Cerebral Potentials Research Articles

Neurophysiological Tools for Small Fiber Assessment in Painful Diabetic Neuropathy (Comment Letter)

We would like to congratulate Veves et al. for their excellent review that stressed the importance of painful diabetic neuropathy diagnosis [1]. However, apart from neuropathic pain scales and skin biopsy, we believe that neurophysiological tools are also useful in the diagnostic work-up of diabetic patients with neuropathic pain complaints due to small fiber involvement. Small fiber function can be noninvasively assessed by quantitative sensory testing for thermal sensation [2], in which warm and heat pain thresholds reflect the function of C- and Ad-fibers, respectively. This method has been proposed in the assessment of patients with diabetic neuropathy [3], but is limited by the subjectiveness of the individual’s responses [4]. In the last few years, more objective techniques have been developed for small fiber assessment. Lasergenerated radiant heat pulses selectively activate Ad and C nociceptors [5] and have been used for the early diagnosis of diabetic neuropathy [6,7]. Unfortunately, because of the imminent risk for skin lesions—especially in diabetic subjects—its use is not recommended in routinary basis. More recently, contact heat-evoked potentials have been introduced for small fiber evaluation without the risk of cutaneous lesions [8]. The system delivers rapidly raising heat stimuli through a thermode placed in the skin, able to evoke cerebral potentials reliably [9,10], and has been used for the study of many small fiber syndromes [9–11] with a good correlation with the density of C fibers in the superficial skin [10].

The effect of temporal accuracy constraints on movement-related potentials

Both self-paced movements (internally generated) and movements paced by a fixed interval cue (externally cued) are preceded by a slow-rising movement-related potential (MRP) of similar timing, magnitude and topography. When the timing of the external cue is variable (temporally unpredictable), this MRP is absent. These findings have been interpreted to suggest that MRPs reflect neural activity mediating the preparation of temporally predictive movements, irrespective of whether the movement is internally generated or externally cued. However, the apparent similarity between MRPs preceding self-paced and predictably cued movements might be explained by the absence of control for the timing of movement onset, that is, MRPs preceding regularly-paced cues may simply reflect activity associated with self-paced movements initiated at times that more or less coincide with the timing of the imperative cue. The objective of this study was to reexamine the comparison of MRPs preceding temporally predictive (self-paced and predictably cued) versus reactive movements. To circumvent the potential confound of movement onset timing, constraints were placed on the temporal accuracy of movements cued by a regularly-paced tone. This design permitted post-hoc classification of trials into predictive or reactive movements to the tone. Three movement initiation conditions were tested: (1) self-paced (SP), (2) in response to an irregularly-paced cue (IC), and (3) in response to a regularly-paced cue (RC). In the latter condition, subjects were trained to initiate movement to within less than one simple reaction time in at least 50% of trials, and MRPs were compared between movements that were initiated "too early" (predictive), "too late" (reactive), or were temporally accurate (predictive). Cerebral potentials were recorded from 87 scalp surface electrodes. Consistent with previous studies, an early slow-rising MRP with maximum negativity over the midline frontal cortex was present only when the timing of movement onset could be predicted in advance (SP and RC conditions). Moreover, MRPs for movements that were temporally accurate or were initiated "too early" were significantly larger than the MRPs that preceded SP movements (P < 0.018). In contrast, movements initiated in reaction to the cue (IC condition), even when the timing of the cue could be predicted in advance (movement initiated "too late" in the RC condition), were associated with a significant attenuation of premovement activity (P < 0.005). Differences between conditions (RC > SP > IC) were significantly greater over the midline frontal cortex than the contralateral or ipsilateral sensorimotor cortex (P < 0.038). These findings show that the imposition of accuracy constraints on the timing of movement onset markedly enhances preparatory activity in the cortical or subcortical networks that mediate the predictive initiation of movement.

Electrical brain events associated with awareness of errors

Objective: The neurophysiological correlates of mental activity and awareness are important to define, as they permit the objective study of these psychological phenomena. Methods: In a choice reaction task, subjects were asked to respond to tone pips by extending their fingers and to make non-semantic vocalizations as soon as they became aware of any errors. Results: In motor response-synchronized averages of instances in which subjects were aware of making errors, a biphasic cerebral potential occurred over the frontocentral scalp region 170 ms after the incorrect motor response and about 500 ms prior to any vocalization. It occurred 100 ms after the so-called error negativity (Ne), from which it was therefore distinguished. Conclusion: The recording of such activity may therefore provide an electrophysiological signature of perceptual awareness related to making errors. Significance: Recording this potential may facilitate the objective study of awareness to errors in other experimental contexts.

Neurophysiologische zerebrale Diagnostik in der Intensivmedizin

Die Diagnostik der Funktion des zentralen Nervensystems mit neurophysiologischen Verfahren besitzt in der neurologischen Intensivmedizin einen festen Platz. Neben der Elektroenzephalographie (EEG) hat sich die Untersuchung evozierter zerebraler Potenziale (EP) für die Untersuchung zentralnervöser Strukturen etabliert. Beide Methoden können sowohl diskontinuierlich zur Diagnostik und Prognosestellung als auch kontinuierlich zum Monitoring von schweren zentralnervösen Erkrankungen eingesetzt werden. Die verschiedenen Methoden erfassen jeweils bestimmte Einzelfunktionen des Gehirns und ergänzen sich daher in ihren diagnostischen und prognostischen Aussagen. Der sinnvolle Einsatz dieser Möglichkeiten erfordert eine genaue Kenntnis der klinischen Befunde und des Therapieverlaufs der Patienten. Der gezielte Einsatz von neurophysiologischen Methoden ist wertvoller als die unkritische Anwendung vieler Untersuchungsverfahren, die lediglich die Flut der medizinischen Daten fördert aber nicht zu einer besseren Einschätzung der klinischen Situation führen.

Establishment of a method of contact heat evoked potential and its application in carpal tunnel syndrome

To establish a method to evoke cerebral potentials by stimulating nociceptive fibers, estimate the conduction velocities of nerve fibers mediating these responses, and assess the value of the potentials in carpal tunnel syndrome. One hundred patients with carpal tunnel syndrome and 20 sex-, and aged-matched healthy persons underwent stimulation of contact heat delivered via a circular thermode to excite selectively nociceptors with a rapid rising time at 70 degrees C/s to elicit pain and contact heat evoked potential (CHEP). Thermal stimuli were sent at two intensity levels (49.5 degrees C and 54.5 degrees C) to three body sites: thenar eminence, dorsum of hand, and proximal volar forearm The CHEPs were recorded from Cz and Pz. The relation between the stimulus intensity and pain rating was observed, and the main components of the evoked potential were recorded. The nerve conduction velocity was calculated from the latency difference of the CHEP and center to center distance of distal and proximal stimulus arrays. The pain intensity ratings were 3.2 +/- 0.3 and 4.4 +/- 0.5 when the thenar eminence was stimulated at the temperature of 49.5 degrees C and 54.5 degrees C respectively; and the ratings were 6.3 +/- 0.8 and 7.2 +/- 0.5 on the dorsum of hand and proximal volar forearm at the temperature of 54.5 degrees C respectively. Three components, Cz/N550, Cz/P750, and Pz/P1000, were found in the evoked potentials. The latency of the CHEP was significantly correlated with the arm length, and not significantly correlated with sex, age, and side difference of the arm. The conduction velocities of the Adelta and C fibers of the carpal tunnel syndrome patients were 12.0 m/s +/- 5.6 m/s and 0.6 m/s +/- 0.1 m/s respectively, both lowered, being 93.8% and 99.5% of those of the healthy persons (12.9 m/s +/- 7.5 m/s and 1.7 m/s +/- 0.4m/s respectively). Elicited reliably, CHEP is mediated by Adelta and C fibers. The conduction velocity of C fibers in the patients with carpal tunnel syndrome is decreased.

Alterations in cerebral potentials evoked by rectal distention and drinking ice water in patients with irritable bowel syndrome

Visceral hypersensitivity has been found to be present in irritable bowel syndrome (IBS). The current study sought to study visceral afferent hypersensitivity in IBS patients and obtain further objective evidence of alterations in intestinal afferent pathways in IBS patients by cerebral evoked potentials (CEP). We studied 30 female IBS patients and 12 female healthy subjects. Rectal perception thresholds to balloon distention were measured and CEP was recorded in response to rhythmic rectal distention (two distention series, each of 100 repetitions at a frequency of 1 Hz) at the volume of perception thresholds. All subjects were then asked to drink 220 mL 4 degrees C ice water and the above steps were repeated 20 min later. Rectal distention led to recognizable and reproducible CEP. Compared to healthy subjects, IBS patients demonstrated significantly shorter N1, P1 and N2 latencies (P < 0.05). After drinking ice water, IBS patients exhibited further shortened N1, P1 and N2 latencies (P < 0.05), but drinking did not alter the latencies of healthy controls and the amplitudes of both IBS patients and healthy controls. The shorter latency of cerebral potentials evoked by rectal distention and ice water stimulation in IBS patients provided further objective evidence for defective visceral afferent transmission in IBS patients.

Emotionality and the temporospatial organization of instantaneous EEG potentials

The characteristics of the temporospatial organization of cerebral cortical potentials at different levels of genetically determined emotionality were analyzed by constructing topograms of instantaneous EEG levels in the inbred rat strains MR and MNRA. Two parameters were calculated for each topogram: the total level and the similarity coefficient. Power spectra were calculated for the values and these were found to change in an oscillatory manner. Interstrain differences were found in the correlated changes in total levels and similarity coefficients, in the durations of changes in the total level, which were more marked than those of similarity coefficients, and the nature of interhemisphere asymmetry. In MR rats, the power spectra of both measures showed significant peaks with modes at 2.0, 6.5, and 9.0 Hz. In MNRA rats, peaks in the spectra of these measures both coincided (2.0 Hz) and differed (7.0 Hz in the spectrum of the total level and 3.0, 4.5, and 6.0 Hz in the spectrum of the similarity coefficient). These data suggest different types of functioning of the reticulothalamocortical and hippocampocortical systems in rats of these strains.

Nonlinear correlation between evoked local cerebral blood flow and field potential in rat somatosensory cortex as a function of stimulus current

Nonlinear correlation between evoked local cerebral blood flow and field potential in rat somatosensory cortex as a function of stimulus current

Cortical myoclonus due to hypocalcemia 12 years after thyroidectomy

Although seizures have been described in hypocalcemia, myoclonus has been rarely reported. We report the first case of a patient with hypocalcemic cortical myoclonus due to hypoparathyroidism following a previous thyroidectomy. The patient was an 84-year-old woman who presented with multifocal myoclonus, which was predominant in the upper extremities, neck, jaw, and facial muscles. Electrophysiological studies revealed enlarged somatosensory evoked potentials, cortical reflexes evoked by peripheral nerve stimulation, and a cerebral potential preceding myoclonic jerks determined by jerk-locked averaging. All these findings were consistent with cortical myoclonus. The myoclonic state disappeared as serum calcium level became normal. Hypocalcemia should be considered in patients who had had a thyroidectomy, even if it was performed more than 10 years previously.

A Semiconductor Photostimulator for Electroencephalography with USB Bus Control

The paper contains a description of electroencephalography (EEG) photostimulator for examining the induced cerebral potentials. The device was designed to function within the EEG computer complexes; a high-intensity irradiation LED matrix is used as the light source. The 1.1 USB control bus serves as the communication interface; there is an extra external synchronization bus. It is possible to preset the frequency, brightness, on-off time ratio and pattern of light stimuli. A library of application programmer is supplied to monitor the photostimulation.

Stimulus recognition and its relationship to the cerebral event-related potential.

The relationship between the event-related cerebral potential (ERP) and perceptual awareness by the subject is poorly understood. The authors manipulated the process of stimulus recognition to examine the effect of changes in a subject's awareness on different components of the ERP and on behavioral (motor) responses. Ten subjects listened to a series of 400 tone pips, one of which (frequent tone) was slightly louder than the other (rare tone; 14% of trials). Stimuli were presented in blocks of 10 tones and, following each block, subjects were asked how many rare tones they had detected and if they were aware of any errors that they had made during that block. Cerebral and motor responses were recorded by surface electrodes. When subjects were aware of having responded erroneously to either the rare or frequent tone, their response times were shorter than for correct responses to that tone. When subjects were unaware of such errors, however, the response times were delayed compared to correct responses and to error responses of which the subject was aware. When the subject made an error by responding to the rare tone as if it were frequent and was aware of the error, the N2 and P3 latencies were delayed. By contrast, when subjects were unaware of such errors, no N2 or P3 components were present. Similar findings were noted when subjects responded to a frequent tone as if it were rare. These results suggest that the N2 and P3 components of the ERP reflect the awareness of the subject that an unexpected event has occurred, regardless of whether it is an unexpected stimulus or an unexpectedly erroneous response to that stimulus. The recording of ERP may provide a means of measuring perceptual awareness in other contexts.

Microneurographic study of C fiber discharges induced by CO 2 laser stimulation in humans

We investigated C-fiber discharges and cerebral potentials evoked by weak CO 2 laser beams applied to a tiny skin area in five healthy subjects. Microneurography was performed from the peroneal nerve in the right popliteal area. Cerebral potentials were recorded from the Cz electrode referred to linked earlobes. The mean conduction velocity of five stable single units was 1.1±0.3 m/s. The mean latency of the positive peak of cerebral potentials was 1327.4±46.2 ms. These findings indicated that this new stimulation method selectively activated C-fiber nociceptors of the skin.

Microneurographic study of C fiber discharges induced by CO2 laser stimulation in humans

We investigated C-fiber discharges and cerebral potentials evoked by weak CO 2 laser beams applied to a tiny skin area in five healthy subjects. Microneurography was performed from the peroneal nerve in the right popliteal area. Cerebral potentials were recorded from the Cz electrode referred to linked earlobes. The mean conduction velocity of five stable single units was 1.1±0.3 m/s. The mean latency of the positive peak of cerebral potentials was 1327.4±46.2 ms. These findings indicated that this new stimulation method selectively activated C-fiber nociceptors of the skin.

A inferência do shiatsu na distribuição de potência das ondas alfas no córtex cerebral em mulheres adultas

The inference of shiatsu on distribution of potency of alpha waves on cerebral cortex in adult women The humor level, the emotions and the level of muscular tension are directly related to cerebral waves activities. The electroencephalogram (E.E.G) is a non-invasive method and of highly sensibility for superficial registry of cerebral potential. The shiatsu it’s an oriental technique of massage that promotes relaxation and the subjective sensation of wellness. We believe the presence of alpha waves are related with specific mental state, characterizing tranquility and major tolerance to pain. Facing this, the objective of study it’s analyze the effects of induced relaxation through shiatsu, evaluating the physiologic response, verifying the behavior of the alpha waves through the EEG technique. The samples were selected among individuals of female sex with ages up to 35 yr. For the EEG application was utilized the BRAINTECH 3000 system (EMSA, medical instruments, Brazil). For the statistic procedure was utilized the T test matched for each pair of electrodes on alpha band. Was considered for significance level of p < 0.005. Were found significant differences on potentials of alpha band on electrodes T3 – F7 and T4 – F8.

The inference of shiatsu on distribution of potency of alpha waves on cerebral cortex in adult women

The humor level, the emotions and the level of muscular tension are directly related to cerebral waves activities. The electroencephalogram (E.E.G) is a non-invasive method and of highly sensibility for superfi cial registry of cerebral potential. The shiatsu it's an oriental technique of massage that promotes relaxation and the subjective sensation of wellness. We believe the presence of alpha waves are related with specifi c mental state, characterizing tranquility and major tolerance to pain. Facing this, the objective of study it's analyze the effects of induced relaxation through shiatsu, evaluating the physiologic response, verifying the behavior of the alpha waves through the EEG technique. The samples were selected among individuals of female sex with ages up to 35 yr. For the EEG application was utilized the BRAINTECH 3000 system (EMSA, medical instruments, Brazil). For the statistic procedure was utilized the T test matched for each pair of electrodes on alpha band. Was considered for signifi cance level of p < 0.005. Were found signifi cant differences on potentials of alpha band on electrodes T3 - F7 and T4 - F8.

Evidence of a specific spinal pathway for the sense of warmth in humans.

While research on human sensory processing shows that warm input is conveyed from the periphery by specific, unmyelinated primary sensory neurons, its pathways in the central nervous system (CNS) remain unclear. To gain physiological information on the spinal pathways that convey warmth or nociceptive sensations, in 15 healthy subjects, we studied the cerebral evoked responses and reaction times in response to laser stimuli selectively exciting Adelta nociceptors or C warmth receptors at different levels along the spine. To minimize the conduction distance along the primary sensory neuron, we directed CO(2)-laser pulses to the skin overlying the vertebral spinous processes. Using brain source analysis of the evoked responses with high-resolution electroencephalography and a realistic model of the head based on individual magnetic resonance imaging scans, we also studied the cortical areas involved in the cerebral processing of warm and nociceptive inputs. The activation of C warmth receptors evoked cerebral potentials with a main positive component peaking at 470-540 ms, i.e., a latency clearly longer than that of the corresponding wave yielded by Adelta nociceptive input (290-320 ms). Spinal neurons activated by the warm input had a slower conduction velocity (2.5 m/s) than the nociceptive spinal neurons (11.9 m/s). Brain source analysis of the cerebral responses evoked by the Adelta input yielded a very strong fit for one single generator in the mid portion of the cingulate gyrus; the warmth-related responses were best explained by three generators, one within the cingulate and two in the right and left opercular-insular cortices. Our results support the existence of slow-conducting second-order neurons specific for the sense of warmth.

Vorteile einer Nervenchirurgie mit intraoperativer Elektrodiagnostik

To date in most cases of high-grade nerve injuries only partial recovery is achieved and the prognosis is still poor for some types of lesions. Neurophysiological methods are implemented improve the outcome by assessing the condition of nerve fibres at any location and at any point of time during the course of surgery. Monitoring is utilised prevent inadvertent injury during surgical procedures. Free-running EMG signals are recorded from muscles targeted by a nerve at risk. Motor unit activity is initiated when dissecting instruments approach and contact the nerve. Bursts and neurotonic discharges arise and increase with tension or pressure exerted on the nerve. Acoustic feedback warns of imminent damage. Evoked muscle and cerebral potentials are applied reveal impairment of the nerve excitability and conductivity by mechanical and metabolic stress. Under normal conditions nerve action potential (NAP) recording from the exposed nerve reflects the integrity of the nerve by high amplitude, steep rise and normal temporal dispersion. Under pathological conditions the reduced density of nerve fibres, thickening of nerve sheaths, endoneurial cell proliferation and many other influences enhance the amplitude reduction of the NAP and may cause overestimation of nerve malfunction. However, this enhancement facilitates the detection of the location and the extension of the lesion. In nerve tumour surgery NAP recording identifies affected and unaffected nerve fascicles and the border of healthy In traumatology following closed nerve injuries early revision and evaluation with the aid of NAP recording has proved be the best possible procedure. When the nerve is found in continuity, the appearance of the nerve does not reliably reflect the grade of the lesion and the prognosis. Resection of low-grade injuries, capable of spontaneous regeneration downgrades the outcome. If a high-grade lesion without potential of regeneration is not resected and repaired, recovery is not possible. To avoid inadequate measures, nerve surgery is frequently delayed awaiting muscle reinnervation. However, this loss of time has the most adverse impact on final outcome when repair is necessary. Neurography detects the presence or absence of significant nerve regeneration in the early months following the injury. Where the lesion is found in continuity after 3-4 months and NAPs are recorded across the lesion, neurolysis is done in order promote nerve regeneration. Where NAPs are not recordable, resection and repair are required. In the same way NAP recording is used judge single fascicles. Split nerve repair is done if some fascicles are conductive and others are not. When nerve repair is indicated, the proximal stump has be sectioned back to healthy tissue. However, as intraoperative nerve evaluation by gross inspection and magnification does not reliably reflect the availability and viability of nerve fibres, NAP recording is recommended as an additional criterion for choosing an appropriate proximal coaptation site for reconstruction. Intraoperative nerve function assessment is essential for brachial plexus surgery. As nerve repair is useless in the presence of preganglionic lesion, SEPs are applied assess the integrity of the dorsal root. NAPs with high amplitude in the absence of nerve function are also useful tools identify preganglionic lesions.

Alterations in cerebral potentials evoked by rectal distension in irritable bowel syndrome.

Central nervous system correlates of the visceral hyperalgesia documented in patients with irritable bowel syndrome are limited. Reproducible cerebral evoked potentials can be recorded in response to rhythmic balloon distension of the rectum in healthy adults. Irritable bowel syndrome patients and healthy subjects were studied to compare the characteristics of mechanically-evoked rectal cerebral potentials obtained during fasting and after the ingestion of a standard meal. Twenty-two pairs of age-matched healthy female subjects and female irritable bowel syndrome patients were studied. Cerebral evoked potentials were recorded in response to rhythmic rectal distension (two distension series each of 100 repetitions at 0.8 hertz); cerebral evoked potential recordings were repeated after a 1000 kcal (46% fat) liquid meal. Trait and state anxiety questionnaires were also completed. Compared to healthy subjects, irritable bowel syndrome patients demonstrated higher prevalence of cerebral evoked potential early peaks (latency < 100 ms) postprandially, and uniformly shorter cerebral evoked potential latencies both before and after feeding. These findings provide further objective evidence for defective visceral afferent transmission in irritable bowel syndrome patients.

Alterations in cerebral potentials evoked by rectal distension in irritable bowel syndrome

OBJECTIVE: Central nervous system correlates of the visceral hyperalgesia documented in patients with irritable bowel syndrome are limited. Reproducible cerebral evoked potentials can be recorded in response to rhythmic balloon distension of the rectum in healthy adults. Irritable bowel syndrome patients and healthy subjects were studied to compare the characteristics of mechanically-evoked rectal cerebral potentials obtained during fasting and after the ingestion of a standard meal. METHODS: Twenty-two pairs of age-matched healthy female subjects and female irritable bowel syndrome patients were studied. Cerebral evoked potentials were recorded in response to rhythmic rectal distension (two distension series each of 100 repetitions at 0.8 hertz); cerebral evoked potential recordings were repeated after a 1000 kcal (46% fat) liquid meal. Trait and state anxiety questionnaires were also completed. RESULTS: Compared to healthy subjects, irritable bowel syndrome patients demonstrated higher prevalence of cerebral evoked potential early peaks (latency < 100 ms) postprandially, and uniformly shorter cerebral evoked potential latencies both before and after feeding. CONCLUSION: These findings provide further objective evidence for defective visceral afferent transmission in irritable bowel syndrome patients.

Do cerebral potentials to magnetic stimulation of paraspinal muscles reflect changes in palpable muscle spasm, low back pain, and activity scores?

Objective: Previous studies have shown that cortical-evoked potentials on magnetic stimulation of muscles are influenced by muscle contraction, vibration, and muscle spasm. This study was carried out to determine whether these potentials correlate with palpatory muscle spasm, patient symptoms, and disability in patients with low back pain. Methods: A prospective observational study was performed on 13 subjects with a history of low back pain visiting an orthopedic hospital-based clinic. Patients were screened for serious pathologic conditions by an orthopedic surgeon. The patients were then evaluated for the presence of muscle spasm by one of the investigators who was blinded to the results of the evoked potential studies. Patients were asked to complete a low back pain visual analogue scale (VAS) and a Roland-Morris Activity Scale (RMAS). Cortical-evoked potentials were recorded with a magnetic stimulator placed over the lumbar paraspinal muscles with the patient in the prone position. The palpatory examination, VAS, RMAS, and the cortical potentials were repeated after 2 weeks of therapy commonly used to reduce muscle spasm. Results: The patients demonstrated a significant decrease in low back pain VAS and RMAS scores after treatment compared with before treatment. There was a reduction in the amount of palpatory muscle spasm in 11 of 13 cases. The cortical potentials before treatment were attenuated compared with previously reported controls and showed a significant increase before and after treatment in the amplitude of these potentials with multivariate analysis of variance. There was significant correlation between the changes in cortical potentials after treatment and the changes noted in paraspinal muscle spasm and VAS and RMAS scores. Conclusions: This study confirms the previous report that the amplitude of cerebral-evoked potentials on magnetic stimulation of paraspinal muscles is depressed in the presence of palpable muscle spasm. The close correlation among these potentials, paraspinal muscle spasm, and clinical symptoms suggests that the measurement of muscle activity may be more important in the assessment of low back pain than is commonly accepted. (J Manipulative Physiol Ther 2000;23:458-64)