Focal changes in alpha oscillations during short-term memorization of pain: a high-density electroencephalogram study with source localization.

Memories of painful events constitute the basis for assessing patients' pain. This study explores the brain oscillatory activity during short-term memorization of a nociceptive stimulus. High-density EEG activity (128 electrodes) was recorded in 13 healthy subjects during a match-to-sample sensory discrimination task, whereby participants compared the intensity of a thumb-located electric shock (S2) with a prior stimulus to the same location (S1) delivered 8-10 s earlier.

Amygdala and anterior insula control the passage from nociception to pain.

Activation of the spinothalamic system does not always result in a subjective pain perception. While the cerebral network processing nociception is relatively well known, the one underlying its transition to conscious pain remains poorly described. We used intracranial electroencephalography in epileptic patients to investigate whether the amplitudes and functional connectivity of posterior and anterior insulae (PI and AI) and amygdala differ according to the subjective reports to laser stimuli delivered at a constant intensity set at nociceptive threshold.

Hyperalgesia when observing pain-related images is a genuine bias in perception and enhances autonomic responses.

Observing pain in others can enhance our own pain. Two aspects of this effect remain unknown or controversial: first, whether it depends on the 'painfulness' of the visual stimulus; second, whether it reflects a genuine bias in perception or rather a bias in the memory encoding of the percept. Pain ratings and vegetative skin responses were recorded while 21 healthy volunteers received electric nociceptive shocks under three experimental conditions: (i) observing a painful contact between the body and a harmful object; (ii) observing a non-painful body contact, (iii) observing a control scene where the body and the object are not in contact.

Cortical modulation of nociception by galvanic vestibular stimulation: A potential clinical tool?

Objective: Vestibular afferents converge with nociceptive ones within the posterior insula, and can therefore modulate nociception. Consistent with this hypothesis, caloric vestibular stimulation (CVS) has been shown to reduce experimental and clinical pain. Since CVS can induce undesirable effects in a proportion of patients, here we explored an alternative means to activate non-invasively the vestibular pathways using innocuous bi-mastoid galvanic stimulation (GVS), and assessed its effects on experimental pain.

Insular-limbic dissociation to intra-epidermal electrical Aδ activation: A comparative study with thermo-nociceptive laser stimulation.

Intra-epidermal electrical stimulation (IEES) has been shown to activate selectively Aδ fibers subserving spinothalamic-mediated sensations. Owing to electrically induced highly synchronous afferent volleys, IEES induces Aδ-mediated evoked potentials at nonpainful intensities, contrasting with thermo-nociceptive laser pulses which entail painful pricking sensations. Here, we recorded intracortical responses from sensory and limbic-cognitive regions of human subjects in response to IEE and laser stimuli, in order to test the hypothesis that IEES could dissociate the sensory from nonsensory networks of nociceptive processing.

Convergence of sensory and limbic noxious input into the anterior insula and the emergence of pain from nociception.

Two parallel di-synaptic routes convey nociceptive input to the telencephalon: the spino-thalamic system projecting principally to the posterior insula, and the spino-parabrachial pathway reaching the amygdalar nucleus. Interplay between the two systems underlies the sensory and emotional aspects of pain, and was explored here in humans with simultaneous recordings from the amygdala, posterior and anterior insulae. Onsets of thermo-nociceptive responses were virtually identical in the posterior insula and the amygdalar complex, but no significant functional connectivity was detected between them using coherence analysis.

A comprehensive literature review of chronic pain and memory.

Chronic pain patients often complain of their "poor memory" and numerous studies objectively confirmed such difficulties in reporting working memory (WM) and long-term memory (LTM) dysfunctions. This paper provides a comprehensive review of the literature on memory impairment in chronic pain (CP) patients. Twenty-four observational studies evaluating WM or/and LTM in a chronic pain group and a control group were included in this review.

Macroanatomy and 3D probabilistic atlas of the human insula.

The human insula is implicated in numerous functions. More and more neuroimaging studies focus on this region, however no atlas offers a complete subdivision of the insula in a reference space. The aims of this study were to define a protocol to subdivide insula, to create probability maps in the MNI152 stereotaxic space, and to provide normative reference volume measurements for these subdivisions.

Pain networks from the inside: Spatiotemporal analysis of brain responses leading from nociception to conscious perception.

Conscious perception of painful stimuli needs the contribution of an extensive cortico-subcortical network, and is completed in less than one second. While initial activities in operculo-insular and mid-cingulate cortices have been extensively assessed, the activation timing of most areas supporting conscious pain has barely been studied. Here we used intracranial EEG to investigate the dynamics of 16 brain regions (insular, parietal, prefrontal, cingulate, hippocampal and limbic) during the first second following nociceptive-specific laser pulses.

My Brain Reads Pain in Your Face, Before Knowing Your Gender.

Unlabelled: Humans are expert at recognizing facial features whether they are variable (emotions) or unchangeable (gender). Because of its huge communicative value, pain might be detected faster in faces than unchangeable features. Based on this assumption, we aimed to find a presentation time that enables subliminal discrimination of pain facial expression without permitting gender discrimination.

Thalamic Responses to Nociceptive-Specific Input in Humans: Functional Dichotomies and Thalamo-Cortical Connectivity.

While nociceptive cortical activation is now well characterized in humans, understanding of the nociceptive thalamus remains largely fragmentary. We used laser stimuli and intracerebral electrodes in 17 human subjects to record nociceptive-specific field responses in 4 human thalamic nuclei and a number of cortical areas. Three nuclei known to receive spinothalamic (STT) projections in primates (ventro-postero-lateral [VPL], anterior pulvinar [PuA], and central lateral [CL]) exhibited responses with similar latency, indicating their parallel activation by nociceptive afferents.

Processing of nociceptive input from posterior to anterior insula in humans.

Previous brain imaging studies have shown robust activations in the insula during nociceptive stimulation. Most activations involve the posterior insular cortex but they can cover all insular gyri in some fMRI studies. However, little is known about the timing of activations across the different insular sub-regions.

Asleep but aware?

Despite sleep-induced drastic decrease of self-awareness, human sleep allows some cognitive processing of external stimuli. Here we report the fortuitous observation in a patient who, while being recorded with intra-cerebral electrodes, was able, during paradoxical sleep, to reproduce a motor behaviour previously performed at wake to consciously indicate her perception of nociceptive stimulation. Noxious stimuli induced behavioural responses only if they reached the cortex during periods when mid-frontal networks (pre-SMA, pre-motor cortex) were pre-activated.

Cortical representation of pain in primary sensory-motor areas (S1/M1)--a study using intracortical recordings in humans.

Intracortical evoked potentials to nonnoxious Aβ (electrical) and noxious Aδ (laser) stimuli within the human primary somatosensory (S1) and motor (M1) areas were recorded from 71 electrode sites in 9 epileptic patients. All cortical sites responding to specific noxious inputs also responded to nonnoxious stimuli, while the reverse was not always true. Evoked responses in S1 area 3b were systematic for nonnoxious inputs, but seen in only half of cases after nociceptive stimulation.

Do we activate specifically somatosensory thin fibres with the concentric planar electrode? A scalp and intracranial EEG study.

Laser-evoked potentials (LEPs) are acknowledged as the most reliable laboratory tool for assessing thermal and pain pathways. Electrical stimulation with a newly developed planar concentric electrode, delivering stimuli limited to the superficial skin layers, has been suggested to provide selective activation of Aδ fibres without the inconveniences linked to laser stimulation. The aim of our study was to compare the scalp and intracranial responses to planar concentric electrode stimulation (CE-SEPs) with those of LEPs and standard somatosensory-evoked potentials (SEPs).

Filtering the reality: functional dissociation of lateral and medial pain systems during sleep in humans.

Behavioral reactions to sensory stimuli during sleep are scarce despite preservation of sizeable cortical responses. To further understand such dissociation, we recorded intracortical field potentials to painful laser pulses in humans during waking and all-night sleep. Recordings were obtained from the three cortical structures receiving 95% of the spinothalamic cortical input in primates, namely the parietal operculum, posterior insula, and mid-anterior cingulate cortex.

Evoked potentials to nociceptive stimuli delivered by CO2 or Nd:YAP lasers.

Objective: This study compares the amplitude, latency, morphology, scalp topography and intracranial generators of laser-evoked potentials (LEPs) to CO(2) and Nd:YAP laser stimuli.

Methods: LEPs were assessed in 11 healthy subjects (6 men, mean age 39+/-10 years) using a 32-channel acquisition system. Laser stimuli were delivered on the dorsum of both hands (intensity slightly above pain threshold), and permitted to obtain lateralised (N1) and vertex components (N2-P2) with similar scalp distribution for both types of lasers.

Pain influences hedonic assessment of visual inputs.

It is acknowledged that the emotional state created by visual inputs can modulate the way we feel pain; however, little is known about how acute pain influences the emotional assessment of what we see. In this study healthy subjects scored affective images while receiving painful or innocuous electrical shocks. Painful stimuli did not make unpleasant images more unpleasant, but rendered pleasant pictures significantly less pleasant.

Parallel processing of nociceptive A-delta inputs in SII and midcingulate cortex in humans.

The cingulate cortex (CC) as a part of the "medial" pain subsystem is generally assumed to be involved in the affective and/or cognitive dimensions of pain processing, which are viewed as relatively slow processes compared with the sensory-discriminative pain coding by the lateral second somatosensory area (SII)-insular cortex. The present study aimed at characterizing the location and timing of the CC evoked responses during the 1 s period after a painful laser stimulus, by exploring the whole rostrocaudal extent of this cortical area using intracortical recordings in humans. Only a restricted area in the median CC region responded to painful stimulation, namely the posterior midcingulate cortex (pMCC), the location of which is consistent with the so-called "motor CC" in monkeys.

Emotional modulation of pain: is it the sensation or what we recall?

Emotions modulate pain perception, although the mechanisms underlying this phenomenon remain unclear. In this study, we show that intensity reports significantly increased when painful stimuli were concomitant to images showing human pain, whereas pictures with identical emotional values but without somatic content failed to modulate pain. Early somatosensory responses (<200 ms) remained unmodified by emotions.

Human SII and posterior insula differently encode thermal laser stimuli.

The SII area and the posterior insular region are both activated by thermal stimuli in functional imaging studies. However, controversy remains as to a possible differential encoding of thermal intensity by each of these 2 contiguous areas. Using CO(2) laser stimulations, we analyzed the modifications induced by increasing thermal energy on evoked potentials recorded with electrodes implanted within SII and posterior insula in patients referred for presurgical evaluation of epilepsy.

Tonic, phasic, and integrator components of psychophysical responses to topical capsaicin account for differences of location and sex.

Unlabelled: We reanalyze data of Frot et al on sex and location differences in the pain response to topical capsaicin using a dynamic model developed from responses to oral capsaicin. This model considers the pain response as the sum of 3 underlying component processes: a phasic component, a tonic component, and an integrator component. Sex differences in response to stimulation of both the cheek and ankle could be accounted for by a greater gain in the tonic mechanism.

Thalamic thermo-algesic transmission: ventral posterior (VP) complex versus VMpo in the light of a thalamic infarct with central pain.

The respective roles of the ventral posterior complex (VP) and of the more recently described VMpo (posterior part of the ventral medial nucleus) as thalamic relays for pain and temperature pathways have recently been the subject of controversy. Data we obtained in one patient after a limited left thalamic infarct bring some new insights into this debate. This patient presented sudden right-sided hypesthesia for both lemniscal (touch, vibration, joint position) and spinothalamic (pain and temperature) modalities.

Sex differences in pain perception and anxiety. A psychophysical study with topical capsaicin.

Much evidence indicates that women experience painful stimuli as more intense than men do. Nevertheless, some data suggest that sustained low-level pain may be more disturbing to men than to women. The current experiment evaluated the hypothesis that pain is more disturbing for men than for women by comparing across genders sensory and emotional aspects of pain evoked by capsaicin.