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PubMed1984

Event-related potentials recorded from the scalp and nasopharynx. I. N1 and P2.

Event-related potentials were recorded from the scalp and nasopharynx during a signal-detection task. These responses were evaluated with respect to the effects of interstimulus interval, intensity, frequency, attention and modality. Our results indicate the existence of at least 4 distinct processes occurring in the 75-150 msec latency range following auditory stimuli. The first process is indexed in the vertex-N1b/temporal-N1a component. This component does not reverse in polarity below the sylvian fissure and is not seen in nasopharyngeal recordings. The location of its generator is not known. Probably there are two or more sources active at this latency. The second process finds reflection in the N1c/PgP120 component. This component is recorded with maximum amplitude on the side contralateral to the ear of delivery. A source in the lateral surface of the temporal lobe is a likely generator. The third process corresponds to Wolpaw and Penry's (1975) Ta positivity. How much of this represents the underside of a vertically oriented dipole and how much a surface positivity is unknown. Finally, during attention, a lateralized processing negativity seems to overlap these components at the scalp, but not at the nasopharynx. The auditory vertex N1 peak is quite distinct from the visual N1 which is more posteriorly recorded on the scalp and which is associated with a definite nasopharyngeal positive wave. The P2 peak is quite similar across auditory and visual modalities. In both modalities it is maximally recorded from the vertex and has no nasopharyngeal concomitant.

Adult↗
PubMed1985

Early evoked potentials detected from the scalp of man following infraorbital nerve stimulation.

Stimulation of the infraorbital nerve evoked a short latency scalp response characterized by a large amplitude triphasic potential (W1), followed by two smaller negative deflections (W2 and W3). All these waves were presynaptic in origin (as shown by double pulse stimulation), but appeared to be generated by separate dipoles. Short distance bipolar recording showed that W1 travelled from the zygoma to the mastoid. This wave was thought to be generated in a nearby neural structure, presumably the proximal part of the maxillary nerve, the gasserian ganglion and possibly even the trigeminal root. W2 and W3 components were probably generated by the trigeminal root fibres running through the brain-stem. Their origin from slowly conducting trigeminal fibres was ruled out by their absence in short distance bipolar records along the line from the zygomatic bone to the mastoid process, and by studies on their thresholds, which were shown to be identical to those of W1. Control experiments with concurrent facial muscle recording excluded any possible contamination of the scalp response to infraorbital nerve stimulation by electromyographic activity, and demonstrated gross muscular artefacts, picked up as far-field activity by scalp electrodes, following electrical stimulation of the upper lip.

Adult↗
PubMed1987

Somatosensory evoked potentials from the thalamic sensory relay nucleus (VPL) in humans: correlations with short latency somatosensory evoked potentials recorded at the scalp.

Somatosensory evoked potentials (SEPs) were recorded in humans from an electrode array which was implanted so that at least two electrodes were placed within the nucleus ventralis posterolateralis (VPL) of the thalamus and/or the medial lemniscus (ML) of the midbrain for therapeutic purposes. Several brief positive deflections (e.g., P11, P13, P14, P15, P16) followed by a slow negative component were recorded from the VPL. The sources of these components were differentiated on the basis of their latency, spatial gradient, and correlation with the sensory experience induced by the stimulation of each recording site. The results indicated that SEPs recorded from the VPL included activity volume-conducted from below the ML (P11), activity in ML fibers running through and terminating within the VPL (P13 and P14), activity in thalamocortical radiations originating in and running through the VPL (P15, P16 and following positive components) and postsynaptic local activity (the negative component). The sources of the scalp-recorded SEPs were also analyzed on the basis of the timing and spatial gradients of these components. The results suggested that the scalp P11 was a potential volume-conducted from below the ML, the scalp P13 and P14 were potentials reflecting the activity of ML fibers, the small notches on the ascending slope on N16 may potentially reflect the activity of thalamocortical radiations, and N16 may reflect the sum of local postsynaptic activity occurring in broad areas of the brain-stem and thalamus.

Electroencephalography↗
PubMedDate not supplied

Short latency somatosensory evoked potentials following mechanical taps to the face. Scalp recordings with a non-cephalic reference.

Trigeminal somatosensory evoked potentials were recorded over the scalp using non-cephalic reference sites following mechanical taps to the face. A negative wave form, Nf17, was recorded bilaterally with its highest amplitude over the frontal scalp contralateral to the side of stimulation. A localized negative wave form, Np25, was recorded over the centro-parietal scalp contralateral to the side of stimulation. Np25 had an onset latency of 16.46 msec. The location and restricted spatial distribution of Np25 suggest that it represents the initial activation of the face area of the primary sensory cortex. The widespread bilateral nature of Nf17 and its latency of onset preceding that of Np25 suggest that Nf17 may be a 'far-field' potential reflecting activity in subcortical sensory pathways subserving the face.

Adult↗
PubMed1995

Cervical and scalp recorded short latency somatosensory evoked potentials in response to epidural spinal cord stimulation in patients with peripheral vascular disease.

Somatosensory evoked potential (SEP) studies were performed in 14 patients with peripheral vascular disease who received epidural spinal cord stimulation (SCS) for chronic pain relief of the lower limbs. Signals were amplified and filtered between 20-2000 Hz and 200-2000 Hz to better identify activities in the high frequency range. In 7 patients bit-colour maps were also computed. In all the patients a homogeneous short-latency scalp evoked potential with a prevalent diphasic shape (P1-N1) was recorded. In all our scalp records, even with the wide bandpass, small short-latency positive deflections were observed on the descending front of the first major positive wave and they were better defined as a series of up to 6 wavelets, preceding the major negative scalp wave in the tracings filtered through the narrow bandpass. They appeared in an interval ranging from 5.5 to 15.6 msec. Bit-colour maps showed consistent positive fields, with a maximum at the vertex, starting mainly at about 5.5 msec; in 3 patients, a prominent positivity between 8.5 and 10.5 msec was recorded followed by smaller components preceding the major positive-negative (P1-N1) complex. More synchronous volleys during direct SCS produced clear short-latency SEPs. Although they were of larger amplitude, we regarded them as corresponding to those described by previous authors obtained by stimulation of nerves of the lower limbs, and probably arising from subcortical structures.

Adult↗
PubMed2005

Coherence and phase locking in the scalp EEG and between LORETA model sources, and microstates as putative mechanisms of brain temporo-spatial functional organization.

Brain electric mechanisms of temporary, functional binding between brain regions are studied using computation of scalp EEG coherence and phase locking, sensitive to time differences of few milliseconds. However, such results if computed from scalp data are ambiguous since electric sources are spatially oriented. Non-ambiguous results can be obtained using calculated time series of strength of intracerebral model sources. This is illustrated applying LORETA modeling to EEG during resting and meditation. During meditation, time series of LORETA model sources revealed a tendency to decreased left-right intracerebral coherence in the delta band, and to increased anterior-posterior intracerebral coherence in the theta band. An alternate conceptualization of functional binding is based on the observation that brain electric activity is discontinuous, i.e., that it occurs in chunks of up to about 100 ms duration that are detectable as quasi-stable scalp field configurations of brain electric activity, called microstates. Their functional significance is illustrated in spontaneous and event-related paradigms, where microstates associated with imagery- versus abstract-type mentation, or while reading positive versus negative emotion words showed clearly different regions of cortical activation in LORETA tomography. These data support the concept that complete brain functions of higher order such as a momentary thought might be incorporated in temporal chunks of processing in the range of tens to about 100 ms as quasi-stable brain states; during these time windows, subprocesses would be accepted as members of the ongoing chunk of processing.

Brain↗
PubMed2005

Hemispheric lateralization of voice onset time (VOT) comparison between depth and scalp EEG recordings.

Auditory-evoked potential (AEP)s elicited to French-language voiced stop consonant (/ba/) and voiceless stop consonant (/pa/) were studied in non-language-impaired epileptic patients and non-epileptic volunteers. First, depth AEPs recorded from the primary auditory cortex during pre-surgical exploration and scalp AEPs recordings using high resolution EEG (HR EEG-64 channels scalp EEG) were compared in the same patients. Both methods indicated that the processing of voiced and voiceless consonants was based on a temporal auditory coding. /Ba/ elicited a first complex (N1) at the onset of voicing and a second component [release component (RC)] time-locked to release. This processing took place specifically in the left primary auditory cortex. Source modeling of the RC showed that a left-greater-than-right amplitude of source probes (SP) both in epileptic patients with left-hemispheric language dominance [established by means of invasive tests (WADA test) and/or clinical data] and right-handed non-epileptic subjects. Our data suggest that the processing of VOT is related to hemispheric dominance for language and that scalp-recorded AEPs may represent an effective, non-invasive method to establish hemispheric dominance for language in clinical settings. This procedure could complement existing methods and could help to detect the dissociation between receptive and expressive language sometimes observed in patients with epilepsy.

Acoustic Stimulation↗
PubMed2004

Scalp hair analysis as a tool in assessing human exposure to heavy metals (S. Domingos mine, Portugal).

Hair samples from the scalp were used in a preliminary assessment of heavy metals exposure (As, Cd, Cr, Cu, Mn and Zn) of the human population living near an abandoned cupric pyrite mine (Mina de S. Domingos, Southeast Alentejo, Portugal). In parallel with the collection of hair samples, individuals from two different communities at the South and North of the mine area answered a questionnaire designed to obtain information about potential exposure pathways to these elements. The questionnaire allowed data collection about the most frequently consumed foodstuffs, drinking water sources, smoking habits, alcohol consumption and health condition. Higher concentrations, and subsequently higher ranges, of Cd, Cu and As were recorded in individuals living near the mine (MSD group), in opposition to individuals living several kilometers apart. Additionally, the concentrations recorded in the hair of some individuals from the MSD group were above the reference values for non-exposed individuals, suggesting their enhanced exposure. However, no significant differences were found for the average concentration of these elements between villages. Individuals from the CP and SC groups presented significantly higher concentrations of Zn and Mn in scalp hair. These results were in agreement with the concentrations of these elements recorded in soil samples. The water supplies of the area do not seem to be potential sources of trace elements for human beings. In opposition, individuals that frequently consume milk and cheese obtained from cattle that usually breeds in the area presented significantly higher concentrations of As and Mn in their scalp hair. Our results suggest that the population of S. Domingos mine area and neighbour localities may be exposed to some of the elements analysed namely Mn and Zn. The most likely exposure pathways seemed to be animal foodstuffs, however, a more detailed analysis of these products, as well as garden vegetables and fruits, should be performed.

Adult↗
PubMed1997

The pathophysiology of giant SEPs in cortical myoclonus: a scalp topography and dipolar source modelling study.

Somatosensory evoked potential (SEP) recordings in patients suffering from cortical myoclonus (CM) are characterised by evidence of abnormally enhanced scalp components. Our aim was to verify whether enhanced activity in giant SEPs arises from the same generators as in healthy subjects. We used the brain electrical source analysis (BESA) to compare scalp SEP generators of healthy subjects to those calculated in 3 patients with CM of varying causes. Firstly, we built a 4-dipole model explaining scalp distribution of early SEPs in normal subjects and then applied it to traces recorded from CM patients. Our model, issued from the right median nerve grand average and applied also to recordings from single individuals, included a dipole at the base of the skull and three other perirolandic dipoles. The first of the latter dipoles was tangentially oriented and was active at the same latencies as the N20/P20 potentials and, with opposite polarity, the P24/ N24 responses; the second dipole explained the central P22 distribution and the third had a peak of activity corresponding to the N30 component. When we applied our 4-dipole model to CM recordings, the first perirolandic dipole had a third peak of activity in all patients at the same latency as a parietal negativity and a frontal positivity, both following giant P24/N24 components; on the other hand, in one patient the second perirolandic dipole showed a later activation corresponding to a high central negativity, following a giant P22 response. We suggest that only the initial giant SEPs correspond to physiological potentials evoked in healthy subjects. The occurrence of late giant SEPs could be explained by hyperpolarization, following the postsynaptic excitatory potentials responsible for the early giant components.

Adult↗
PubMed1998

Irrigation in facial and scalp lacerations: does it alter outcome?

STUDY OBJECTIVE: Animal and human studies suggest that irrigation lowers the infection rate in contaminated wounds, but there is no evidence that this common practice is beneficial for "clean" lacerations. We tested the null hypothesis that there is no difference in the infection rate for noncontaminated lacerations to the face and scalp that are irrigated before primary closure compared with similar wounds that are closed primarily without irrigation. METHODS: We performed a cross-sectional study of consecutive patients presenting to a suburban, academic emergency department between October 1992 and August 1996. Patients with nonbite, noncontaminated facial skin or scalp lacerations who presented less than 6 hours after injury were included. Structured, closed-question data collection instruments were completed at the time of laceration repair and at suture removal. The primary outcome parameters were the incidence of wound infection and the short-term cosmetic appearance of lacerations in patients who did or did not receive irrigation. RESULTS: A total of 1,923 patients were included in the study group; 1,090 patients received saline irrigation, and 833 patients did not. The irrigation and nonirrigation groups were similar with regard to time from injury to presentation (1.56 versus 1.42 hours, respectively), frequency of linear wound morphology (82% versus 88%), frequency of smooth wound margins (72% versus 82%), number of layers of closure (1.14 versus 1.26), number of skin sutures applied (4.98 versus 4.65), number of deep sutures applied (.70 versus 1.05), and use of oral antibiotic prophylaxis (2.8% versus 4.0%). With respect to outcomes, the incidence of wound infection was not significantly different between the two treatment groups (.9% versus 1.4%, respectively; P = .28). Likewise, the percentage of patients who had an "optimal" cosmetic appearance was similar in the two groups (75.9% versus 81.7%, respectively; P = .07). CONCLUSION: Irrigation before primary closure did not significantly alter the rate of infection or the cosmetic appearance in our study population with clean, noncontaminated facial and scalp lacerations.

Adolescent↗
PubMed2003

Magnetoencephalographic yield of interictal spikes in temporal lobe epilepsy. Comparison with scalp EEG recordings.

To compare magnetoencephalography (MEG) with scalp electroencephalography (EEG) in the detection of interictal spikes in temporal lobe epilepsy (TLE), we simultaneously recorded MEG and scalp EEG with a whole-scalp neuromagnetometer in 46 TLE patients. We visually searched interictal spikes on MEG and EEG channels and classified them into three types according to their presentation on MEG alone (M-spikes), EEG alone (E-spikes), or concomitantly on both modalities (M/E-spikes). The M-spikes and M/E-spikes were localized with MEG equivalent current dipole modeling. We analyzed the relative contribution of MEG and EEG in the overall yield of spike detection and also compared M-spikes with M/E-spikes in terms of dipole locations and strengths. During the 30- to 40-min MEG recordings, interictal spikes were obtained in 36 (78.3%) of the 46 patients. Among the 36 patients, most spikes were M/E-spikes (68.3%), some were M-spikes (22.1%), and some were E-spikes (9.7%). In comparison with EEG, MEG gave better spike yield in patients with lateral TLE. Sources of M/E- and M-spikes were situated in the same anatomical regions, whereas the average dipole strength was larger for M/E- than M-spikes. In conclusion, some interictal spikes appeared selectively on either MEG or EEG channels in TLE patients although more spikes were simultaneously identified on both modalities. Thus, simultaneous MEG and EEG recordings help to enhance spike detection. Identification of M-spikes would offer important localization of irritative foci, especially in patients with lateral TLE.

Adolescent↗
PubMed2000

An observation on the mercury contents of scalp hair in the urban residents of South Korea.

The average value of total mercury (THg) in scalp hair of male residents in Seoul city was 1.7+/-0.18 ppm (mean+/-S.E.) and that of methylmercury (MeHg), 1.0+/-0.12 ppm (58.8% THg). In female, level of THg was 1.1+/-0.15 ppm and MeHg was 0.5+/-0.14 ppm (45.5%). Mercury was found more in the scalp hair of male than female (P<0.01). THg/MeHg increased with age of subjects in male (P<0.01), but not female. Coefficients of correlation (r) between THg and MeHg contents in scalp hair of male was +0.877 (P<0.01) and that of female was +0.508 (P<0.01), respectively.

Journal Article↗
PubMed2000

Transient global ischemia specifically modulates visual P300 scalp distribution.

OBJECTIVE: Latency, amplitude, and scalp topography of the visual P300 component was examined in patients who had suffered from transient global ischemia (TGI) due to cardiac arrest and in age matched clinical and healthy controls in order to investigate the diagnostic value of this component. METHOD: Event-related potentials (ERPs) were recorded from 19 scalp electrodes in a visual oddball paradigm. RESULTS: Mean latency of the P300 component was prolonged in both patient groups. Changes in scalp distribution of the P300, however, appear to be specific to anoxic-ischemic encephalopathy. In particular, a selective reduction of the P300 amplitudes at posterior recording sites was observed in TGI patients. Moreover, examination of the auditory P300 in TGI patients revealed that this selective change seems to be restricted to the visual modality. CONCLUSION: The results are discussed with respect to selective vulnerability of brain tissue to hypoxic-ischemic injury. After TGI a modality-specific subset of P300 generators, probably located in the transitional parieto-occipital and extrastriate occipital cortex, appears to be affected. It is also noted, that the visual P300 component could serve as an additional marker of TGI especially in patients who do not show neuropathological changes in structural brain images.

Aged↗
PubMed2001

Scalp topography of ultralate (C-fibres) evoked potentials following thulium YAG laser stimuli to tiny skin surface areas in humans.

AIM: To investigate (1) the scalp topography of ultralate laser evoked potentials (LEPs) related to C-fibre activation, which can directly be obtained by thulium YAG (Tm YAG) laser stimulation of tiny skin surface areas (about 0.23 mm(2)) and (2) the influence of the performance of a motor task on ultralate LEPs. METHODS: Laser stimuli were applied to the dorsum of the left hand. LEPs were recorded with 58 scalp electrodes from 9 healthy subjects in two different conditions, with and without a reaction time (RT) task (press a button upon detection). RESULTS: On high resolution electroenchephalogram recordings, ultralate LEPs were characterized by a broad positive component (peak latency: 1133+/-91 ms) with maximum amplitude about the vertex. Moreover, the performance of a RT task had no influence on latency, amplitude and topographical patterns of two maps chosen at the positive peak latency in ultralate LEPs. Nevertheless, a negative inflexion (latency 1300 ms) appeared after the positive component in the task condition possibly reflecting movement-related potentials. CONCLUSION: Tm YAG laser stimulation of tiny skin surface areas allows recording the dynamic scalp topography of ultralate (C-fibres) LEPs, with or without the performance of a RT task.

Adult↗
PubMed2002

Contribution of GABAergic cortical circuitry in shaping somatosensory evoked scalp responses: specific changes after single-dose administration of tiagabine.

OBJECTIVES: To determine whether conventional as well as high-frequency somatosensory evoked potentials (SEPs) to upper limb stimulation are influenced by GABAergic intracortical circuitry. METHODS: We recorded SEPs from 6 healthy volunteers before and after a single-oral administration of tiagabine. Conventional low-frequency SEPs have been obtained after stimulation of the median nerve, as well as after stimulation of the first phalanx of the thumb, which selectively involves cutaneous finger inputs. Median nerve SEPs have been further analyzed after digital narrow-bandpass filtering, to selectively examine high-frequency responses. Lastly, in order to explain scalp SEP distribution before and after tiagabine administration, we performed the brain electrical source analysis (BESA) of raw data. RESULTS: After tiagabine administration, conventional scalp SEPs showed a significant amplitude increase of parietal P24, frontal N24 and central P22 components. Similarly, BESA showed a significant strength increase of the second peak of activation of the first two perirolandic dipoles, which are likely to correspond to the N24/P24 and P22 generators. By contrast, no significant changes of high-frequency SEPs were induced by drug intake. CONCLUSIONS: Our findings support the view that both N24/P24 and P22 SEP components are probably generated by deep spiny cell hyperpolarization, which is strongly increased by inhibitory inputs from GABAergic interneurons. By considering the clear influence of inhibitory circuitry in shaping these SEP components, conventional scalp SEP recording could be useful in the functional assessment of the somatosensory cortex in different physiological and pathological conditions. By contrast, intrinsic firing properties of the cell population generating high-frequency SEP responses are unaffected by the increase of recurrent GABAergic inhibition.

Adult↗
PubMed1997

Description of the intrafollicular delivery of large molecular weight molecules to follicles of human scalp skin in vitro.

The objective of this study was to ascertain the elements that govern the intrafollicular delivery of large molecules to follicles of human scalp skin in vitro. The experiments were designed to assess the intrafollicular disposition of drug as a function of size, charge, and formulation. First, fluorescein covalently linked to antisense oligonucleotides and rhodamine-conjugated dextrans were topically applied to fresh human scalp skin in vitro. The drug position in the follicle was qualitatively determined by examining histologic sections of hair-bearing skin taken parallel to the skin surface at various depths and dissected hair follicles via fluorescent microscopy. Using radiolabeled antisense oligonucleotides we demonstrated that these cross sections can also be used to quantitatively localize the intrafollicular delivery of large molecules to follicles of human scalp skin in vitro. Experimental results showed that cationic lipid-based formulations enhanced delivery of oligonucleotides within the follicle. The qualitative analysis also illustrated that cationic lipid-based formulations directed the intrafollicular permeation along the junction of the internal and external root sheath. The charged, lower molecular weight (MW) dextrans permeated into all components of the hair follicle, including the hair shaft. The higher MW dextrans were confined to the follicular structures immediately surrounding the hair shaft. The demonstration of quantitation showed that approximately 0.5% of the applied dose was delivered to the hair bulbs and the deeper skin strata within 24 h of a single application. We conclude that topically applied agents of relatively large MW, in properly formulated delivery vehicles; have the potential to reach pharmacologically active concentrations at the hair bulb. It also should be noted that delivery takes place via the junction of the internal and external root sheath.

Dextrans↗
PubMedDate not supplied

Erythema nodosum induced by kerion celsi of the scalp.

A 5-year-old girl presented with a 2-week history of a sharply demarcated, inflammatory, granulomatous lesion on the right side of her scalp. Shortly afterward, painful, subcutaneous nodules developed on her shins and thighs. Trichophyton mentagrophytes was isolated from the scalp lesion and a diagnosis of erythema nodosum induced by kerion of the scalp was made. The patient was started on oral therapy with 18 mg/kg/day griseofulvin, associated with topical crystal violet. Her erythema nodosum regressed in 10 days, while the kerion healed 6 weeks later, leaving residual scarring alopecia. Erythema nodosum represents a reaction pattern to a wide variety of inflammatory stimuli. The interest of this case lies in the unusual association of kerion erythema nodosum, of which only nine cases have been reported in the international literature.

Antifungal Agents↗
PubMed1989

Influence of the fetal scalp electrode stimulation test on fetal heart rate and body movements in quiet and active behavioral states during labor.

Thirty women were studied to examine the effect of fetal scalp stimulation on fetal heart rate (FHR) accelerations and gross body movements in quiet and active fetal behavioral states during the active phase of labor. Stimulation was performed by five consecutive tractions of the fetal scalp electrode. Fetal response in terms of fetal movements and FHR accelerations occurring within 15 seconds after stimulation was observed in all fetuses of the active state group. In the quiet state group 14 of 15 fetuses responded with body movements and in 12 fetuses FHR accelerations were observed. Subsequently, most of the fetuses returned to the quiet state. We suggest that a normal and healthy fetus is expected to respond to the fetal scalp electrode stimulation test even in the quiet behavioral state.

Electrodes↗