Cerebral Potentials Research Articles

Zum Problem primär erloschener evozierter zerebraler Potentiale in der Hirntoddiagnostik

In a collective of 82 patients with the clinical signs of brain death and examination of evoked cerebral potentials the incidence of primary abolished evoked potentials was studied. The initial examination occurred at the same time after onset of disease in both groups. We found a marked correlation with the clinical course of the patients. Whereas the group with primary loss of evoked potentials mainly contained patients with intracerebral and subarachnoid hemorrhages and short survival times, the other group with primary preserved evoked potentials showed a high rate of ischemic infarctions and longer survival periods. The rate of primary abolished evoked potentials can be lowered only by routine examination at the earliest time possible. Outside of neurological intensive care units the early examination of evoked potentials is hardly possible. In these units, the EEG remains the technical examination of choice in the confirmation of brain death.

Magnetic stimulation of muscle evokes cerebral potentials

Somatosensory evoked potentials (SEPs) were recorded from the scalp in man to magnetic stimulation of various skeletal muscles. The potentials consisted of several components, the earliest of which decreased in latency as the stimulated site moved rostrally, ranging from 46 msec for stimulation of the gastrocnemius, to 14 msec for stimulation of the deltoid. Experiments were performed to distinguish the mechanisms by which magnetic stimulation of the muscle was effective in evoking these cerebral potentials. For the gastrocnemius, the intensity of the magnetic stimulus needed for evoking cerebral potentials was less than that required for activating mixed or sensory nerves in proximity to the muscle belly (eg, posterior tibial nerve in the popliteal fossa, sural nerve at the ankle). Vibration of the muscle or passive lengthening of the muscle, procedures which activate muscle spindles, were accompanied by a significant attenuation of the potentials evoked by magnetic stimulation of the muscle. Anesthesia of the skin underlying the stimulating coil had no effect on the latency or amplitude of the early components of the magnetically evoked potentials, whereas electrically evoked potentials from skin electrodes were abolished. Thus, the cerebral potentials accompanying magnetic stimulation of the muscle appear to be due to activation of muscle afferents. We suggest that magnetic stimulation of muscle can provide a relatively simple method for quantifying the function of muscle afferents originating from a wide variety of skeletal musculature.

Seismic communication in the blind subterranean mole‐rat: patterns of head thumping and of their detection in the Spalax ehrenbergi superspecies in Israel

Patterns of seismic communication and somatosensory responses were studied in four chromosomal species (2n= 52, 54, 58, 60) of blind subterranean mole‐rats, belonging to the Spalax ehrenbergi superspecies in Israel. The patterns involved head thumping signals and surface‐recorded cerebral potentials evoked by vibrational signals. The patterns correspond to the differences in territory size and population density which characterize the four species. It is suggested that this correspondence is related to the adaptive significance of the seismic communication.

The cortical drive to human respiratory muscles in the awake state assessed by premotor cerebral potentials.

1. We investigated the possibility of a cortical contribution to human respiration by recording from the scalp of awake subjects the premotor cerebral potentials that are known to precede voluntary limb movements. 2. Electroencephalographic activity (EEG) was recorded from scalp electrodes and averaged for 1.8-2.0 s before the time at which airway pressure exceeded an inspiratory or expiratory threshold. Clear premotor cerebral potentials were recorded during brisk, self-paced nasal inhalations or exhalations. In ten subjects, a slow cortical negativity (Bereitschaftspotential) was apparent in the averaged EEG, commencing 1.2 +/- 0.3 s before the onset of inspiratory (scalene) or expiratory (abdominal) muscle activity (EMG). It was maximal at the vertex, with a mean slope of 12.3 +/- 5.8 microV/s, and was followed by a post-movement positivity. 3. In four subjects the inspiratory premotor potential culminated in a large negativity, the motor potential, which began 24 +/- 15 ms before the onset of scalene EMG. It is argued that such a short latency is consistent with a volitionally generated respiratory command which travels relatively directly to the respiratory muscles, having a total central delay which is no longer than that for voluntary finger movements. 4. That the respiratory premotor and motor potentials did not originate in subcortical structures was supported by their absence in a patient suffering from chronic reflexogenic hiccups, in whom cerebral activity was back-averaged from each brisk hiccup. 5. During quiet breathing, in which subjects were relaxed and distracted from thinking about their respiration, no premotor cerebral potentials preceding inspiration could be detected. This failure was not due to the slow rate of rise of inspiratory activity during quiet breathing as compared with a brisk sniff, because premotor potentials were detected when subjects intermittently generated slow active expiratory efforts. 6. These observations suggest that during quiet breathing the cerebral cortex does not contribute to respiratory drive on a breath-by-breath basis. Conversely, the presence of clear premotor cerebral potentials when subjects performed self-paced inspiratory or expiratory manoeuvres illustrates the powerful cortical projection to human respiratory muscles.

Laser-evoked brain potentials in patients with dissociated loss of pain and temperature sensibility

Brief heat stimuli, elicited by a CO2 laser (10.6 μm wave length), activate the most superficial cutaneous nerve terminals of the thin myelinated Aδ and unmyelinated C fibres which mediate heat and pain sensations. This paper investigates late cerebral potentials (SEPs) in response to laser pulses in comparison with those to conventional electrical stimulation in 18 patients with a dissociated sensory deficit (intact mechanosensibility and disturbed temperature and pain sensation). Patients were stimulated in the most disturbed limb (affected area) and in a corresponding control area.In all 18 patients the SEPs elicited by laser stimuli were able to identify the body site with heaviest disturbances in pain and thermosensibility: the SEPs from the affected area were reduced or delayed, compared to the control area. In contrast, no alterations in SEPs could be observed after conventional electrical nerve stimulation, in agreement with the normal mechanosensibility. However, the degree of SEP modulation in response to cutaneous heat stimuli did not correspond to the severity of the subjectively reported sensory deficit. Highest correlations between sensory deficits and abnormal SEPs were found in all those patients in whom computer tomography or MR imaging documented a localized destructive process in the CNS. All patients with the smallest SEP modulations despite a considerable sensory deficit had an inflammatory aetiology. Preliminary criteria to define a laser-evoked SEP as pathological are discussed.

Influence of an acoustic preparatory signal on postural reflexes of the distal leg muscles in humans

In standing subjects the sudden displacement of a platform toe-up evokes a stabilizing postural response of the anterior tibial muscle (long-latency reflex). A preparatory signal (acoustic warning stimulus) preceding the postural perturbation by 1 s results in a significant decrease in latency of this long-latency response. There is no parallel modulation of the afferent cortical input in terms of evoked cerebral potentials following platform tilts toe-up nor of efferent cortico-spinal functions as evaluated by means of transcranial magnetic stimulation. Conceivable underlying mechanisms include faster intraspinal and/or intracortical processing of afferent input or switching to a shorter spinal reflex pathway.

CEREBRAL POTENTIALS EVOKED BY PAINFUL LASER STIMULI IN PATIENTS WITH SYRINGOMYELIA

Brief cutaneous heat stimuli generated by a CO2 laser were used to elicit late somatosensory evoked cerebral potentials (SEPc) in 10 patients with syringomyelia. For comparison, early and late cerebral potentials in response to electrical nerve stimuli (SEPn) were recorded in the same session. In 8 patients with localized impairment of pain and temperature sensitivity we found complete absence of SEPc after stimulation of the affected area; in another patient with similar sensory deficits, the SEPc was grossly attenuated and delayed. In 1 patient with intact pain sensitivity but absent temperature sensitivity, a well defined SEPc could be recorded. Both early cortical SEPn and late SEPn in response to conventional nerve stimuli were normal in all patients and thus did not differentiate control and affected areas. These data indicate that alteration of SEPc correlates with altered pain sensitivity in patients with a circumscribed spinal lesion. SEPc may thus be used as a neurophysiological test in the assessment of hypalgesic dermatomes.

Comparison in postnatal development between somatosensory and motor conduction in rabbits

A comparative study between the somatosensory-evoked cerebral potential (SEP) and motor cortex-evoked muscle response (MEMR), and between the sensory nerve action potential (SNAP) and peripheral nerve-evoked muscle response (M wave) was performed with respect to their maturational changes in the peak latencies, using 24 rabbits of ages of 10 to 180 days. The peak latencies of SEP, MEMR, SNAP and the M wave all decreased with an increase in age according to a hyperbolic curve of y = axb + c (b less than 0). The adult values of the peak latencies were reached simultaneously at 80 days of age for SEP and MEMR, and at 60 days of age for SNAP and the M wave. These findings indicate that the conduction of the somatosensory and motor pathways becomes fully maturated at the same time. On analysis of the differential coefficients on the above equation, some but substantial differences in the decrease rate of the peak latency were also found between SEP and MEMR, and between SNAP and the M wave. This suggests that there are also some differences in the maturational rate between the two pathways.

Cerebral potentials evoked by esophageal distension in human

Recent studies have shown that cerebral evoked potentials (EPs) can be recorded after balloon distension of the human esophagus. The aim of this study was to evaluate the characteristics of these viscerosensory EPs and to investigate the relations between these EPs and perception of esophageal distension. Nineteen healthy volunteers (22-60 yr old) were studied. A balloon positioned 5 cm above the lower esophageal sphincter was inflated 10 times each minute. EPs recorded from four midline scalp electrodes were averaged for 50 and 100 inflation cycles. A clearly defined triphasic (negative-positive-negative) EP was recorded in all subjects and from all four recording sites when a volume leading to definite sensation and rapid balloon inflation (170 ml/s) was used. The latencies of the peaks were 231 +/- 7 (N1), 303 +/- 7 (P1), and 379 +/- 8 ms (N2). No significant correlation between stimulus perception and latency was found. The amplitude and quality of the EPs (scored by 3 blinded observers) increased significantly (P less than 0.01, ANOVA) with increasing sensation. Slow balloon inflation (30 ml/s) was significantly less effective in evoking EPs than rapid inflation (P less than 0.01). The EPs evoked by 100 inflations were not significantly clearer than those evoked by 50 inflations. It is concluded that the ability to record cerebral potentials evoked by esophageal balloon distension is related to the rate of balloon inflation and to the level of awareness of the stimulus.

The Use of Single Event Evoked Cerebral Potentials to Predict Stimulus Identifications

An experiment was conducted to determine the feasibility of using waveform features of the single trial transient evoked cerebral potential as a predictor of a simple “YES or NO” decision response. Six subjects, who were tested in a stimulus identification test, were shown a 100-trial sequence of instruction stimulus sets to which they decided by a button push whether the stimulus agreed with the instruction. The Electroencephalogram (EEG) was recorded during the test, along with a stimulus trigger pulse used to align the EEG with the stimulus. The coefficents of a Linear Predictor Coding model fit to the post-stimulus, evoked potential signals were used as inputs for training and testing a supervised, hidden layer, neural network representation of the decisionmaking process. The resultant error rate computed using the “leaving one out” procedure, varies from 32-% to 46-% for predicting the decisions made by the subjects.

Cerebral potentials evoked by fast head accelerations

Fast, time optimal, voluntary horizontal head rotations produce evoked cerebral potentials (EPs). These show distinct amplitudes between 10 and 25 microV and latencies of N1 66 ms, N2 178 ms, P1 295 ms and N3 424 ms. Specifically, an increase in head acceleration is significantly correlated with a decrease of the latency of the EPs and an increase in their normalized amplitude. Control studies with isolated proprioceptive stimulation of the wrists and the neck with the head fixed provided evidence for the dominant vestibular generation of the head movement associated EP that is fine tuned throughout changes in head acceleration.

Modulation of Pain-Related Somatosensory Evoked Potentials by General Anesthesia

The aim of the present study was to assess if late somatosensory evoked cerebral potentials (SEPs) in response to painful electrical stimuli are a sensitive indicator for analgesic treatment during general anesthesia. For this purpose, a pain model developed for the quantification of drug-induced analgesia in awake volunteers was used in 10 patients scheduled for elective abdominal hysterectomy. Before induction of anesthesia, stimuli were adjusted to two and three times the pain threshold for each individual. Late auditory evoked potentials (AEPs, 30 dB hearing level) and spontaneous electroencephalogram were also evaluated. After control recordings, anesthetic treatments were varied in the following sequences: (a) 0.8% (end-tidal) halothane with 70% nitrous oxide (HN); (b) 0.8% halothane in oxygen (H1); (c) same anesthetic condition as in H1, but the SEP and AEP stimulus intensities were increased to 15 times pain threshold and to 70 dB hearing level, respectively (H2); and (d) fentanyl (0.25 mg) was given with 0.8% halothane in oxygen with no further change in stimulus intensities (HF). In treatments HN and H1, blood pressure and heart rate increases to pain stimuli were abolished, and SEPs and AEPs were both suppressed. Increasing the somatosensory stimulus intensity (treatment H2) stimulated heart rate and arterial pressure responses and again elicited the SEPs. However, AEP components remained suppressed with increased auditory stimulus intensity. Addition of fentanyl (HF) suppressed SEP amplitudes and stimulus-induced hemodynamic responses. Our results suggest that late SEPs in response to painful stimuli change with different analgesic levels.

Laboratory pain and cerebral potentials

Laboratory pain and cerebral potentials

Are Gender Differences in Schizophrenia Reflected in Brain Event-related Potentials?

Numerous studies have reported relationships between gender and cerebral event-related potentials (ERPs) recorded from the human scalp. Recent studies have suggested that the influences of gender on ERPs may differ in persons with schizophrenia compared to healthy controls. In a further evaluation of the influences of this critical subject variable on ERP characteristics in schizophrenia, ERPs of age- and gender-matched groups (n = 72 each) of unmedicated schizophrenic patients and healthy controls were compared. ERPs elicited by left and right median nerve stimulation, checkerboard pattern visual flash, and auditory clicks were recorded from 15 scalp leads. The results confirm previous findings showing that: (1) number of comparable gender effects present in the ERP records of these two large study groups and (2) specific Diagnosis x Gender interactions suggesting that schizophrenic illness may modify normal gender influences on ERP characteristics. These data illustrate the point that matching schizophrenic patients and healthy control populations for gender is essential but not sufficient. Even in carefully matched groups, gender confounding can persist as a source of error variance because the influence can vary for different diagnostic groups.

Time and tiles on the brain

Both the quasicrystalline appearance of mammalian cerebral cortex and the quasiperiodicity of mammalian cerebral compound field potentials (EEG/ERBP) have long been noted. A recent experiment claims to show the eigenvalue spectrum of a quasiperiodic tiling of coupled oscillators in the plane; and this spectrum of resonant frequencies has some analogies with that of mammalian EEG/ERBP. Concurrently, Connectionist literature now admits the significance of internally generated network rhythmicity in Non-Lipschitzian neurodynamics. It may be time to test the hypotheses of: (a) quasi-crystalline icosahedral symmetry of neocortical architectonics and (b) some fractal characteristics of EEG/ERBP under behavioral conditions.

Assessment of pain in the elderly using event-related cerebral potentials

Assessment of pain in the elderly using event-related cerebral potentials

Functional monitoring of pain and temperature sensitivity in patients with syringomyelia by CO 2—Laser evoked cerebral potentials

Functional monitoring of pain and temperature sensitivity in patients with syringomyelia by CO 2—Laser evoked cerebral potentials

Cerebral potentials evoked by electrical nerve and cutaneous heat stimuli in patients with dissociated sensory loss

Cerebral potentials evoked by electrical nerve and cutaneous heat stimuli in patients with dissociated sensory loss

Spectral analysis and mathematical modeling of electrical cerebral activity in rats with genetically determined predisposition to seizure and in controls

Spectral signs of genetically determined predisposition to seizure characteristic of Krushinskii-Molodkina (KM) strain rats were found when studying summated cerebral potentials, namely increased power of low (1–3 Hz) frequencies in spectra of motor and visual cortex potentials together with an abrupt increase and a reduction respectively in the power of hippocampal and caudate nucleus potentials. Comparative spectra of summated electrical activity within neuronal networks [10] and those of experimentally obtained potentials as determined by modeled parameters simulating neuronal networks were found (an inverse problem of modeling). It was found that spectral signs of predisposition to seizure could reflect changes in the physiological properties of neuronal networks belonging to the rat brain structures investigated. It might be suggested on the basis of the calculations performed that genetic predisposition to seizure in KM strain rats is determined by attenuation of the inhibitory function of the caudate nucleus and by heightened excitability (reactivity) in neurons of the paleo- and neocortex.

Laser-evoked cerebral potentials and sensory function in patients with central pain

Laser-evoked cerebral potentials and sensory function in patients with central pain