Cortical representation of pain

Extraction and Analysis of Dynamic Functional Connectome Patterns in Migraine Sufferers: A Resting-State fMRI Study

Migraine seriously affects the physical and mental health of patients because of its recurrence and the hypersensitivity to the environment that it causes. However, the pathogenesis and pathophysiology of migraine are not fully understood. We addressed this issue in the present study using an autodynamic functional connectome model (A-DFCM) with twice-clustering to compare dynamic functional connectome patterns (DFCPs) from resting-state functional magnetic resonance imaging data from migraine patients and normal control subjects. We used automatic localization of segment points to improve the efficiency of the model, and intergroup differences and network metrics were analyzed to identify the neural mechanisms of migraine. Using the A-DFCM model, we identified 17 DFCPs-including 1 that was specific and 16 that were general-based on intergroup differences. The specific DFCP was closely associated with neuronal dysfunction in migraine, whereas the general DFCPs showed that the 2 groups had similar functional topology as well as differences in the brain resting state. An analysis of network metrics revealed the critical brain regions in the specific DFCP; these were not only distributed in brain areas related to pain such as Brodmann area 1/2/3, basal ganglia, and thalamus but also located in regions that have been implicated in migraine symptoms such as the occipital lobe. An analysis of the dissimilarities in general DFCPs between the 2 groups identified 6 brain areas belonging to the so-called pain matrix. Our findings provide insight into the neural mechanisms of migraine while also identifying neuroimaging biomarkers that can aid in the diagnosis or monitoring of migraine patients.

Critical aspects of neurodevelopment

Organisms have the unique ability to adapt to their environment by making use of external inputs. In the process, the brain is shaped by experiences that go hand-in-hand with optimisation of neural circuits. As such, there exists a time window for the development of different brain regions, each unique for a particular sensory modality, wherein the propensity of forming strong, irreversible connections are high, referred to as a critical period of development. Over the years, this domain of neurodevelopmental research has garnered considerable attention from many scientists, primarily because of the intensive activity-dependent nature of development. This review discusses the cellular, molecular, and neurophysiological bases of critical periods of different sensory modalities, and the disorders associated in cases the regulators of development are dysfunctional. Eventually, the neurobiological bases of the behavioural abnormalities related to developmental pathologies are discussed. A more in-depth insight into the development of the brain during the critical period of plasticity will eventually aid in developing potential therapeutics for several neurodevelopmental disorders that are categorised under critical period disorders.

The Contribution of Thalamic Nuclei in Salience Processing

The brain continuously receives diverse information about the external environment and changes in the homeostatic state. The attribution of salience determines which stimuli capture attention and, therefore, plays an essential role in regulating emotions and guiding behaviors. Although the thalamus is included in the salience network, the neural mechanism of how the thalamus contributes to salience processing remains elusive. In this mini-review, we will focus on recent advances in understanding the specific roles of distinct thalamic nuclei in salience processing. We will summarize the functional connections between thalamus nuclei and other key nodes in the salience network. We will highlight the convergence of neural circuits involved in reward and pain processing, arousal, and attention control in thalamic structures. We will discuss how thalamic activities represent salience information in associative learning and how thalamic neurons modulate adaptive behaviors. Lastly, we will review recent studies which investigate the contribution of thalamic dysfunction to aberrant salience processing in neuropsychiatric disorders, such as drug addiction, posttraumatic stress disorder (PTSD), and schizophrenia. Based on emerging evidence from both human and rodent research, we propose that the thalamus, different from previous studies that as an information relay, has a broader role in coordinating the cognitive process and regulating emotions.

Chronic Pain is Associated with Deficits in Information Processing

Beginning with the theoretical premise that pain stimuli are liable to perturb the ordinary dynamical state of the brain, we hypothesized that individuals in pain may experience impaired information processing. A sample of 19 persons complaining of chronic pain and a comparison sample of 25 persons having sustained head trauma were obtained by retrospective chart review. The chronic-pain group consisted of 19 persons whose primary complaint was significant chronic pain, with no known history of head trauma or neurologic disorder. The comparison group consisted of 25 persons who had sustained mild to moderate head traumas. All subjects were administered information processing and motor subtests of the Human Performance Measurement System, a computerized set of measures. Both groups obtained mean z scores below the normative mean on all measures except visual digit span. There were no differences between groups on motor measures, visual digit span, and visual-spatial memory. On 2 of 6 information-processing tests, pain patients performed more poorly than head-trauma patients. The results suggest that pain may disrupt cognitive performances which depend on intact speed and capacity of information processing.

Characterization of obstacle negotiation behaviors in the cockroach, Blaberus discoidalis

Within natural environments, animals must be able to respond to a wide range of obstacles in their path. Such responses require sensory information to facilitate appropriate and effective motor behaviors. The objective of this study was to characterize sensors involved in the complex control of obstacle negotiation behaviors in the cockroach Blaberus discoidalis. Previous studies suggest that antennae are involved in obstacle detection and negotiation behaviors. During climbing attempts, cockroaches swing their front leg that then either successfully reaches the top of the block or misses. The success of these climbing attempts was dependent on their distance from the obstacle. Cockroaches with shortened antennae were closer to the obstacle prior to climbing than controls, suggesting that distance was related to antennal length. Removing the antennal flagellum resulted in delays in obstacle detection and changes in climbing strategy from targeted limb movements to less directed attempts. A more complex scenario – a shelf that the cockroach could either climb over or tunnel under – allowed us to further examine the role of sensory involvement in path selection. Ultimately, antennae contacting the top of the shelf led to climbing whereas contact on the underside led to tunneling However, in the light, cockroaches were biased toward tunnelling; a bias which was absent in the dark. Selective covering of visual structures suggested that this context was determined by the ocelli.

Cerebral representation of the anorectum using functional magnetic resonance imaging

BACKGROUND

Anorectal continence depends not only on the organs of continence but also on cerebral control. There are relatively few data regarding cerebral processing of anorectal continence.

METHODS

Thirteen healthy subjects underwent rectal distension to cause urge increasing to discomfort during functional magnetic resonance imaging (fMRI). In addition, a painful heat stimulus was applied to the skin of the anterior abdominal wall in the dermatome corresponding to the rectum. Voluntary contraction of the anal sphincter was also performed. Subjective rating of stimulus intensity was recorded. Evaluation of the data used a general linear model with Brain Voyager(trade mark).

RESULTS

Subjective sensation of discomfort increased during repeated rectal distension and caused activation in the anterior cingulate gyrus, insula, thalamus and secondary somatosensory cortex seen on fMRI. Perception of rectal urge and discomfort activated the same cerebral regions with differing intensity. Application of a painful thermal stimulus in the corresponding dermatome showed a modification of the response. Voluntary contraction of the anal sphincter led to activation of the motor cortex and increased activity in the supplementary motor cortex and the insula.

CONCLUSION

Cerebral representation of the anorectum as mapped by fMRI is intricate and reflects the complexity of the continence mechanism.

Differentiating noxious- and innocuous-related activation of human somatosensory cortices using temporal analysis of fMRI

The role of the somatosensory cortices (SI and SII) in pain perception has long been in dispute. Human imaging studies demonstrate activation of SI and SII associated with painful stimuli, but results have been variable, and the functional relevance of any such activation is uncertain. The present study addresses this issue by testing whether the time course of somatosensory activation, evoked by painful heat and nonpainful tactile stimuli, is sufficient to discriminate temporal differences that characterize the perception of these stimulus modalities. Four normal subjects each participated in three functional magnetic resonance imaging (fMRI) sessions, in which painful (noxious heat 45-46 degrees C) and nonpainful test stimuli (brushing at 2 Hz) were applied repeatedly (9-s stimulus duration) to the left leg in separate experiments. Activation maps were generated comparing painful to neutral heat (35 degrees C) and nonpainful brushing to rest. Directed searches were performed in SI and SII for sites reliably activated by noxious heat and brush stimuli, and stimulus-dependent regions of interest (ROI) were then constructed for each subject. The time course, per stimulus cycle, was extracted from these ROIs and compared across subjects, stimulus modalities, and cortical regions. Both innocuous brushing and noxious heat produced significant activation within contralateral SI and SII. The time course of brush-evoked responses revealed a consistent single peak of activity, approximately 10 s after the onset of the stimulus, which rapidly diminished upon stimulus withdrawal. In contrast, the response to heat pain in both SI and SII was characterized by a double-peaked time course in which the maximum response (the 2nd peak) was consistently observed approximately 17 s after the onset of the stimulus (8 s following termination of the stimulus). This prolonged period of activation paralleled the perception of increasing pain intensity that persists even after stimulus offset. On the other hand, the temporal profile of the initial minor peak in pain-related activation closely matched that of the brush-evoked activity, suggesting a possible relationship to tactile components of the thermal stimulation procedure. These data indicate that both SI and SII cortices are involved in the processing of nociceptive information and are consistent with a role for these structures in the perception of temporal aspects of pain intensity.

Cortical mapping of visceral pain in patients with GI disorders using functional magnetic resonance imaging

OBJECTIVE

We sought to identify central loci that activate in response to visceral stimuli (stool and pain). We had a particular interest in observing the anterior cingulate gyrus and frontal cortex in normals and in patients with intestinal disease, including inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS).

METHODS

Subjects underwent rectal balloon distention to a sensation of stool and to a sensation of pain while undergoing blood oxygenation level-dependent functional magnetic resonance imaging. Experiments were conducted in a Magnex 3.0-T whole body magnet with a Bruker Biospec console and a quadrature head coil. Four contiguous 5.0-mm oblique axial slices designed to optimize coverage of areas believed to be responsive to noxious stimulation were acquired. Activations were detected by using cross-correlation maps (p < 0.001) for individual subjects. The experimental groups were compared using both an analysis of variance and profile analysis.

RESULTS

A significantly higher percentage of pixels activated in the anterior cingulate gyrus over both pain and stool conditions for the control group than for the IBS group and for the IBS group than for the IBD group (p < 0.035). Deactivation of left somatosensory cortex was greater for the IBS group than for the IBD group and greater for the IBD group than for the controls (p < 0.0065) in the boxcar condition. Frontal deactivation in controls compared with disease groups bordered on statistical significance. Profile analysis of the three groups across six regions of interest revealed that the control and IBD groups were distinguished by different profiles of response (p < 0.005). Nonparametric evaluation of the data suggests that, among the pixels in the anterior cingulate activating to pain, there are two patterns of response to pain-on/off and graded. This was true for both controls and disease groups.

CONCLUSIONS

Normal controls and subjects with IBD and IBS share similar loci of activations to visceral sensations of stool and pain. Both activation and deactivation of particular regions of interest differentiate the three groups, as do profiles of patterned response across six of the regions of interest for the control and IBD groups.

Functional MR imaging of regional brain activation associated with the affective experience of pain

OBJECTIVE

Current models propose that the experience of pain includes both sensory and affective components. Our purpose was to use functional MR imaging to determine areas of the brain engaged by the affective dimension of pain.

SUBJECTS AND METHODS

Twelve healthy adults underwent functional MR imaging using a gradient-echo echoplanar technique while a cold pressor test, consisting of cold and pain tasks, was applied first to one foot and then to the other. The cold task involved the application of cold water (14-20 degrees C) that was not at a painful level. For the pain task, the water temperature was then lowered to a painful temperature (8-14 degrees C) and subsequently to the pain threshold (3-8 degrees C). Images acquired at room temperature before the cold and pain tasks served as a baseline task. Composite maps of brain activation were generated by comparing the baseline task with the cold task and the cold task with the pain task. The significance of signal changes was estimated by randomization of individual activation maps.

RESULTS

Cold-related activation (p < 0.01) was found in the postcentral gyrus bilaterally, laterally, and inferiorly to the primary motor-sensory area of the foot and at a site near the second somatosensory site. Activation also occurred in the frontal lobe (the bilateral middle frontal gyri and the right inferior frontal gyrus), the left anterior insula, the left thalamus, and the superior aspect of the anterior cingulate gyrus (seen at one slice location). Pain-related activation (p < 0.01) included the anterior cingulate gyrus (seen at four slice locations); the superior frontal gyrus, especially on the right; and the right cuneus.

CONCLUSION

Compared with the basic sensory processing of pain, the affective dimension of pain activates a cortical network that includes the right superior frontal gyrus, the right cuneus, and a large area of the anterior cingulate gyrus.

Cerebral blood-flow changes evoked by two levels of painful heat stimulation: a positron emission tomography study in humans

Positron emission tomography (PET) and accumulation of H(2)(15)O as a marker of neuronal activity were used to create maps of cerebral blood-flow changes evoked by painful heat stimulation in 10 subjects. Two levels of painful tonic and phasic heat stimuli were applied with use of a newly developed contact heat thermode on the volar surface of the dominant (right) arm. The subjects participated in two separate PET sessions. Maps reflecting low and high levels of painful tonic heat were obtained in the first session, and low and high levels of painful phasic heat in the second session. The subjects scored their peak pain intensity and unpleasantness on 10-cm visual analogue scales. For each subject, PET images were aligned to nuclear magnetic resonance (NMR) images and remapped into the standardized co-ordinate system of Talairach. After normalization of the PET volumes, subtraction images were formed voxel-by-voxel and converted to a t-statistic volume. The perceived pain intensity and unpleasantness were identical with painful tonic and phasic heat stimulation. Directed searches revealed significant blood-flow increases in the contralateral primary sensorimotor cortex (MI/SI), SII, insular cortex and cingulate cortex when the low tonic heat map was subtracted from the high. A similar, but not identical, pain-processing network was observed for the maps representing the subtraction of low and high phasic heat. In this subtraction, the blood-flow increases in MSI/SI did not reach statistical significance, and significant blood flow decreases were found in the contralateral middle temporal gyrus. Finally, the location of the activation site in the cingulate cortex was different from that observed during tonic heat pain. This study has provided more evidence for the existence of a common pain-processing network engaged during the perception of different levels of toxic and phasic heat pain. Copyright 1998 European Federation of Chapters of the International Association for the Study of Pain.

Pain perception and response: central nervous system mechanisms

Although several decades of studies have detailed peripheral and ascending nociceptive pathways to the thalamus and cerebral cortex, pain is a symptom that has remained difficult to characterize anatomically and physiologically. Positron emission tomography (PET) and functional magnetic imaging (fMRI) have recently demonstrated a number of cerebral and brain stem loci responding to cutaneous noxious stimuli. However, intersubject variability, both in the frequency and increased or decreased intensity of the responses, has caused uncertainty as to their significance. Nevertheless, the large number of available imaging studies have shown that many areas with recognized functions are frequently affected by painful stimuli. With this evidence and recent developments in tracing central nervous system connections between areas responding to noxious stimuli, it is possible to identify nociceptive pathways that are within, or contribute to, afferent spino-thalamo-cortical sensory and efferent skeletomotor and autonomic motor systems. In this study it is proposed that cortical and nuclear mechanisms for pain perception and response are hierarchically arranged with the prefrontal cortex at its highest level. Nevertheless, all components make particular contributions without which certain nociceptive failures can occur, as in pathological pain arising in some cases of nervous system injury.

Pain and functional imaging

Functional neuroimaging has fundamentally changed our knowledge about the cerebral representation of pain. For the first time it has been possible to delineate the functional anatomy of different aspects of pain in the medial and lateral pain systems in the brain. The rapid developments in imaging methods over the past years have led to a consensus in the description of the central pain responses between different studies and also to a definition of a central pain matrix with specialized subfunctions in man. In the near future we will see studies where a systems perspective allows for a better understanding of the regulatory mechanisms in the higher-order frontal and parietal cortices. Also, pending the development of experimental paradigms, the functional anatomy of the emotional aspects of pain will become better known.

Reduced immunoreactivity to calcium-binding proteins in Purkinje cells precedes onset of ataxia in spinocerebellar ataxia-1 transgenic mice

Earlier we have shown alterations in immunoreactivity (IR) to the calcium-binding proteins parvalbumin (PV) and calbindin D-28k (CaB) in surviving Purkinje cells of patients with spinocerebellar ataxia-1 (SCA-1). In the present study we determined PV and CaB expression (by immunohistochemical and immunoblot analyses) in Purkinje cells of transgenic mice (TM) expressing the human SCA-1 gene with an expanded (line B05) and normal (line A02) CAG tract, as well as in age-matched nontransgenic mice (nTM). Heterozygotes in the B05 line develop progressive ataxia beginning around 12 weeks of age. A02 animals are phenotypically indistinguishable from wild-type (nontransgenic) animals. In the cerebella of 8-, 9-, and 12-week-old TM-B05 there was a progressive decrease in PV IR in Purkinje cells compared with nTM and TM-A02. Parvalbumin immunostaining in interneurons was well preserved in all groups. A progressive decrease was also observed in CaB IR in Purkinje cells of 8-, 9-, and 12-week-old TM-B05. Cerebellar Purkinje cells of 6-week-old TM-B05, which exhibit no ataxia and even lack demonstrable Purkinje cell loss, also revealed reduction in PV IR. This change was matched by a significant decrease in the amount of cerebellar PV in 6-week-old TM-B05 as determined by Western blot analysis. Calbindin D-28K immunohistochemistry did not detect any marked changes in CaB IR within Purkinje cells at 4 weeks. However, at 6 weeks immunostaining and immunoblot analysis revealed a significant decrease in CaB in TM-B05 compared with controls. These data suggest that decreased levels of calcium-binding proteins in Purkinje cells in SCA-1 transgenic mice may cause alteration in Ca2+ homeostasis.

Brain glucose metabolism in borderline personality disorder

We searched for regional cerebral metabolic disturbances in patients with borderline personality disorder (BPD). Ten inpatients with BPD, no current DSM-IIIR Axis I diagnosis and free of any psychotropic substances, were compared with 15 age-matched control subjects using positron emission tomography with 2-deoxy-2-[18F]fluoro-D-glucose and semiquantitative analysis of regional glucose metabolic activity. We found relative hypometabolism in patients with borderline personality disorder at the level of the premotor and prefrontal cortical areas, the anterior part of the cingulate cortex and the thalamic, caudate and lenticular nuclei. This study shows significant cerebral metabolic disturbances in patients with borderline personality disorder. These metabolic disturbances, which are similar to some of those described in other psychiatric entities, may help to understand the characteristic clinical aspects of this disorder.

Decreased parvalbumin immunoreactivity in surviving Purkinje cells of patients with spinocerebellar ataxia-1

The distribution of two calcium-binding proteins, calbindin D28k (CaBP) and parvalbumin (PV), was investigated by immunohistochemistry in the brains of three individuals dying of nonneurologic illness and three patients with spinocerebellar ataxia-1 (SCA-1). SCA-1 has recently been proven to be due to an unstable CAG repeat mutation on chromosome 6. In the cerebellum of control individuals the Purkinje cells showed strong immunoreactivity to CaBP. Other cells were CaBP-negative. Parvalbumin was highly localized to Purkinje, basket, stellate, and Golgi cells. All surviving Purkinje cells in SCA-1 were strongly immunoreactive to CaBP. The number of PV-immunoreactive Purkinje cells was markedly reduced in SCA-1. In addition, there was a significant decrease in the intensity of PV immunostaining within the individual Purkinje cells compared with controls. However, in the hippocampus, temporal cortex, and lateral geniculate scattered PV-positive neurons were seen in SCA-1 patients, similar to those in controls. The present results suggest that the decreased PV-immunoreactivity in the surviving Purkinje cells in SCA-1 may reflect biochemical alterations preceding Purkinje cell degeneration.

Pain-related somatosensory evoked potentials in dementia

Pain-related somatosensory evoked potentials (pain SEPs) were examined in 25 demented and non-demented patients to investigate the cognitive function for pain in the progression of dementia. Pain SEPs by CO2 laser stimulation were recorded together with auditory event-related potentials (auditory ERPs). P340 in pain SEPs and P300 in auditory ERPs were analysed. The latency of P300 evoked in mildly demented patients was inversely correlated with the Mini-Mental state examination score, and the latency of P340 was also inversely correlated to that score but to a lesser extent. Pain SEPs were not recorded in 4 of 7 severely demented patients. These results indicate that the P340 component of pain SEPs is apparently different from the P300 component of auditory ERPs and suggest that the pain perception in severely demented patients may be abnormal.

Intraoperative EEG changes in relation to the surgical procedure during isoflurane-nitrous oxide anesthesia: hysterectomy versus mastectomy

STUDY OBJECTIVES

To investigate topographical changes in electroencephalographic (EEG) frequencies and spectral power density in relation to different surgical procedures (abdominal hysterectomy versus mastectomy) during steady-state isoflurane-nitrous oxide (N2O) anesthesia.

DESIGN

Prospective, nonrandomized, open study.

SETTING

University hospital.

PATIENTS

34 ASA status I and II patients scheduled for elective abdominal hysterectomy or mastectomy.

INTERVENTIONS

12 patients were studied without surgery (Group I, control). 22 patients were studied for the first 14 minutes following skin incision during hysterectomy (Group 2, n = 11) or mastectomy (Group 3, n = 11).

MEASUREMENTS AND MAIN RESULTS

Anesthesia was maintained with 0.6% isoflurane in 66% N2O in oxygen (O2). EEG was recorded via 17 channels followed by calculation of spectral power densities in selected frequency bands for each recording site. In addition, heart rate, mean arterial pressure (MAP), end-tidal carbon dioxide tensions, and isoflurane concentration were recorded. Total observation time was 20 minutes in all groups. At baseline, EEG variables were comparable in all groups. The EEG demonstrated slow wave activity superimposed with alpha waves. Start of surgery resulted in increases of slower waves and decreases in alpha activity. In both surgical groups, these EEG changes were most pronounced at frontal recording sites (p < 0.05) with differences in the frequency content. In Group 2 (hysterectomy), delta-activity became dominant, whereas in Group 3 (mastectomy), a shift to theta waves was observed. During surgery MAP was increased by 40% (Group 2; p < 0.05) and 21% (Group 3; p < 0.05), respectively.

CONCLUSIONS

These results show that specific surgical procedures may induce EEG slow wave activity to a different degree. The EEG response varied in relation to the surgical procedure and/or the intensity of noxious stimulation. Mastectomy resulted in the appearance of theta activity whereas, during laparotomy, the EEG frequency content was shifted to delta waves. The topographical analysis indicates spatial inhomogeneities in the EEG responses with a dominance at frontal areas. From this findings, it may be concluded that the electrode montage used for intraoperative EEG recordings has to be carefully selected.

Chronic pain is associated with deficits in information processing

Beginning with the theoretical premise that pain stimuli are liable to perturb the ordinary dynamical state of the brain, we hypothesized that individuals in pain may experience impaired information processing. A sample of 19 persons complaining of chronic pain and a comparison sample of 25 persons having sustained head trauma were obtained by retrospective chart review. The chronic-pain group consisted of 19 persons whose primary complaint was significant chronic pain, with no known history of head trauma or neurologic disorder. The comparison group consisted of 25 persons who had sustained mild to moderate head traumas. All subjects were administered information processing and motor subtests of the Human Performance Measurement System, a computerized set of measures. Both groups obtained mean z scores below the normative mean on all measures except visual digit span. There were no differences between groups on motor measures, visual digit span, and visual-spatial memory. On 2 of 6 information-processing tests, pain patients performed more poorly than head-trauma patients. The results suggest that pain may disrupt cognitive performances which depend on intact speed and capacity of information processing.

Cerebral responses to pain in patients with atypical facial pain measured by positron emission tomography

The localised PET cerebral correlates of the painful experience in the normal human brain have previously been demonstrated. This study examined whether these responses are different in patients with chronic atypical facial pain. The regional cerebral responses to non-painful and painful thermal stimuli in six female patients with atypical facial pain and six matched female controls were studied by taking serial measurements of regional blood flow by PET. Both groups displayed highly significant differences in responses to painful heat compared with non-painful heat in the thalamus, anterior cingulate cortex (area 24), lentiform nucleus, insula, and prefrontal cortex. These structures are closely related to the "medial pain system". The atypical facial pain group had increased blood flow in the anterior cingulate cortex and decreased blood flow in the prefrontal cortex. These findings show the importance of the anterior cingulate cortex and the reciprocal (possibly inhibitory) connections with the prefrontal cortex in the processing of pain in patients with this disorder. A hypothesis is proposed to explain the mechanisms of cognitive and pharmacological manipulation of these pain processes.

Encoding of the subjective intensity of sharp dental pain

This paper is a review and a discussion of our own pain research over the last decade. It is of a methodological and theoretical character and deals with preparation technique, choice of electrodes, control experiments involving pulpotomy and reliability tests of psychophysical methods for pain measurements, and the neuronal population encoding of sharp dental pain. The electrophysiological recording technique selectively picks up electrical activity induced in pulpal A-delta nerve fibers. The sensation of pain was quantified by means of an intermodal matching technique, finger span (PAS), in combination with sensory verbal descriptors covering a range from very, very weak to maximal pain. When a cold stimulus, ethyl chloride, was applied on the tooth surface a close agreement was demonstrated between intradental A-delta nerve activity (INA) and the sensation magnitude of pain (PAS) with respect to curve amplitude and time course. The high covariation of the neural and perceptual response measures indicated a good internal validity and confirmed also the basic soundness and the applicability of the procedures employed. For the purpose of further analyzing the functional relation of INA to PAS we studied specifically the effect of cold stimuli of different intensity on the integrated nerve response. Only sharp, shooting pain was accepted as a sensorial, perceptual correlate of the intradental A-delta nerve activity. Since an increase in amplitude was generally accompanied by an increase in duration of the responses, the fundamental question was raised how to best describe and characterize the neural and perceptual responses so that they most adequately reflect the information processing of the intensive aspect of sharp dental pain.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain dynamics and hypnosis: attentional and disattentional processes

This article reviews recent research findings, expanding an evolving neuropsychophysiological model of hypnosis (Crawford, 1989; Crawford & Gruzelier, 1992), that support the view that highly hypnotizable persons (highs) possess stronger attentional filtering abilities than do low hypnotizable persons, and that these differences are reflected in underlying brain dynamics. Behavioral, cognitive, and neurophysiological evidence is reviewed that suggests that highs can both better focus and sustain their attention as well as better ignore irrelevant stimuli in the environment. It is proposed that hypnosis is a state of enhanced attention that activates an interplay between cortical and subcortical brain dynamics during hypnotic phenomena, such as both attentional and disattentional processes, among others, are important in the experiencing of hypnosis and hypnotic phenomena. Findings from studies of electrocortical activity, event-related potentials, and regional cerebral blood flow during waking and hypnosis are presented to suggest that these attentional differences are reflected in underlying neurophysiological differences in the far fronto-limbic attentional system.

Brain-imaging studies of cognitive functions

Little is understood about the brain, the mind and their relationships. However, rapid technical advances in brain-imaging devices such as positron emission tomography (PET), functional magnetic resonance imaging, EEG and EMG have increased the capabilities for visualizing the working brain, and uncovering the cerebral areas participating in the realization of cognitive tasks, and progress in cognitive science has led to a better understanding of the functional architecture of mental abilities. There is, therefore, considerable potential for achieving a greater understanding of the relationships between cognition and cerebral structures through brain-imaging studies of mental functions. However, these studies are confronted with a series of difficulties related to the assumptions that govern their application, the constraints imposed by these techniques on the design of cognitive experiments, the complexities inherent in establishing relations between cognition and anatomy through physiology, and to the interpretation of patterns of cerebral activation. In this article, potential difficulties are described drawing essentially on examples from PET studies of cognitive functions. Whereas a bright future lies ahead for the study of human brain mapping, many problems still have to be overcome and solved in order to exploit the full potential of new brain-imaging techniques.

A cerebral blood flow study on tonic pain activation in man

This study examined brain areas involved in tonic pain perception. Cerebral blood flow was assessed by dynamic Xenon-133 inhalation single-photon emission tomography (SPET) in 7 healthy right-handed male volunteers undergoing the cold pressor test (CPT). In single experimental sessions, each subject was scanned twice, once in the resting state and once while immersing the left hand in freezing water (0 degrees C +/- 1). Immersion of the hand induced severe pain (visual analogue scale: 6.9 +/- 1.9) in all subjects. After correction for pCO2, cerebral blood flow was analyzed by placing a template of square regions of interest (ROIs) over 5 selected tomographic slices. Relative to the resting-state values, during the CPT, flow determinations revealed a 7-8% regional blood flow increase in the contralateral frontal lobe and bilateral temporal regions and a 15% flow increase in a ROI located over the primary sensorimotor cortex in the tomogram at 80 mm above the orbito-meatal line (corresponding to the cortical somatotopic representation of the hand) contralateral to the stimulated side. The tonic pain induced by the CPT thus appears to activate the contralateral frontal and bilateral temporal regions and more prominently, the primary sensorimotor cortex. This pattern of activation suggests that tonic painful stimuli activate the cortex partly via complex circuits and partly via direct somatosensory pathways.

Effects of hypnosis on regional cerebral blood flow during ischemic pain with and without suggested hypnotic analgesia

Using 133Xe regional cerebral blood flow (CBF) imaging, two male groups having high and low hypnotic susceptibility were compared in waking and after hypnotic induction, while at rest and while experiencing ischemic pain to both arms under two conditions: attend to pain and suggested analgesia. Differences between low and highly-hypnotizable persons were observed during all hypnosis conditions: only highly-hypnotizable persons showed a significant increase in overall CBF, suggesting that hypnosis requires cognitive effort. As anticipated, ischemic pain produced CBF increases in the somatosensory region. Of major theoretical interest is a highly-significant bilateral CBF activation of the orbito-frontal cortex in the highly-hypnotizable group only during hypnotic analgesia. During hypnotic analgesia, highly-hypnotizable persons showed CBF increase over the somatosensory cortex, while low-hypnotizable persons showed decreases. Research is supportive of a neuropsychophysiological model of hypnosis (Crawford, 1991; Crawford and Gruzelier, 1992) and suggests that hypnotic analgesia involves the supervisory, attentional control system of the far-frontal cortex in a topographically specific inhibitory feedback circuit that cooperates in the regulation of thalamocortical activities.