Differences in human evoked potentials related to olfactory or trigeminal chemosensory activation

The aim of the present study was to determine, whether there are differences in the topographical distribution of chemosensory evoked potentials (CSEPs) due to stimulation with different odous substances. The odorants used in the study which mainly excited the olfactory nerve were vanillin and acetaldehyde; those which additionally excited the trigeminal nerve were sulphur dioxide and ammonia. Twelve subjects participated in the study. The subjects separately estimated the intensity of the odorous and of the painful/pricking sensation caused by the stimuli, and described the odorous qualities in their own words. CSEPs were recorded from 7 positions.After stimulation with “olfactory” subsances maximum CSEP amplitudes were recorded at parietol-central sites, and after stimulation with “trigeminal” substances maximum amplitudes were obtained at the vertex. Following stimulation with ammonia and sulphur dioxide amplitudes were largest contralateral to the stimulated nostril. In contrast, little difference in CSEP amplitudes was observed between hemispheres after stimulation with vanillin or acetyldehyde.Thus, the topographical distribution of CSEP amplitudes may provide information with regard to the sensory system (olfactory or trigeminal) activated by the presentation of an odorous stimulus.     

Differences in human chemosensory evoked potentials to olfactory and somatosensory chemical stimuli presented to left and right nostrils

The aim of the present study was to determine whether the recordingof chemosensory evoked potentials (CSEP) in healthy subjects(n = 11) can be helpful in differentiating the olfactory ortrigeminal component possessed by odorants. By recording fromseveral positions on the surface of the skull it was attemptedto ascertain whether different generators are responsible forCSEP associated with the different sensory components of odorants.Birhinal stimulation was used in order to establish an interactionbetween the stimulated side and the stimulated sensory channel.The four substances carbon dioxide, menthol, hydrogen sulphideand vanillin were tested. EEG was recorded from eight positions. The CSEPs' topographical distribution revealed differences inthe location of maximum amplitudes following stimulation withdifferent types of stimulants. Largest amplitudes always appearedat the vertex when trigeminal stimulants (menthol, carbon dioxide)were presented, whereas olfactory substances (vanillin, hydrogensulphide) elicited maximal amplitudes at parietal and centralsites. This suggests that at least two neuronal populationsare involved in the cortical generation of CSEP. Another interestingfinding was that the evoked potentials differed in relationto the stimulated side. Generally, responses to carbon dioxide,menthol and hydrogen sulphide had shorter latencies and smalleramplitudes after stimulation of the left nostril. In contrast,after stimulation with vanillin latencies were shorter and amplitudestended to be smaller after stimulation of the right side. Sincevanillin was the only substance which always evoked pleasantand positive associations, it was assumed that the differencesin CSEP after stimulation of the two nostrils are related tothe different processing of emotional information within thetwo hemispheres.     

Cerebral evoked potentials after rectal stimulation

We obtained reproducible cortical evoked potentials (EPs) in response to electrical stimulation of the rectum with 1 Hz frequency. We found 2 distinctly different EPs in response to rectal stimulation. In 5 females, the EP had an early onset latency (mean 26 msec) with multiple positive and negative peaks. In 10 females, the EP had a later onset latency (mean 52 msec) and a trifid configuration, having a very prominent negative peak. The early onset EPs after rectal stimulation appeared very similar to the wave form of the cortical EPs recorded after pudendal nerve stimulation. Finding similar interpeak latencies in the early onset EP after rectal stimulation and the EP after pudendal nerve stimulation suggests that either the same pathway was used or that rectal stimulation also stimulated the pudendal nerve. It appears that we stimulated visceral afferents when we recorded late onset EPs, because the large EP amplitude declined rapidly with faster stimulation rates and also with greater number of averaging, and the sensation threshold was very unstable, all different to somatosensory EPs.     

Somatosensory evoked potentials (SEPs) elicited by magnetic nerve stimulation

Magnetic stimulation of peripheral nerves at distal and proximal sites of the upper and lower extremities and at the midlumbar level were used to elicit cortical somatosensory evoked potentials. Evidence is provided that peripheral nerve trunks, rather than distal receptor afferents, are the anatomical structures stimulated by the electromagnetic fields. Magnetic stimulation of peripheral nerves is considered to be useful for an evaluation of the integrity of proximal nerves, nerve roots and central conduction along sensory pathways. In contrast to electrical nerve stimulation, magnetic stimulation is painless and can be applied to proximal nerves and plexus. By means of proximal nerve stimulation central sensory conduction can be tested even in patients with peripheral nerve lesions or polyneuropathy.     

Somatosensory evoked potentials elicited by dorsal penile and posterior tibial nerve stimulation

SEPs were elicited by stimulation of the dorsal penile nerve (DPN) or posterior tibial nerve (PTN) under 3 conditions of stimulation: random and constant interstimulus intervals, and subject-initiated stimulation. Within these conditions, the effects of repeated stimulation were also examined. The latency of the N90 peak decreased with repeated stimulation. N90 amplitude decreased with increased foreknowledge as well as with repeated stimulation. Factors extracted by principal components analysis revealed similar effects. A difference between DPN and PTN stimulation was seen in a factor associated with the N90 peak, wherein the condition involving subject self-initiation of the stimulus reflected a significantly greater decrease in SEP amplitude when the DPN was stimulated. Morphological commonalities were observed in the SEPs elicited by DPN and PTN for a given subject.     

Chemo-somatosensory event-related potentials in response to repetitive painful chemical stimulation of the nasal mucosa

The aim of the study was to investigate how chemo-somatosensory event-related potentials (CSSERPs) and pain ratings are modified by repetitive painful stimulation of the nasal mucosa (58% v/v CO₂, 200 msec duration). Twenty-two subjects performed 3 experiments during which trains of stimuli were applied. The interstimulus interval (ISI) between stimuli was constant for each experiment, but varied between experiments (8, 4, and 2 sec). CSSERPs were obtained from positions (Fz, C3, Cz, C4, and Pz). The subjects not only rated the overall perceived intensities but also reported the quality of the stimuli. At an ISI of 8 sec estimates decreased and only stinging sensations were reported. In contrast, at an interval of 2 sec estimates increased being accompanied by the buildup of burning pain. This phenomenon was interpreted in terms of the superposition of first (sharp and stinging pain: Aδ fibers) and second pain (dull and burning pain: C fibers), respectively. However, given the special circumstances of short ISIs CSSERP amplitudes decreased the more the shorter the ISI was. In line with previous investigations it is hypothesised that CSSERPs predominantly reflect nociceptive information transmitted via Aδ fibers.     

Cerebral cortical respiratory-related evoked potentials elicited by inspiratory occlusion in lambs.

Respiratory-related evoked potentials (RREP) elicited by inspiratory mechanical loads have been recorded in humans. Early RREP peaks were hypothesized to be generated by activation of neurons in the somatosensory cortex. An animal model was developed to test this hypothesis in chronically instrumented, awake, spontaneously breathing lambs. Electrocorticogram (ECoG) was recorded bilaterally with ball electrodes on the dural surface over the somatosensory region. Inspiratory occlusions were presented through a face mask or endotracheal tube as interruptions of inspiration. Occlusion-elicited evoked potentials were obtained by computer-signal averaging the ECoG activity. A short-latency positive peak was observed bilaterally in the averaged occlusion-elicited evoked potentials in all animals breathing with the facemask and 5 of 8 lambs with the endotracheal tube. Postmortem identification of the electrode location demonstrated that the ECoG was recorded in the caudal-lateral portion of the somatosensory cortex. These results demonstrate that inspiratory occlusion elicits an evoked potential in the somatosensory cortical region of awake, spontaneously breathing lambs. The lamb cortical RREP is similar to human RREP.     

Comparison of short-latency trigeminal evoked potentials elicited by painful dental and gingival stimulation

Painful stimulation of tooth pulp and of the maxillary gingiva was undertaken in 16 volunteers. Short-latency evoked potentials (15–20 msec) were recorded over 800 trials in each case at F3-P3 of F4-P4, and the resultant averaged wave forms were compared. The gingival wave was distinct in all subjects and could be averaged across subjects while the dental waves were either noise or very inconsistent over subjects. Averaging of the dental wave forms across subjects yielded an uninterpretable result. It was clear that dental evoked potentials could not be recorded at these sites. These findings could be explained by either or both of two hypotheses: (1) dental afferents are predominantly small fiber, nociceptive end organs that conduct more slowly than soft tissue afferents whereas gingival stimulation activates both large and small fiber populations; and (2) dental representation in somatosensory cortex is different and phylogenetically more primitive than that of neighboring soft tissue. Therefore, the location of the generator sites in cortex and the orientation of the dipole may be different for dental than for gingival wave forms.     

Effects of electrical stimulation of the human olfactory mucosa

Electrical stimulation of the human olfactory mucosa was performed by means of an electrode attached to a rhinoscope . Stimulation of the nasal mucosa did not evoke smell sensations, but suppressed smell sensations of presented odorants. When electrical stimulation followed the exposure to an odorant within a certain interval, the stimulus recalled the already faded sensation of the preceding odorant. Electrical stimulation without prior natural stimulation produced unpleasant sensations in 3 patients with a history of temporal lobe seizures and olfactory auras , but not in patients with primary, generalized or focal epilepsy.     

Cerebral evoked potentials after stimulation of the posterior urethra in man

Cerebral evoked potentials (EPs) were recorded in 25 neurologically normal subjects aged 22–73 years (mean 44.0) after stimulation of the posterior urethra (PU) and the pudendal nerve. After maximal PU stimulation 2 different configurations of the potential were found. In 12 cases a simple bi-triphasic wave form was recorded while in 12 cases there was a bifid form of the first negative wave. In 1 case identical EPs were recorded after PU and pudendal nerve stimulation.It was concluded that (1) PU stimulation excites fibres in the pudendal nerve at higher stimulation strength, resulting in a bifid wave form of the cerebral evoked potential in some individuals, (2) the most prominent negative peak, N1, with a latency of 102.1 ± 13.2 msec, is the most reproducible part of the PU-evoked potential, (3) the N1 is probably transmitted through Aδ fibres localized in the pelvic nerves, (4) there are differences between individuals concerning pudendal and pelvic nerve involvement in afferent innervation of the urethra.     

Visual evoked potentials elicited by a moving unidimensional noise pattern

(1) Motion onset and offset visual evoked potentials (VEPs) were recorded in normal human subjects using a unidimensional noise pattern moving at 1, 8 and 64°/s. The maximum N1-P1 amplitude of the motion onset response was obtained when using a fine noise pattern (maximum energy at 5.2 cpd) moving at 8°/s. (2) At a velocity of 8°/s, the motion onset response (fine pattern, 0.70 contrast) showed a morphology similar to the pattern disappearance response. Both at a lower (1°/s) and a higher velocity (64°/s) the N1-P1 amplitude of the motion onset complex was significantly reduced. The latency of the motion onset response (8°/s) and the pattern disappearance complex were significantly different. (3) The effect of lowering the spatial content of the noise pattern on the amplitude of the motion onset response was different for the 3 velocities tested: the largest effect was at the lower velocity of 1°/s; there was no similar effect on the pattern disappearance response. (4) With decreasing contrast, the N1-P1 amplitude of the motion onset response at 8°/s decreased, but this reduction in amplitude was much less than that of the disappearance response. The contrast dependency of the motion onset complex was identical for binocular and monocular recordings. (5) Increasing the motion duration or the duration of the interstimulus interval did not alter the general morphology of the motion response.     

Distribution of evoked potentials on stimulation of the human pulvinar.

The distribution of the evoked cortical potentials recorded during stereotactic pulvinectomy is analyzed. The evoked cortical potential shows maximal amplitude in the precentral area, with decreasing amplitude in the parietal and anterior temporal area, and minimal amplitude in the occipital area. The pulvinar has been histologically considered to have dense connections with the parietal lobe and no connection with the frontal lobe. However, our results suggest that the pulvinar has a dense functional connection with the frontal cortex, through which the pulvinar plays a role in motor function.     

Cerebral potentials evoked by rectal distention in humans

The afferent pathways from the rectum can be stimulated and studied after mechanical distention of the rectum. We studied the rectum-brain axis in 24 healthy young adults. The rectum was stimulated with a rectal balloon using inflation volumes of 10 ml and 30 ml air at a stimulation frequency of 0.167 Hz. Additional studies were carried out with 20 ml distention volumes, random stimulation frequency, and stimulation rates of 0.08 Hz and 0.017 Hz. We found two different cortical EPs. An early onset EP was present in 21 of the 24 subjects. P1 latency shortened significantly with increasing distention volumes, but peak amplitudes did not change significantly with larger distention volumes. A late onset EP was present in all subjects with NI latency of 210 ± 15 msec, PI latency of 316 ± 24 msec, and NII latency of 444 ± 34 msec. The different EPs could be due to stimulation of two different visceral afferent pathways which are present in the same individual, due to stimulation of two different fiber populations or due to simultaneous stimulation of afferents in surrounding structures. EP recording after rectal stimulation might be useful in future studies of patients with abnormal rectal sensation.     

Suggestions for collection and reporting of chemosensory (olfactory) event-related potentials

Chemosensory event-related potentials hold great promise forfurthering the understanding of the olfactory system, the processingof olfactory information, and disease processes affecting olfaction.Collection of this type of data has been difficult and suggestionsare presented to aid investigators new to this field. Suggestionsfor nomenclature, recording parameters, chemosensory stimulationparameters and reporting conventions are discussed. Also discussedare the future directions of this field and the current needsregarding the development of a normative database.     

Bovine olfactory and nasal respiratory epithelium surfaces

Summary High-voltage transmission electron microscopy and cryo-ultramicrotomy together with scanning electron microscopy and some conventional transmission electron microscopy of ultrathin sections have been applied to the mucous surfaces of bovine olfactory and respiratory epithelia. Distal segments of olfactory cilia tend to run in parallel and could be followed over distances up to about 30 m using high-voltage electron microscopy. This technique and scanning electron microscopy showed that on average 12–13 of such cilia could be observed per nerve ending. After correction for obscured cilia this number becomes about 17. High-voltage micrographs and micrographs made from sections prepared with a cryo-ultramicrotome showed the presence of electron-lucent pockets inside the olfactory mucus. The latter technique also showed that the mucus itself is not fibrous, but rather a continuum varying in electron density. The mucus layer contains various granular structures. Ciliary and microvillar membranes appear thicker with cryo-ultramicrotomy than when the sections are prepared with conventional techniques. The cores of the axonemal microtubules in olfactory as well as in respiratory cilia are darkly stained with this technique. Vesicles present inside the nerve endings are also darkly stained. Dimensions and some other numerical values of interest in olfaction are presented.     

Somatosensory evoked potentials by tibial nerve stimulation in the rabbit

Somatosensory evoked potentials by tibial nerve stimulation were obtained in ten New Zealand rabbits. The subcortical or cortical source of the three negative and three positive peaks present in the first 55 ms is discussed viewing the results obtained by different surface electrode locations and by stereotaxic recordings. The authors report interanimal, interhemispheric and test-retest variability of latencies and amplitudes of subcortical and cortical components.     

Laminar analysis of hippocampal potentials evoked by peripheral stimulation

From areas SA₁ and SA₂ of the dorsal hippocampus of unanesthetized rabbits immobilized with d-tubocurarine a laminar analysis was made of evoked potentials (EP) in response to stimulation of the sciatic nerves. Inversion of the initial surface-positive phase of the EP was observed at the level of the pyramidal layer. The subsequent surface-negative phase reached a maximum value in the layer of basal dendrites of the pyramidal cells. The initial portion was inverted somewhat above the pyramidal layer and reached its maximum value approximately at the boundary of the pyramidal and radial layers. The change in sign of the remaining portion of this component occurred 0.3–0.4 mm deeper than the pyramidal layer. It is suggested that both components of the EP picked up from the hippocampal surface are due to an excitatory postsynaptic potential (EPSP) at the apical (positive phase), and basal (negative phase) dendrites. The positivity in the region of the pyramidal somata appears to be an extracellular reflection of a composite postsynaptic potential (IPSP) generated in this region.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 4. pp. 434–438, July–August, 1970.