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Biomedical subjects

C E Chapman

Publications and source records attributed to C E Chapman.

At least 37 records · Page 2Linked to original sources
PubMed1996

Cortical mechanisms underlying tactile discrimination in the monkey. I. Role of primary somatosensory cortex in passive texture discrimination.

1. The discharge patterns of 359 single neurons in the hand representation of primary somatosensory cortex (SI) of two monkeys (Macaca mulatta) were recorded during the performance of a passive texture discrimination task with the contralateral hand (104 in area 3b, 149 in area 1, and 106 in area 2). Three nyloprint surfaces were mounted on a drum that was rotated under the digit tips. One surface was entirely smooth, whereas the other two were smooth over the first half and rough over the second half (smooth/ rough) (raised dots, 1 mm high and 1 mm diam, in a rectangular array; spatial period of 3 mm across the rows and columns for most recordings; 9 mm between columns for selected recordings). The monkeys were trained to distinguish between the smooth and smooth/rough surfaces. After the surface presentation, the monkey indicated the texture of the second half of the surface by pushing or pulling, respectively, on a lever with the other arm. For most recordings an average tangential speed of 49 mm/s was tested. For selected recordings motor speed was incremented (63, 75, or 89 mm/s). 2. Two hundred eighty-three neurons had a cutaneous receptive field (RF) on the hand (96 in area 3b, 120 in area 1, and 67 in area 2). Thirty-five neurons had a deep RF (4 in area 3b, 15 in area 1, and 16 in area 2). Seven neurons had mixed cutaneous and deep RFs (4 in area 1, 3 in area 2). Thirty-four neurons had no identifiable RF (4 in area 3b, 10 in area 1, and 20 in area 2). 3. The discharge of 185 of 359 neurons was significantly modulated during the presentation of one or both surfaces compared with the discharge at rest. Cells with a cutaneous RF that included part or all of the distal phalangeal pads of the digits used in the task (usually digits III and IV) were more likely to be modulated during surface presentation (132 of 179, 74%) than those with a cutaneous RF not in contact with the surfaces (24 of 104, 23%). The remaining neurons (mixed, deep, or no RF) were also infrequently modulated (29 of 76, 38%). 4. Of the 185 modulated units, 118 cells were classified as texture related because there was a significant difference in the discharge rate evoked by the smooth/rough and smooth surfaces. Cells with a cutaneous RF that included the digital pads in contact with the surfaces were frequently texture related (100 of 132, 76%). Texture sensitivity was less frequently observed in the remaining modulated neurons (18 of 53, 34%: cutaneous RF not in contact with the surfaces, deep RF, mixed cutaneous and deep RF, no identifiable RF). 5. Texture-related neurons were found in areas 3b, 1, and 2. Two patterns of texture-related responses were observed in the 100 cutaneous units with an RF in contact with the surfaces. Thirty-one units were classified as showing a phasic response at the time the digits encountered the leading edge of the rough half of the surface. Fifty-eight cells were classified as phasic-tonic (or sometimes tonic at the slowest motor speeds) because the response lasted for the duration of the presentation of the rough portion of the surface. The remaining 11 neurons could not be readily classified into one or the other category and, indeed, generally showed clear texture-related responses only at higher motor speeds (> 49 mm/s, 9 of 11). 6. Speed sensitivity was systematically evaluated in 41 of 100 texture-related units with a cutaneous RF in contact with the surfaces. The discharge of 66% of the units (27 of 41) varied significantly with the speed of surface presentation, with discharge increasing at higher speeds. Speed sensitivity was found in all three cytoarchitectonic areas (6 of 6 cells in area 3b, 11 of 22 in area 1, and 10 of 13 in area 2). 7. Contact force was also systematically monitored in these experiments (69 of 100 texture-related cells with a cutaneous RF in contact with the surfaces). Linear regression analyses indicated than 22% (15 of 69) of the texture-related units were sensitive to contact force (13

Animals↗
PubMed1995

Effects of cross-modal manipulations of attention on the ability of human subjects to discriminate changes in texture.

Cross-modal manipulations of attention significantly affect the detectability of tactile stimuli, but the effects on a more complex perceptual task, the discrimination of surface texture, are unknown. This study sought to examine whether attention influences the ability to discriminate a change in texture during passive touch. Twelve subjects were trained to perform two discrimination tasks: discriminating an increase in the intensity of a visual stimulus, and discriminating a change in the texture of a surface that was displaced beneath the tip of one digit. The texture change consisted of an increase in the spatial period between rectangular arrays of raised dots on Nyloprint surfaces, and for each subject an increment close to his or her discrimination threshold was employed in the experiment. Each trial began with the presentation of two baseline stimuli: A standard voltage illuminated the visual stimulus (an array of yellow light-emitting diodes (LEDs), and a standard texture (3-mm spatial period) was displaced under the tip of digit 3. For visual trials, three different increments in luminous intensity were presented, at one of three different delays following the initial presentation of the baseline stimuli. For texture trials, a single increment in spatial period was presented at one of three delays after the onset of the baseline stimuli. In any one trial, only one modality changed in intensity. The subject's task was to signal, as quickly as possible, the occurrence of the change. Instructional cues (red and green LEDs) were used to direct the subjects' attention toward the modality that changed (valid cue), to divide the subjects' attention between the visual and tactile modalities (neutral cue) as either might change, or to direct the subjects' attention toward the modality that did not change (invalid cue). Two measures of performance were employed: accuracy (percentage correct) and reaction time (speed with which the subject responded). The results indicated that cue condition significantly influenced the ability of subjects to discriminate a change in texture: Both accuracy and speed were significantly improved when subjects' attention was selectively directed toward the textured surface, as compared to when it was misdirected toward the visual modality. Performance was intermediate when attention was divided between the two modalities. The results were compared with those obtained previously in a tactile detection task using a similar attentional manipulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Perception of vibrotactile stimuli during motor activity in human subjects.

Previous studies have shown that voluntary motor activity decreases the ability to detect near-threshold electrical stimuli applied to the skin, but has no effect on the perception of either suprathreshold electrical stimuli or natural thermal stimuli (warmth, heat pain). The present study was undertaken to determine if the perception of natural tactile stimuli (vibrotactile) is diminished by motor activity (rhythmical isometric flexions and extensions about the elbow). The stimuli were applied at three different sites on the operant arm--ventral forearm, thenar eminence and distal digit--to examine also the influence of the proximity of the stimulated site to the active muscles on perception. The ability to detect near-threshold stimuli at the two more proximal stimulation sites was significantly reduced during the motor task, and these effects were more pronounced and widespread with higher levels of target force (20 N vs 50 N). Discrimination of small differences in the intensity of suprathreshold stimuli, at all three sites, was unchanged during the motor task. Finally, the subjective intensity of suprathreshold vibrotactile stimuli was reduced, in a nonlinear fashion, during the motor task; proximity again influenced the degree of modulation. In contrast a previous study showed no change in magnitude estimates of suprathreshold electrical stimuli during isotonic flexion and extension. Some possible reasons for the discrepancy are discussed. In addition, our previous suggestion that movement produces a simple reduction in the signal-to-noise ratio (i.e. the gating signal modelled as a masking stimulus) cannot explain the present results, so more complex models are required.

Adult↗
PubMed1994

Active versus passive touch: factors influencing the transmission of somatosensory signals to primary somatosensory cortex.

Active and passive touch, respectively with and without voluntary movement on the part of the subject, are frequently reported to be equivalent in terms of the resultant perceptual abilities. This review reexamines the notion of perceptual equivalence in the light of growing evidence that the transmission of tactile inputs is diminished, or "gated," during the course of active movement. It is concluded that there is indeed gating of cutaneous inputs during active touch. In most experiments, the paradoxical observation of perceptual equivalence between active and passive touch can partly be explained by the choice of task, namely, tactile discriminations that depend on relative, and not absolute, differences in inputs. The surprising lack of evidence for any superiority of passive touch over active touch can likely be explained by several factors. First, performance with active touch may be enhanced by the motor strategy, e.g., by reducing the speed of movement at critical points, and so reducing the degree of gating, and (or) by optimally orienting the exploring digits so as to bring the most sensitive skin areas into contact with the object in question. Second, central influences, including attention and motor set, may be specifically activated during voluntary movement and contribute to enhancing performance during active touch. Thus, the gating influences associated with active touch may be offset, partly or wholly, by the combined influence of these factors to yield (near) perceptual equivalence for active and passive touch.

Animals↗
PubMed1992

Regional transfusion centre preoperative autologous blood donation programme: the first two years.

OBJECTIVE: To assess the efficacy of a regional autologous blood donation programme. DESIGN: Clinical and laboratory data were collected and stored prospectively. Transfusion data were collected retrospectively from hospital blood bank records. SETTING: Northern Region Blood Transfusion Service and 14 hospitals within the Northern Regional Health Authority. SUBJECTS: 505 patients referred for autologous blood donation before elective surgery. MAIN OUTCOME MEASURES: Patient eligibility, adverse events from donation, autologous blood units provided, and autologous and allogeneic blood units transfused within 10 days of operation. RESULTS: Of 505 patients referred, 354 donated at least one unit. 78 of 151 referred patients who did not donate were excluded at the autologous clinic, mostly because of anaemia or ischaemic heart disease. In 73 cases the patient, general practitioner, or hospital consultant decided against donation. 363 autologous procedures were undertaken. In 213 (59%) cases all requested units were provided. The most common reasons for incomplete provision were late referral or anaemia. Adverse events accompanied 24 of 928 donations (2.6%). Transfusion data were obtained for 357 of the 363 procedures. 281 donors were transfused; autologous blood only was given to 225, autologous and allogeneic blood was given to 52, and allogeneic blood only was given to four. 648 of 902 (72%) units of autologous blood were transfused. Complete provision of requested autologous units was followed by allogeneic transfusion in 12 of 208 procedures (5.8%). Incomplete provision was followed by allogeneic transfusion in 44 of 149 procedures (30%). CONCLUSIONS: This study shows the feasibility of a regional autologous transfusion programme. Autologous donors only infrequently received allogeneic transfusion. Patients should be appropriately selected and referred early.

Blood Banks↗
PubMed1992

Discharge properties of neurones in the hand area of primary somatosensory cortex in monkeys in relation to the performance of an active tactile discrimination task. II. Area 2 as compared to areas 3b and 1.

The discharge patterns of 144 single cortical neurones, within the cutaneous representation of the hand in area 2 (primary somatosensory cortex, SI), were studied in two rhesus monkeys during the performance of an active tactile discrimination task. These were compared to those previously described for units within areas 3b and 1 recorded from the same animals. The task consisted of making a single scanning movement of the digit tips over a surface (first half smooth; second half either smooth or rough). The nature of the texture encountered over the second half of the surface was indicated by the monkey making a differential lever response (push or pull) with the opposite hand. During the task, area 2 units with cutaneous receptive fields (RFs) on the digit tips of interest (those scanned over the surfaces) generally showed an increase in their discharge (75%); patterns of decreased discharge or no modulation (respectively, 12 and 13%) were rarely observed. Units with digital cutaneous RFs not in contact with the stimuli were much more likely to show either a pattern of decreased discharge or no modulation whatsoever (47% in each case), suggesting that there is some selection of cutaneous inputs in this task in that non-active inputs are selectively gated. For units with a cutaneous RF, the sign of modulation changed significantly across SI, in a manner consistent with a pattern of increased convergence onto the more caudal regions of SI. Overall, the proportions of area 2 units with digital RFs on the tips of interest that were classified as either texture-related (25%) or movement-related (26%) were similar to those reported previously for areas 3b and 1, suggesting that their presumed roles in, respectively, the analysis of surface texture and the representation of the physical parameters of movement are shared and distributed across the three cytoarchitectonic subdivisions of SI under consideration. In addition, the discharge patterns of single texture-related cells in areas 3b, 1 and 2 did not reliably signal whether or not the animal successfully discriminated the surfaces, suggesting that information from a population of cells is required for the performance of the task. Texture-related responses in area 2 were, however, unique in two ways. Firstly, 35% of the texture-related units had additional discharges related to the performance of the scanning movement (texture- and movement-related cells); no such units were found in area 3b, and only one was encountered in area 1.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Modulation of the cutaneous responsiveness of neurones in the primary somatosensory cortex during conditioned arm movements in the monkey.

The present experiments were designed to investigate the neuronal mechanisms, at the level of the primary somatosensory cortex, which underlie the observation that somatosensory cortical potentials evoked by air puff stimuli directed at the forearm are decreased, in a nonspecific and widespread manner, during voluntary movements about the elbow. Unitary discharge was recorded from 131 cells receiving cutaneous input from the hairy skin of the forearm or hand (areas 3b and 1) of two monkeys trained to perform rapid movements of the contralateral arm (elbow flexion or extension). Evoked unitary responses to air puff stimuli applied to the centre of the cell's receptive field, at various delays before and after the onset of movement, were recorded. Movement produced a significant decrease in the short latency excitatory response to the air puff in 89% of the cells (117/131); the remaining 11% were not modulated by movement. This movement-related "gating" of cutaneous inputs occurred regardless of the response pattern of the cells to movement alone, being observed in 91% of the cells with no movement-related discharge, and 89% of those with movement-related discharge. The air puff responses of cells with inputs from the forearm and the dorsum of the hand were all similarly modulated by movement and the modulation was clearly present prior to the onset of movement (mean onset, -66 ms). Variation in the depth of modulation as a function of the direction of the movement, flexion or extension, was observed in only a very small proportion of the modulated units (16/117); most showed no relationship to direction. It is suggested that, in this experimental situation, much of the modulation appears to occur at a pre-cortical level since there was no relationship between the pattern of discharge of cells in relation to movement alone and the pattern of movement-related gating of their responses to the air puff. Effects which might be consistent with a cortical origin for the modulation were only infrequently observed. The present results are strikingly similar to those obtained using the evoked potential method, and thus support the hypothesis that in this task of rapid elbow movements, movement modulates the transmission of cutaneous signals from the hairy skin of the distal forelimb to primary somatosensory cortex in a nonspecific and widespread fashion.

Animals↗
PubMed1991

Discharge properties of neurones in the hand area of primary somatosensory cortex in monkeys in relation to the performance of an active tactile discrimination task. I. Areas 3b and 1.

The present experiments were designed to characterize the discharge patterns of single cortical neurons within the cutaneous representation of the hand in postcentral cortex (areas 3b and 1) in awake monkeys during the performance of an active tactile discrimination task. The task consisted of making a single scanning movement over a surface (first half smooth; second half smooth or rough); the texture encountered over the second half of the surface was indicated by the animal, respectively, pushing or pulling a lever. Unitary discharge was recorded from 118 cells receiving input from the hand or distal forearm of two monkeys. Units with cutaneous fields on the digit tips in contact with the surfaces to be discriminated showed an increase in discharge (58%), a decrease in discharge (11%) or no change (31%) during the task. Units with cutaneous fields not in contact with the discriminanda were much more likely to show decreased discharge during the task (25%), suggesting that there is some selection of cutaneous inputs in this task. Cutaneous units in areas 3b and 1 were equally likely to signal differences in texture (respectively, 18% and 26% of those with digital receptive fields (RFs] and most of the texture-related units (78%) had a large RF, spanning several digits. The discharge patterns of single texture-related cells did not reliably signal whether or not the animal successfully discriminated the surfaces: unitary responses were occasionally absent even though the animal correctly identified the surface or they were present when an incorrect response was made. This observation suggested that information derived from a population of cells is required for the performance of the task, since no single cell's discharge contained sufficient information upon which the animal could base its behavioural response. A group of cells with digital RFs (24% of area 3b cells and 15% of area 1 units) were classified as movement-related. Their discharge signalled precisely the onset and/or end of movement, and they were generally insensitive to the texture of the surfaces scanned. Such cells may serve as an independent source of information for primary somatosensory cortex related to the physical parameters of movement. Most cells with digital RFs were more responsive during active tactile discrimination than during passive movement of the digits over the surfaces (monkey no longer required to discriminate the surface texture). For area 3b units, peripheral factors (RF orientation, speed of movement) were likely responsible for this observation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Can the use of physical modalities for pain control be rationalized by the research evidence?

Physical modalities, including cold and heat, are widely used in the conservative management of pain associated with musculoskeletal disorders. This review has critically appraised the literature supporting the use of these modalities in the treatment of musculoskeletal pain. It was concluded that, apart from a few exceptions and in a few types of disorders, existing evidence does not support the use of these modalities in long-term pain control. There was, however, evidence that several modalities, specifically cold and a form of deep heat (shortwave diathermy), do have short-lived analgesic effects and so may contribute to more painfree function in the short term. Further research is clearly warranted to define the short- and long-term therapeutic efficacy of physical modalities in the treatment of musculoskeletal pain to justify their continued use in clinical practice.

Animals↗
PubMed1991

The effects of cross-modal manipulations of attention on the detection of vibrotactile stimuli in humans.

Although it is well known that attention to a visual or auditory stimulus can enhance its perception, less is known concerning the effects of attention on the perception of natural tactile stimuli. The present study was conducted to examine the magnitude of the effect of cross-modal manipulations of attention in human subjects on the detection of weak, low-frequency vibrotactile stimuli delivered to the glabrous skin of the finger pad of the right index finger via an Optacon. Three suprathreshold vibrotactile arrays (40 Hz), varying in the number of activated pegs and hence the area of skin stimulated, were used. Subjects were trained to detect the occurrence of vibrotactile or visual stimuli and to respond by pressing a foot pedal as quickly as possible thereafter. Two instructional lights were used to cue the subjects as to which stimulus modality they should attend, in three experimental conditions. In the first cue condition, the forthcoming stimulus modality was indicated by the illumination of its associated light. In the second cue condition, both instructional lights were illuminated, and the subjects were asked to divide their attention equally between the two modalities. In the third cue condition, the stimulus modality was falsely indicated by the illumination of the cue not associated with the stimulus to be presented. Reaction times (RTs) were calculated for each trial. For each modality, tactile and visual, the RTs varied significantly with the cue condition, with the mean RT changing in a graded manner across the experimental conditions (being shortest for the correctly cued condition, intermediate for the neutrally cued condition, and longest for the incorrectly cued condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Changes in hip position modulate soleus H-reflex excitability in man.

The effects of hip flexion and extension on the ipsilateral soleus Hoffmann (H) reflex recruitment curve were studied in 11 healthy subjects. Hip flexion (50 degrees), but not hip extension (15-20 degrees), produced changes in the H-reflex. A maintained facilitation, peaking at intensities of stimulation producing a maximal H-reflex (Hmax), was observed in 6/18 sessions. Inhibition, peaking at intensities submaximal for Hmax, was seen in 7/18 sessions. In some of the latter experiments, there was also a facilitation at high intensities of stimulation (greater than Hmax). The remaining experiments were classified as showing no effect: 3 were unmodulated but 2 showed a facilitation at high intensities of stimulation (greater than Hmax). Since the knee was extended in the test position, a second series of experiments (n = 7) were carried out to determine the possible influence of stretch of the biarticular hamstrings muscle group on the soleus H-reflex by comparing the effects of hip flexion with the knee extended with those obtained when the knee was flexed, thereby relaxing the hamstrings. The results provided no evidence that the variability could be explained by differences in the relative degree of stretch on the hamstrings muscle group. There were, however, systematic variations in the shape of the corresponding control H-reflex recruitment curves between subjects: the mean slope of the rising limb of the recruitment curve was highest in those experiments showing an inhibition, intermediate in the ineffective experiments and lowest in those showing a maintained facilitation. These observations indicate that the reflex output studied was different in the three groups, possibly reflecting differences in the relative proportions of slow- and fast-twitch motor units contributing to the reflex response.

Achilles Tendon↗
PubMed1990

Modulation of cutaneous cortical evoked potentials during isometric and isotonic contractions in the monkey.

The effects of the direction of movement (flexion vs extension) and the nature of the motor task (isotonic vs isometric) on the modulation of sensory cortical evoked responses to cutaneous stimulation were investigated in one monkey. Sensory responses were assessed by measuring the magnitude of the short latency component of air puff-evoked potentials recorded intracortically in the arm representation of areas 3b and 1 in the primary somatosensory cortex. At most recording sites, it was found that the amplitude of the air puff-evoked potential was decreased in a non-specific manner by motor activity. Neither the timing nor the depth of the modulation were found to vary with either the direction or the type of contraction. The effects were widespread since inputs from practically the entire forelimb (hairy skin) were diminished during the motor tasks. These results thus show that the modulation was more closely linked to the central motor output than to the peripheral input generated by muscle force and/or limb displacement. It is suggested that signals originating from central motor structures, acting in a feedforward manner, play a major role in 'gating' cutaneous inputs during movement. It is further suggested that the centrally mediated effects are exerted via a final common pathway upon which the 'gating' signals converge.

Animals↗
PubMed1990

Modulation of somatosensory evoked responses in the primary somatosensory cortex produced by intracortical microstimulation of the motor cortex in the monkey.

Previous studies have shown that the amplitude of somatosensory evoked potentials is diminished prior to, and during, voluntary limb movement. The present study investigated the role of the motor cortex in mediating this movement-related modulation in three chronically prepared, awake monkeys by applying low intensity intracortical microstimulation (ICMS) to different sites within the area 4 representation of the arm. Air puff stimuli were applied to the contralateral arm or adjacent trunk at various delays following the ICMS. Somatosensory evoked potentials were recorded from the primary somatosensory cortex, areas 1 and 3b, with an intracortical microelectrode. The principal finding of this study was that very weak ICMS, itself producing at most a slight, localized, muscle twitch, produced a profound decrease in the magnitude of the short latency component of the somatosensory evoked potentials in the awake money. Higher intensities of ICMS (suprathreshold for eliciting electromyographic (EMG) activity in the "target" muscle, i.e. that muscle activated by area 4 stimulation) were more likely to decrease the evoked response and produced an even greater decrease. The modulation appeared to be, in part, central in origin since (i) it preceded the onset of EMG activity in 23% of experiments, (ii) direct stimulation of the muscle activated by ICMS, which mimicked the feedback associated with the small ICMS-induced twitch, was often ineffective and (iii) the modulation was observed in the absence of EMG activity. Peripheral feedback, however, may also make a contribution. The results also indicate that the efferent signals from the motor cortex can diminish responses in the somatosensory cortex evoked by cutaneous stimuli, in a manner related to the somatotopic order. The effects are organized so that the modulation is directed towards those neurones serving skin areas overlying, or distal to, the motor output.

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

Renal failure in myelomatosis.

Renal failure is a common presenting feature in myelomatosis. This review offers a practical means for classifying renal failure in this disease. Three groups are identified: (1) those patients whose renal failure improves or is stable when they are maintained on a high fluid intake; (2) the minority of patients whose renal failure progresses despite high fluid intake; and (3) those patients who are fluid-intolerant due to oliguric renal failure or congestive cardiac failure. The difference between groups 1 and 2 is not simply due to differences in response to chemotherapy, for many group-1 patients achieve improvement in renal function without or before loss of light chain proteinuria. It is concluded that all patients with myelomatosis with excess monoclonal free light chain proteinuria are at risk from developing renal failure of the type associated with group 1. The chances of them doing so are diminished if they maintain a high fluid intake. Group 2 encompasses a range of conditions not all of which are clearly defined. There is generally a poor correlation between the physical characteristics of light chains and the presence of group-2 renal failure.

Acute Kidney Injury↗
PubMed1988

Modulation of lemniscal input during conditioned arm movements in the monkey.

Modulation of sensory transmission in the lemniscal system was investigated in 2 monkeys trained to perform a simple elbow flexion in response to an auditory cue. Evoked responses to peripheral stimulation were recorded in the medial lemniscus, sensory thalamus (ventral posterior lateral nucleus, caudal division, VPLc) and somatosensory cortex. Simultaneous recordings were made from the cortex and either the medial lemniscus or VPLc. At all recording sites, evoked responses to natural (air puff) or electrical, percutaneous stimulation were depressed prior to and during active movement. The time course of the depression was similar at all three levels; the magnitude of the decrease during movement was most pronounced at the cortical level. Cortical evoked responses to central stimulation of effective sites in either the medial lemniscus or VPLc were decreased during, but not before, the onset of movement. The decrease was less than that seen for peripheral evoked potentials. Passive movement of the forearm significantly decreased all but the lemniscal evoked potential. The results indicate that there is a centrally mediated suppression of somatosensory transmission prior to, and during movement, occurring at the level of the first relay, the dorsal column nuclei. During movement, reafferent signals from the moving arm decrease transmission at the thalamocortical level.

Animals↗
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↗