compared to HC subjects in MI-related brain regions, namely the left supplementary motor area and right superior temporal sulcus. Furthermore, psycho-physiological-interaction analysis yielded significantly enhanced functional connectivity (FC) between various MI-associated brain regions in chronic LBP patients indicating diffuse and non-specific changes in FC. Current results demonstrate initial findings about differences in MI-driven cortical processing in chronic LBP pointing towards reorganization processes in the sensorimotor network.

Subjective pain perception mediated by alpha rhythms

Suppression of spontaneous alpha oscillatory activities, interpreted as cortical excitability, was observed in response to both transient and tonic painful stimuli. The changes of alpha rhythms induced by pain could be modulated by painful sensory inputs, experimental tasks, and top-down cognitive regulations such as attention. The temporal and spatial characteristics, as well as neural functions of pain induced alpha responses, depend much on how these factors contribute to the observed alpha event-related desynchronization/synchronization (ERD/ERS). How sensory-, task-, and cognitive-related changes of alpha oscillatory activities interact in pain perception process is reviewed in the current study, and the following conclusions are made: (1) the functional inhibition hypothesis that has been proposed in auditory and visual modalities could be applied also in pain modality; (2) the neural functions of pain induced alpha ERD/ERS were highly dependent on the cortical regions where it is observed, e.g., somatosensory cortex alpha ERD/ERS in pain perception for painful stimulus processing; (3) the attention modulation of pain perception, i.e., influences on the sensory and affective dimensions of pain experience, could be mediated by changes of alpha rhythms. Finally, we propose a model regarding the determinants of pain related alpha oscillatory activity, i.e., sensory-discriminative, affective-motivational, and cognitive-modulative aspects of pain experience, would affect and determine pain related alpha oscillatory activities in an integrated way within the distributed alpha system.

Cortical EEG alpha rhythms reflect task-specific somatosensory and motor interactions in humans

Anticipating sensorimotor events allows adaptive reactions to environment with crucial implications for self-protection and survival. Here we review several studies of our group that aimed to test the hypothesis that the cortical processes preparing the elaboration of sensorimotor interaction is reflected by the reduction of anticipatory electroencephalographic alpha power (about 8-12Hz; event-related desynchronization, ERD), as an index that regulate task-specific sensorimotor processes, accounted by high-alpha sub-band (10-12Hz), rather than a general tonic alertness, accounted by low-alpha sub-band (8-10Hz). In this line, we propose a model for human cortical processes anticipating warned sensorimotor interactions. Overall, we reported a stronger high-alpha ERD before painful than non-painful somatosensory stimuli that is also predictive of the subjective evaluation of pain intensity. Furthermore, we showed that anticipatory high-alpha ERD increased before sensorimotor interactions between non-painful or painful stimuli and motor demands involving opposite hands. In contrast, sensorimotor interactions between painful somatosensory and sensorimotor demands involving the same hand decreased anticipatory high-alpha ERD, due to a sort of sensorimotor "gating" effect. In conclusion, we suggest that anticipatory cortical high-alpha rhythms reflect the central interference and/or integration of ascending (sensory) and descending (motor) signals relative to one or two hands before non-painful and painful sensorimotor interactions.

Spectral signatures of viewing a needle approaching one's body when anticipating pain

When viewing the needle of a syringe approaching your skin, anticipation of a painful prick may lead to increased arousal. How this anticipation is reflected in neural oscillatory activity and how it relates to activity within the autonomic nervous system is thus far unknown. Recently, we found that viewing needle pricks compared with Q-tip touches increases the pupil dilation response (PDR) and perceived unpleasantness of electrical stimuli. Here, we used high-density electroencephalography to investigate whether anticipatory oscillatory activity predicts the unpleasantness of electrical stimuli and PDR while viewing a needle approaching a hand that is perceived as one's own. We presented video clips of needle pricks and Q-tip touches, and delivered spatiotemporally aligned painful and nonpainful intracutaneous electrical stimuli. The perceived unpleasantness of electrical stimuli and the PDR were enhanced when participants viewed needle pricks compared with Q-tip touches. Source reconstruction using linear beamforming revealed reduced alpha-band activity in the posterior cingulate cortex (PCC) and fusiform gyrus before the onset of electrical stimuli when participants viewed needle pricks compared with Q-tip touches. Moreover, alpha-band activity in the PCC predicted PDR on a single trial level. The anticipatory reduction of alpha-band activity in the PCC may reflect a neural mechanism that serves to protect the body from forthcoming harm by facilitating the preparation of adequate defense responses.

Asymmetric cortical adaptation effects during alternating auditory stimulation

The present study investigates hemispheric asymmetries in the neural adaptation processes occurring during alternating auditory stimulation. Stimuli were two monaural pure tones having a frequency of 400 or 800 Hz and a duration of 500 ms. Electroencephalogram (EEG) was recorded from 14 volunteers during the presentation of the following stimulus sequences, lasting 12 s each: 1) evoked potentials (EP condition, control), 2) alternation of frequency and ear (FE condition), 3) alternation of frequency (F condition), and 4) alternation of ear (E condition). Main results showed that in the central area of the left hemisphere (around C3 site) the N100 response underwent adaptation in all patterns of alternation, whereas in the same area of the right hemisphere the tones presented at the right ear in the FE produced no adaptation. Moreover, the responses to right-ear stimuli showed a difference between hemispheres in the E condition, which produced less adaptation in the left hemisphere. These effects are discussed in terms of lateral symmetry as a product of hemispheric, pathway and ear asymmetries.

Neural correlates of cognitive ability

The challenge to neuroscientists working on intelligence is to discover what neural structures and mechanisms are at the basis of such a complex and variegated capability. Several psychologists agree on the view that behavioral flexibility is a good measure of intelligence, resulting in the appearance of novel solutions that are not part of the animal's normal behavior. This article tries to indicate how the supposed differences in intelligence between species can be related to brain properties and suggests that the best neural indicators may be the ones that convey more information processing capacity to the brain, i.e., high conduction velocity of fibers and small distances between neurons, associated with a high number of neurons and an adequate level of connectivity. The neural bases of human intelligence have been investigated by means of anatomical, neurophysiological, and neuropsychological methods. These investigations have led to two important findings that are briefly discussed: the parietofrontal integration theory of intelligence, which assumes that a distributed network of cortical areas having its main nodes in the frontal and parietal lobes constitutes a probable substrate for smart behavior, and the neural efficiency hypothesis, according to which intelligent people process information more efficiently, showing weaker neural activations in a smaller number of areas than less intelligent people.

An extension of the functional cerebral systems approach to hostility: a capacity model utilizing a dual concurrent task paradigm

Regulatory control of emotions and expressive fluency (verbal or design) have historically been associated with the frontal lobes. Moreover, research has demonstrated the importance of cerebral laterality with a prominent role of the right frontal regions in the regulation of negative affect (anger, hostility) and in the fluent production of designs rather than verbal fluency. In the present research, participants identified with high and with low levels of hostility were evaluated on a design fluency test twice in one experimental session. Before the second administration of the fluency test, each participant underwent physiological (cold pressor) stress. It was hypothesized that diminished right frontal capacity in high-hostile men would be evident through lowered performance on this cognitive stressor. Convergent validity of the capacity model was supported wherein high-hostile men evidenced reduced delta magnitude over the right frontal region after exposure to the physiological stressor but failed to maintain consistent levels of right cerebral activation across conditions. The results suggest an inability for high-hostile men to maintain stable levels of cerebral activation after exposure to physiological and cognitive stress. Moreover, low-hostiles showed enhanced cognitive performance on the design task with lower levels of arousal (heightened delta magnitude). In contrast, reduced arousal yielded increased executive deficits in high-hostiles as evidenced through increased perseverative errors on the design fluency task.

Low back pain associates with altered activity of the cerebral cortex prior to arm movements that require postural adjustment

OBJECTIVE

To determine whether low back pain (LBP) associates with altered postural stabilization and concomitant changes in cerebrocortical motor physiology.

METHODS

Ten participants with LBP and 10 participants without LBP performed self-initiated, voluntary arm raises. Electromyographic onset latencies of the bilateral internal oblique and erector spinae muscles were analyzed relative to that of the deltoid muscle as measures of anticipatory postural adjustments (APAs). Amplitudes of alpha event-related desynchronization (ERD) and of Bereitschaftspotentials (BP) were calculated from scalp electroencephalography as measures of cerebrocortical motor physiology.

RESULTS

The APA was first evident in the trunk muscles contralateral to the arm raise for both groups. Significant alpha ERD was evident bilaterally at the central and parietal electrodes for participants with LBP but only at the electrodes contralateral and midline to the arm raise for those without LBP. The BP amplitudes negatively correlated with APA onset latencies for participants with (but not for those without) LBP.

CONCLUSIONS

Cerebrocortical activity becomes altered prior to arm movements requiring APAs for individuals with chronic LBP.

SIGNIFICANCE

These results support a theoretical model that altered central motor neurophysiology associates with LBP, thereby implying that rehabilitation strategies should address these neuromotor impairments.

Abnormal neural reactivity to unpredictable sensory events in attention-deficit/hyperactivity disorder

BACKGROUND

Cortical oscillations in the sensorimotor region in the 8-12-Hz range ("mu rhythms") are associated with basic somatosensory and motor processes as well as top-down processes such as learning, attention, expectancy, and inhibition. Recent studies suggest that reactivity of these rhythms to sensory input reflects a link between perception and action and that abnormalities in this reactivity might reflect impairment in perception-to-action mechanisms. Individuals with attention-deficit/hyperactivity disorder (ADHD) are impaired in tasks requiring sensorimotor function, attention, expectancy, and inhibition, yet their sensorimotor mu responses are unknown. Thus, we investigated mu reactivity in a group of adults with ADHD.

METHODS

Sixteen adults with ADHD and 16 matched control subjects received median nerve stimulation in predictable patterns (trains of four stimuli followed by 4-sec gap) or unpredictable patterns (randomly presented trains of two, four, or six stimuli followed by 4-sec gap). With magnetoencephalography, we examined the effects of stimulus patterning (predictable, unpredictable) on mu reactivity to somatosensory stimuli.

RESULTS

Compared with control subjects, the ADHD group showed lower mu reactivity overall and no modulation by unpredictable somatosensory input. By contrast, the control group showed robust mu reactivity to stimuli presented in unpredictable but not predictable patterns. These changes were stronger in the contralateral hemisphere compared with the ADHD group.

CONCLUSIONS

Cortical mu rhythms are modulated by stimulus predictability and might be involved in attentional alerting (awareness of when an unexpected stimulus occurs). Diminished mu modulation in adult ADHD suggests a possible underlying deficit in the perception-to-action system.

EEG indices of tonic pain-related activity in the somatosensory cortices

OBJECTIVE

To identify EEG features that index pain-related cortical activity, and to identify factors that can mask the pain-related EEG features and/or produce features that can be misinterpreted as pain-specific.

METHODS

The EEG was recorded during three conditions presented in counterbalanced order: a tonic cold pain condition, and pain anticipation and arithmetic control conditions. The EEG was also recorded while the subjects made a wincing facial expression to estimate the contribution of scalp EMG artifacts to the pain-related EEG features.

RESULTS

Alpha amplitudes decreased over the contralateral temporal scalp and increased over the posterior scalp during the cold pain condition. There was an increase in gamma band activity during the cold pain condition at most electrode locations that was due to EMG artifacts.

CONCLUSIONS

The decrease in alpha over the contralateral temporal scalp during cold pain is consistent with pain-related activity in the primary somatosensory cortex and/or the somatosensory association areas located in the parietal operculum and/or insula. This study also identified factors that might mask the pain-related EEG features and/or generate EEG features that could be misinterpreted as being pain-specific. These include (but are not limited to) an increase in alpha generated in the visual cortex that results from attention being drawn towards the pain; the widespread increase in gamma band activity that results from scalp EMG generated by the facial expressions that often accompany pain; and the possibility that non-specific changes in the EEG over time mask the pain-related EEG features when the pain and control conditions are given in the same order across subjects.

SIGNIFICANCE

This study identified several factors that need to be controlled and/or isolated in order to successfully record EEG features that index pain-related activity in the somatosensory cortices.

Pre-stimulus alpha power affects vertex N2-P2 potentials evoked by noxious stimuli

It is well known that scalp potentials evoked by nonpainful visual and auditory stimuli are enhanced in amplitude when preceded by pre-stimulus low-amplitude alpha rhythms. This study tested the hypothesis that the same holds for the amplitude of vertex N2-P2 potentials evoked by brief noxious laser stimuli, an issue of interest for clinical perspective. EEG data were recorded in 10 subjects from 30 electrodes during laser noxious stimulation. The artifact-free vertex N2-P2 complex was spatially enhanced by surface Laplacian transformation. Pre-stimulus alpha power was computed at three alpha sub-bands according to subject's individual alpha frequency peak (i.e. about 6-8Hz for alpha 1, 8-10Hz for alpha 2 and 10-12Hz for alpha 3 sub-band). Individual EEG single trials were divided in two sub-groups. The strong-alpha sub-group (high band power) included halfway of all EEG single trials, namely those having the highest pre-stimulus alpha power. Weak-alpha sub-group (low band power) included the remaining trials. Averaging procedure provided laser evoked potentials for both trial sub-groups. No significant effect was found for alpha 1 and alpha 2 sub-bands. Conversely, compared to strong-alpha 3 sub-group, weak-alpha 3 sub-group showed vertex N2-P2 potentials having significantly higher amplitude (p<0.05). These results extend to the later phases of pain processing systems the notion that generation mechanisms of pre-stimulus alpha rhythms and (laser) evoked potentials are intrinsically related and subjected to fluctuating "noise". That "noise" could explain the trial-by-trial variability of laser evoked potentials and perception.

Cortical alpha rhythms are correlated with body sway during quiet open-eyes standing in athletes: A high-resolution EEG study

Electroencephalographic (EEG; Be-plus Eb-Neuro) and stabilogram (RGM) data were simultaneously recorded in 19 elite karate and 18 fencing athletes and in 10 non-athletes during quiet upright standing at open- and closed-eyes condition in order to investigate the correlation between cortical activity and body sway when the visual inputs are available for balance. Our working hypothesis is that, at difference of non-athletes, athletes are characterized by enhanced cortical information processing as indexed by the amplitude reduction of EEG oscillations at alpha rhythms (about 8-12 Hz) during open- referenced to closed-eyes condition (event-related desynchronization, ERD). Balance during quiet standing was indexed by body "sway area". Correlation between alpha ERD and event-related change of the sway area was computed by a non-parametric test (p<0.05). It was found that alpha ERD (10-12 Hz) is stronger in amplitude in the karate and fencing athletes than in the non-athletes at ventral centro-parietal electrodes of the right hemisphere (p<0.02). Furthermore, there was a statistically significant correlation in the karate athletes between right ventral centro-parietal alpha ERD and body sway area (r=0.61; p<0.008): specifically, the greater the alpha ERD, the greater the percentage reduction of the body sway area when the visual inputs were available. These results suggest that parasylvian alpha ERD of the right hemisphere may reflect the cortical information processing for the balance in elite athletes subjected to a long training for equilibrium control.

Different modalities of painful somatosensory stimulations affect anticipatory cortical processes: A high-resolution EEG study

Pain sensation is characterized by multiple features that allow to differentiate pricking, burning, aching, stinging, and electrical shock. These features are sub-served by neural pathways that might give flexibility and selectivity to the cerebral anticipatory processes. In this line, the present high-resolution electroencephalography (EEG) study tested the hypothesis that the anticipatory cortical processes are stronger for painful thermal (biologically relevant) than electrical ("artificial") stimuli with similar intensity. EEG data (128 electrodes) were recorded in normal subjects during the expectancy of painful electrical or laser stimuli (visual omitted stimulus paradigm; interval between two painful stimuli: 16s), delivered over the median nerve region of the right arm (nonpainful stimuli as controls). After each stimulus, the subject reported the perceived stimulus intensity. Surface Laplacian estimation of the EEG data spatially enhanced the anticipatory stimulus-preceding negativity (SPN), which reflects motivational relevance of the stimulus. Subjects perceived no difference in the intensity of the electrical versus laser stimuli in both painful and nonpainful conditions. However, the anticipatory SPN appeared over large scalp regions before painful laser but not electrical stimulation. The same was true for the nonpainful stimulations. The present results suggest that the motivational anticipatory cortical processes are induced by nonpainful and painful biologically/ecologically relevant laser stimuli rather than by "artificial" electrical stimuli with similar intensity.

Anticipatory electroencephalography alpha rhythm predicts subjective perception of pain intensity

This high-resolution electroencephalography (EEG) study tested the hypothesis that the suppression of rolandic alpha power before predictable painful stimulation affects the subject's subsequent evaluation of pain intensity, as a reflection of the influence of expectancy processes on painful stimulus processing. High-resolution EEG data were recorded (126 channels) from 10 healthy adult volunteers during the expectancy of a painful CO(2)-laser stimulation at the right wrist. Surface laplacian estimation enhanced the EEG spatial information content over 6 scalp regions of interest (left frontal, right frontal, left central, right central, left parietal, and right parietal areas). Spectral power was computed for 3 alpha sub-bands with reference to the individual alpha frequency peak (about 5-7 Hz for alpha 1, 7-9 Hz for alpha 2, and 9-11 Hz for alpha 3). The suppression of the alpha power before the painful stimulation [as reflected by the event-related desynchronization (ERD)] indexed the anticipatory cortical processes. Results showed maximum (negative) correlations between the alpha 2 and alpha 3 ERD amplitude at the left central area and the subjective evaluation of pain intensity (P < .001). The stronger the anticipatory alpha 2 and alpha 3 ERD, the higher the subjective evaluation of pain intensity. For alpha 3, that correlation was confirmed even when the effect of habituation across the recording session was taken into account. These results suggest that the anticipatory suppression of the alpha rhythms over the contralateral primary sensorimotor cortex predicts subsequent subjects' evaluation of pain intensity, in line with its crucial role for the discrimination of that intensity.

PERSPECTIVE

This electroencephalographic study showed that anticipatory activation/deactivation of sensorimotor cortex roughly predicts subjective evaluation of pain. This motivates further investigation on possible implications for the understanding of central chronic pain. Chronic pain patients might exaggerate the anticipatory activation of sensorimotor cortex to negligible pain stimuli.

Cortical oscillatory changes occurring during somatosensory and thermal stimulation

Brief somatosensory stimuli are followed by amplitude decreases (event-related desynchronization, ERD) of the 10 and 20 Hz oscillations over the bilateral primary sensorimotor cortices, and by post-stimulus synchronization (event-related synchronization, ERS) of the 20 Hz oscillations in the contralateral primary sensorimotor cortex and in the supplementary motor area (SMA). The 10 and 20 Hz ERD differentiate weak and strong somatosensory stimuli but not fine intensity gradations, and the ipsilateral ERD is especially sensitive to habituation. Stimulus anticipation, motor imagery, action viewing as well as voluntary movements modulate the stimulus-related changes of cortical oscillations. Noxious laser stimuli, selectively activating Adelta and/or C fibers, and innocuous warm and cold stimuli are associated with 10 and 20 Hz ERD but not with the post-stimulus 20 Hz ERS suggesting that the post-stimulus ERS is only related to neuronal transmission in the lemniscal system. It is proposed that phase-unlocked cortical oscillations modulate the preparedness of a particular sensory channel for upcoming somatosensory processing.