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M C Bushnell

Publications and source records attributed to M C Bushnell.

At least 37 records · Page 2Linked to original sources
PubMed1994

Distributed processing of pain and vibration by the human brain.

Pain is a diverse sensory and emotional experience that likely involves activation of numerous regions of the brain. Yet, many of these areas are also implicated in the processing of nonpainful somatosensory information. In order to better characterize the processing of pain within the human brain, activation produced by noxious stimuli was compared with that produced by robust innocuous stimuli. Painful heat (47-48 degrees C), nonpainful vibratory (110 Hz), and neutral control (34 degrees C) stimuli were applied to the left forearm of right-handed male subjects. Activation of regions within the diencephalon and telencephalon was evaluated by measuring regional cerebral blood flow using positron emission tomography (15O-water-bolus method). Painful stimulation produced contralateral activation in primary and secondary somatosensory cortices (SI and SII), anterior cingulate cortex, anterior insula, the supplemental motor area of the frontal cortex, and thalamus. Vibrotactile stimulation produced activation in contralateral SI, and bilaterally in SII and posterior insular cortices. A direct comparison of pain and vibrotactile stimulation revealed that both stimuli produced activation in similar regions of SI and SII, regions long thought to be involved in basic somatosensory processing. In contrast, painful stimuli were significantly more effective in activating the anterior insula, a region heavily linked with both somatosensory and limbic systems. Such connections may provide one route through which nociceptive input may be integrated with memory in order to allow a full appreciation of the meaning and dangers of painful stimuli. These data reveal that pain-related activation, although predominantly contralateral in distribution, is more widely dispersed across both cortical and thalamic regions than that produced during innocuous vibrotactile stimulation. This distributed cerebral activation reflects the complex nature of pain, involving discriminative, affective, autonomic, and motoric components. Furthermore, the high degree of interconnectivity among activated regions may account for the difficulty of eliminating pathological pain with discrete CNS lesions.

Adult↗
PubMed1993

Thalamic VPM nucleus in the behaving monkey. I. Multimodal and discriminative properties of thermosensitive neurons.

1. The role of the thalamic ventroposterior medial (VPM) nucleus in the discriminative aspects of nociception and thermoreception was evaluated in alert, trained rhesus monkeys. Single-unit responses were recorded from VPM while the monkeys performed a battery of tasks involving noxious heat, innocuous cool, and air-puff stimuli presented to the face. The discriminative ability of the monkey was compared directly with the responses of single neurons, to determine whether the neuronal response could subserve the monkey's discriminative behavior. 2. Most thermally sensitive neurons exhibited multimodal properties. Only 18% responded exclusively to heat (HT-Heat neurons), whereas 27% responded to innocuous mechanical, as well as noxious mechanical and heat stimuli (WDR-Heat). Twenty-three percent responded to innocuous mechanical stimuli and innocuous skin cooling (Mechano-Cool), and 32% responded to mechanical, innocuous cool, and noxious heat stimuli (WDR-Heat-Cool). 3. Almost all mechanical receptive fields were confined to one division of the trigeminal nerve. This was true for all of the above categories of VPM neurons, even those showing highly convergent properties (WDR-Heat-Cool). 4. Heat-activated neurons produced graded responses to noxious skin heating in the 46 to 49 degrees C range. Stimulus-response functions of neurons that responded to both heat and cool did not differ from those of neurons that responded exclusively to skin heating. 5. When the monkeys were detecting small changes in the intensity of a noxious heat stimulus (e.g., from 47 to 47.1-47.8 degrees C), heat-activated neurons responded to the smallest temperature changes that could be detected by the monkeys. Further, there was a high correlation between the monkey's success in detecting the stimulus changes and the magnitude of the neuronal responses to those changes. 6. Although the responsiveness of VPM cool-activated neurons was not compared with the monkeys' threshold for detecting cooling changes, larger stimulus changes (2 degrees C) that the monkey reliably detected produced significant neuronal responses. Further studies are needed to determine whether VPM neurons respond to the smallest detectable changes in skin cooling. 7. Several thermally sensitive VPM neurons were tested under two attentional conditions: 1) while the monkey was required to attend to a visual stimulus, and 2) while it was required to attend to the thermal stimulus to obtain reward. None showed a significant difference in heat- or cool-evoked activity in the two attentional states.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1993

Thalamic VPM nucleus in the behaving monkey. II. Response to air-puff stimulation during discrimination and attention tasks.

1. Single-unit activity was recorded in the ventral posterior medial (VPM) thalamic nucleus of awake monkeys while they performed detection and discrimination tasks involving tactile air-puff stimuli presented to the face. Neuronal responsiveness was compared directly with the monkey's discriminative performance. In addition, neuronal activity was compared when the monkey's attention was directed to the air-puff stimulus and when it was directed to a concurrent visual stimulus. 2. Neurons responding to the air-puff stimuli were classified as slowly adapting (SA), rapidly adapting (RA), inhibitory (IN), or multimodal (MM), according to their responses to manual and thermal stimulation, as well as their adaption rates to the air puff. Of 47 neurons responsive to air-puff stimulation and studied extensively in the behavioral task, 14 were classified as RA, 15 as SA, 6 as IN, and 12 as MM. The 12 MM neurons were so classified because, in addition to air puff, they responded to noxious heat, innocuous cooling, or noxious pinch. 3. Neurons from each class had restricted contralateral receptive fields localized within one division of the trigeminal nerve. There was no systematic difference in receptive-field size among groups. 4. A prominent difference in tactile responsiveness of MM neurons was response latency. Although the mean latency for RA, SA, and IN neurons was not significantly different (6.1, 9.1, and 12.2 ms, respectively), the mean latency for MM neurons was significantly longer than that for each of the other neuronal categories (28.8 ms; Ps < 0.001). These data suggest that the excitatory tactile afferent input to MM neurons is different from that to low-threshold neurons. 5. For RA, SA, and MM neurons the frequency of the neuronal discharge evoked by the air-puff stimulation was proportional to the intensity of the air puff. Thus responses of each neuronal class coded air-puff stimulus intensity. 6. The monkeys' ability to detect air-puff stimuli of various intensities was compared with the frequency of neuronal responses to those stimuli. Both the percent success in detecting differences in air-puff intensity and the detection latency were highly correlated with neuronal response frequency. The responses of all three excitatory neuronal categories corresponded well with the monkey's performance. Thus any or all of RA, SA, and MM neurons could play a role in the discrimination of air-puff intensities.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1993

Thalamic VPM nucleus in the behaving monkey. III. Effects of reversible inactivation by lidocaine on thermal and mechanical discrimination.

1. The present study evaluates the necessity of the ventroposterior medial thalamic nucleus (VPM) for discrimination of the intensity of noxious heating, innocuous cooling, and innocuous tactile (airpuff) stimulation of the maxillary skin. 2. Two rhesus monkeys were trained to detect small differences (< 1.0 degrees C) in the intensity of noxious heat (near 46 degrees C) and innocuous cold (near 30 degrees C) as well as differences in the force of an airpuff applied to the skin over the maxilla. As a control the monkeys also detected small differences in the intensity of a white light. Lidocaine hydrochloride (2%) was microinjected into regions of thalamus where single-unit recordings had identified neuronal responses to the noxious heating and/or cooling stimuli. The effectiveness of the anesthetic blockade was monitored by multiunit recordings using microelectrodes positioned 1-3 mm from the orifice of the injection cannula. The monkey's ability to detect near-threshold changes in stimulus intensity was compared before and after each injection. 3. During six experimental sessions, single injections of 1-4 microliters lidocaine near the dorsomedial border of VPM did not significantly alter the monkey's ability to detect small changes in the intensity of noxious heat, cool, airpuff, or visual stimuli despite neurophysiological evidence that spontaneous neuronal activity was blocked within parts of VPM. 4. During three experiments, dual simultaneous microinjections of lidocaine (delivered through 2 microcannulae separated by approximately 1 mm) resulted in profound deficits in noxious heat discrimination, with lesser deficits in cool and airpuff discrimination; visual discrimination was never altered. Monitoring of adjacent microelectrodes revealed that although activity ventral to the injection sites was blocked, activity in medial thalamic nuclei, implicated in nociceptive processing, was probably not altered by these injections. 5. These data suggest that VPM is important for the perception of noxious and innocuous thermal stimuli as well as for the perception of tactile stimuli. However, considering the ineffectiveness of small single microinjections of lidocaine, it appears that some critical proportion of VPM must be inactivated to disrupt thermal or tactile discrimination, possibly because of overlapping receptive field properties of neurons in different areas of the nucleus.

Animals↗
PubMed1992

A psychophysical comparison of sensory and affective responses to four modalities of experimental pain.

It is generally accepted that the sensory and affective components of pain may be differentially associated with various acute and chronic diseases, and that some treatment regimens are best directed toward certain aspects of the pain experience. In addition, experimental animal models have been described that presume to assess either the sensory-discriminative aspects of phasic pain or the affective responses associated with tonic pain. The present psychophysical experiment directly compares the perceived intensity and unpleasantness of sensations evoked by four types of experimental noxious stimuli: contact heat, electric shock, ischemic exercise, and cold-pressor pain. A novel pain measurement technique is described that incorporates unbounded magnitude-estimation/category scales; this technique allows precise ratio responses, while minimizing within- and between-subject variability. We observe that, relative to the perceived intensity of the individual stimuli, subjects consistently differentiate among the degrees of unpleasantness evoked by the four stimulus modalities. Ischemic exercise and cold-pressor pain evoke higher estimates of unpleasantness, and thus may better mimic the pain of chronic disease. The relative unpleasantness produced by contact heat is significantly less than that of the other modalities tested, and therefore contact heat stimuli may be ideally suited for assessing sensory-discriminative aspects of pain perception. Possible neurophysiological mechanisms underlying the observed differences in perceived unpleasantness are discussed in relation to the growing body of literature concerning tonic and phasic pain stimuli.

Adult↗
PubMed1991

Multiple representations of pain in human cerebral cortex.

The representation of pain in the cerebral cortex is less well understood than that of any other sensory system. However, with the use of magnetic resonance imaging and positron emission tomography in humans, it has now been demonstrated that painful heat causes significant activation of the contralateral anterior cingulate, secondary somatosensory, and primary somatosensory cortices. This contrasts with the predominant activation of primary somatosensory cortex caused by vibrotactile stimuli in similar experiments. Furthermore, the unilateral cingulate activation indicates that this forebrain area, thought to regulate emotions, contains an unexpectedly specific representation of pain.

Adult↗
PubMed1991

The effects of dorsal column stimulation on measures of clinical and experimental pain in man.

Despite the extensive use of dorsal column stimulation (DCS) for the control of various chronic pain conditions, most clinicians report only modest success rates. Surprisingly, there has been little placebo-controlled investigation of its efficacy for altering either clinical or experimental pain perception. The current study compared the effects of DCS to placebo stimulation on clinical pain perception, perceived intensity of painful heat stimuli and visual stimuli, and the discrimination of small changes in noxious heat intensity and in light intensity. We found that DCS, but not placebo stimulation, significantly altered ratings of spontaneous clinical pain as well as those of painful cutaneous heat. In addition, heat discrimination thresholds were increased by DCS, but not placebo. On the other hand, DCS had no effect on ratings of visual stimulus intensity nor on visual discrimination, suggesting that the DCS modulation of pain perception was not due to a general change in attention. These data indicate that DCS significantly alters pain transmission in humans. Nevertheless, the relatively small reduction in clinical pain (less than 30%) must be weighed against the invasive nature of electrode implantation.

Adult↗
PubMed1991

Modulation of heat pain perception by high frequency transcutaneous electrical nerve stimulation (TENS).

Although many studies have indicated that high frequency nonpainful transcutaneous electrical nerve stimulation (TENS) reduces clinical pain, controlled studies of the modulation of experimental pain by TENS have produced conflicting results. This study evaluated the effect of high frequency nonpainful TENS on heat pain perception using a model that we have previously shown to be sensitive to other nonpharmacological analgesic treatments. We found that TENS significantly reduced subjects' ratings of painful and near painful heat stimuli (43-51 degrees C) (p = 0.01) and increased the pain threshold from 46.7 to 47.9 degrees C (p = 0.002). Placebo stimulation had no effect on the subjects' ratings or on their pain thresholds. Furthermore, TENS did not alter subjects' ratings of visual stimuli, indicating that the analgesic effect was not due to a nonspecific distraction. These data suggest that TENS alters the perception of experimentally produced natural pain stimuli. The TENS related modulation also appears to be comparable to that produced by other nonpharmacological analgesic manipulations such as counterirritation and changes in attention.

Adult↗
PubMed1991

Electrical stimulation of peripheral and central pathways for the relief of musculoskeletal pain.

One method for the treatment of chronic musculoskeletal pain involves stimulation of the peripheral or central nervous system. Such stimulation includes transcutaneous electrical nerve stimulation, dorsal column stimulation, and deep brain stimulation. This review discusses the clinical use of electrical stimulation for the relief of musculoskeletal pain, and describes the results of studies conducted in our laboratory suggesting that such stimulation reduces pain transmission along sensory-discriminative pathways.

Animals↗
PubMed1990

The perception of painful and nonpainful stimuli during voluntary motor activity in man.

Previous studies have shown that voluntary movement diminishes the transmission of cutaneous afferent input through the dorsal column-medial lemniscal system, and also raises the threshold for detecting nonpainful, cutaneous stimuli (electrical shocks). Although there is some evidence that pain elicited by electrical stimulation is diminished during movement, no studies have tested the effect of movement on the perception of pain produced by natural stimulation. For this reason, we tested the effects of voluntary motor activity on the perception of noxious thermal stimuli in human volunteers. We first developed a motor paradigm in which the thermal stimulation could be applied to the immobile limb (isometric elbow flexion-extension). Both isometric and isotonic muscle contractions about the elbow increased the threshold for detecting weak cutaneous stimuli (electrical shocks) applied to the forearm, and to a lesser extent the detection of stimuli applied to the dorsum of the hand. Afterwards, noxious and innocuous heat stimuli were applied to the forearm during isometric contractions and at rest. Magnitude estimates for the intensity of the pain, as well as latency measures of the onset of pain, were recorded. We found no evidence that isometric motor activity diminished either the threshold for pain or the subjective intensity of the noxious and innocuous thermal stimuli. Thus, motor activity decreases the ability to detect weak low-threshold cutaneous inputs, but has no effect on the perception of warmth and heat pain.

Arousal↗
PubMed1989

A primate model for the study of tonic pain, pain tolerance and diffuse noxious inhibitory controls.

A primate model of cold pressor pain is described in which the animal itself initiates all trials, may terminate painful stimuli at any time, and controls the duration of the experimental session, thus avoiding the inadvertent administration of intolerable pain stimuli. Pain tolerance time varies directly with stimulus intensity and is sensitive to motivational factors. This model will facilitate the study of endogenous pain-modulatory pathways and the assessment of analgesic treatments in animals.

Adaptation, Physiological↗
PubMed1989

Sensory and affective aspects of pain perception: is medial thalamus restricted to emotional issues?

Lateral and medial thalamus are traditionally thought to have separate roles in pain processing, with lateral lemniscal regions transmitting discriminative information about location and intensity, while medial nonspecific regions are involved in emotional responses. Contrary to this view, the present study shows that some single neurons in medial thalamus of alert monkey discriminate changes in the intensity of noxious stimuli that are equal to or below the monkey's own discrimination threshold. Since these neurons are also modulated by anesthesia and attentional factors, we suggest that parts of medial thalamus may participate in both discriminative and affective dimensions of pain.

Action Potentials↗
PubMed1989

Responses of monkey medullary dorsal horn neurons during the detection of noxious heat stimuli.

1. We examined the activity of thermally sensitive trigeminothalamic neurons and nonprojection neurons in the medullary dorsal horn (trigeminal nucleus caudalis) in three monkeys performing thermal and visual detection tasks. 2. An examination of neuronal stimulus-response functions, obtained during thermal-detection tasks in which noxious heat stimuli were applied to the face, indicated that wide-dynamic-range neurons (WDR, responsive to innocuous mechanical stimuli with greater responses to noxious mechanical stimuli) could be subclassified based on the slope values of linear regression lines. WDR1 neurons exhibited significantly greater sensitivity to noxious heat stimulation than WDR2 neurons or nociceptive-specific neurons (NS, responsive only to noxious stimuli). 3. In one behavioral task, the monkeys detected 1.0 degrees C increases in noxious heat from preceding noxious heat stimuli ranging from 44 to 48 degrees C. WDR1, WDR2, and NS neurons increased their discharge frequency as a function of the intensity of the first noxious heat temperature (T1) as well as the final temperature (T2). The responses of WDR1 neurons were greater than those produced by WDR2 or NS neurons across all the temperatures examined. The order of stimulus presentation affected the responses of WDR1 neurons to 1.0 degrees C increases in the noxious heat range but not those of WDR2 or NS neurons. 4. In a second behavioral task, the monkeys detected small increases in noxious heat (0.2-0.8 degrees C) from a first temperature of 46 degrees C. Although the responses of all three classes of neurons were monotonically related to stimulus intensity, WDR1 neurons exhibited greater sensitivity to small temperature increases than either WDR2 or NS neurons. 5. Subpopulations of all three classes of neurons exhibited responses that were independent of thermal stimulus parameters or sensory modality and that only occurred during the behavioral task. These task-related responses were time-locked to specific behavioral events associated with trial initiation and trial continuation. 6. These data provide evidence that a subpopulation of WDR neurons is the dorsal horn cell type most sensitive to small increases in noxious heat in the 45-49 degrees C temperature range and provides the most information about stimulus intensity. The findings support the view that nociceptive neurons have the capacity to precisely encode stimulus features in the noxious range and that WDR neurons are likely to participate in the monkeys' ability to perceive the intensity of such stimuli.

Afferent Pathways↗
PubMed1989

The correlation of monkey medullary dorsal horn neuronal activity and the perceived intensity of noxious heat stimuli.

1. We examined the relationship between the activity of medullary dorsal horn nociceptive neurons and the monkeys' ability to detect noxious heat stimuli. In two different detection tasks, the temperature of a contact thermode positioned on the monkey's face increased from 38 degrees C to temperatures between 44 and 48 degrees C (T1). After a variable time period, the thermode temperature increased an additional 0.2-1.5 degrees C (T2), and the monkeys' detection speed from the onset of T2 was determined. We previously have established that detection speed is a measure of the perceived intensity of noxious thermal stimuli. Nociceptive neurons were classified as wide-dynamic-range (WDR, responsive to innocuous mechanical stimuli with greater responses to noxious mechanical stimuli) and nociceptive-specific (NS, responsive only to noxious stimuli). WDR neurons were subclassified as WDR1 and WDR2 based on the higher slope values of the stimulus-response functions of WDR1 neurons. The monkeys were trained to detect small increases in noxious heat, and their detection speeds were correlated with the responses of WDR1, WDR2, and NS neurons. 2. Detection speeds to T2 temperatures of 1.0 degrees C from preceding T1 temperatures of 45 and 46 degrees C were faster during a preceding ascending series of stimuli than during a descending series. Similarly, the peak discharge frequencies of WDR1 neurons in response to the same stimuli were greater during the ascending series of T2 temperatures. In contrast, the responses of WDR2 and NS neurons showed no significant differences during the ascending and descending series of stimuli. 3. Detection speeds following 0.4, 0.6, and 0.8 degrees C T2 stimuli were higher when the preceding T1 temperature was 46 degrees C as compared with detection speeds to the identical stimuli when the preceding T1 temperature was 45 degrees C. WDR1 neurons also exhibited a significant increase in peak discharge frequency to these same T2 stimuli when the preceding T1 temperature was 46 degrees C. In contrast, the neuronal activity of WDR2 and NS neurons did not differ on 45 and 46 degrees C T1 trials. 4. The relationship between detection speed and neuronal peak discharge frequency was examined in response to different pairs of T1 and T2 stimuli when T1 was either 45 or 46 degrees C. There was a significant correlation between detection speed and neuronal discharge for WDR1 and WDR2 neurons. No correlation was observed for NS neurons. 5. The magnitude of neuronal activity on correctly detected and nondetected trials was compared when T1 was 46 degrees C and T2 was 0.2 degree C.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Preoperative flurbiprofen in oral surgery: a method of choice in controlling postoperative pain.

The analgesic efficacy of a single 50-mg preoperative dose of flurbiprofen was compared with ACC-30 (aspirin 375 mg, codeine 30 mg, caffeine 30 mg) and a placebo. Forty patients scheduled for the surgical removal of impacted maxillary third molars were enrolled in a double-blind, randomized study. Using a within-subject design we compared the analgesic efficacy of (1) preoperative flurbiprofen 50 mg with placebo in 20 patients, and (2) preoperative ACC-30 with placebo in 20 other patients. Using a between-group design, we then compared the analgesic efficacy of (3) each drug given preoperatively and postoperatively, and (4) each drug given postoperatively only. Patients rated 2 pain dimensions, intensity and unpleasantness, hourly for 8 hours after the presurgical dose. The results of this study indicate that better analgesia was obtained when flurbiprofen was given preoperatively compared to only after surgery. Conversely, preoperative administration of ACC-30 did not demonstrate any significant influence on postsurgical analgesia. When comparing the 2 drugs, flurbiprofen proved to be superior in providing pain relief only when it was given prior to surgery. There was no difference between them when given only after surgery. Side effects were moderate and not significantly different between patients receiving flurbiprofen and those receiving ACC-30.

Adult↗
PubMed1987

Mechanical response properties of ventroposterior medial thalamic neurons in the alert monkey.

The properties of trigeminal cutaneous thalamic neurons were explored in alert cynomolgous monkeys to determine receptive field and response characteristics. Two monkeys received juice reward for sitting quietly while an investigator probed the monkey's face with mechanical stimuli. Extracellular single unit recordings were made from the ventroposterior medial thalamic nucleus (VPM), and mechanical response properties were evaluated for each cell having an extraoral cutaneous receptive field. Of 89 cells examined, 90% responded best to innocuous tactile stimulation, and were classified as low threshold. The other 10%, classified as wide dynamic range, showed a graded response to increasingly intense stimuli, with a maximum discharge to noxious pinch. Of the low threshold neurons, most exhibited excitatory responses, with about half being rapidly adapting and the others slowly adapting. The spontaneous activity of 11% of the low threshold neurons was inhibited by stimulation of the neuron's receptive field. There was no systematic difference in receptive field size for the various types of neurons, but the receptive fields of wide dynamic range cells were smaller than those previously observed in trigeminopthalamic neurons of the medullary dorsal horn. The wide dynamic range and inhibitory low threshold neurons were located primarily in the caudal third of VPM, while the excitatory low threshold neurons were located throughout. In summary, response characteristics of VPM neurons show more diversity in the alert monkey than has been reported in paralyzed and/or anesthetized animals.

Adaptation, Physiological↗
PubMed1987

Sensory perception during movement in man.

The ability of subjects to perceive innocuous stimuli in the presence and absence of movement was evaluated using electrical stimulation of the skin. The subjective intensity of suprathreshold stimuli was unchanged during movement. Discrimination of small differences in the intensity of suprathreshold stimuli (difference thresholds) was also not altered by movement while, in the same subjects, detection thresholds were increased during movement of the stimulated arm. These results suggest that the elevation of detection thresholds during movement can be explained by masking. Both active and passive movement of the stimulated limb increased detection thresholds, with active movement having a slightly greater and more consistent effect than passive movement. Thus, both central and peripheral feedback factors appear to play a role in diminishing one's ability to detect weak stimuli during movement. Attention was also shown to influence performance of the detection task.

Electric Stimulation↗