Somatosensory evoked potentials in children with brain ventricular dilatation

Aim

To determine possible nerve conduction changes in the somatosensory pathway in children with brain ventricular dilatation and to estimate the relation between the ventricular size and somatosensory evoked potentials (SEP).

Methods

Twelve children with ventricular dilatation (frontal and occipital horn ratios >0.44) and 19 children without ventricular dilatation (control group), aged between 2 and 15 years, were included in the study. Somatosensory evoked responses to median nerve stimulation were recorded in both groups. Evoked potentials were recorded by silver/silver-chloride cup electrodes from Erb’s point in the supraclavicular fossa (wave N9), the cervical spine at the C7 vertebral prominence (wave N13), and the scalp above the contralateral sensory cortex at the point C3’ or C4’, 1 cm behind the C3 or C4 site in the standard 10-20 system (wave N19). Computed tomography scanning was performed to estimate ventricular dilatation.

Results

The conduction time of the central somatosensory pathway (N19-N13 interwave latency) was significantly longer in the children with ventricular dilatation than in the control group (P = 0.046). A statistically significant but weak correlation was found between the frontal and occipital horn ratio values and the N19-N13 interwave latencies in the subjects with enlarged ventricles (r = 0.579, P = 0.045)

Conclusion

Ventricular dilatation is associated with prolonged conduction of the central part of the somatosensory pathway in children. Early detection and treatment of hydrocephalus could be useful in preventing long-term consequences of high intraventricular pressure.Testing of somatosensory evoked potentials (SEP) is a noninvasive, objective method for evaluating the central and peripheral nervous systems, and can also generate information about the maturation of the human afferent sensory system (1,2). This testing is particularly useful in infants and children because the clinical sensory neurological examination in these patients is often difficult and unreliable. In infants with hydrocephalus, both visual and auditory brainstem evoked potentials have already been studied (3,4). However, a limited number of studies have been done to assess SEPs in such infants (5).Hydrocephalus is characterized by diffuse cortical and subcortical damage and therefore differs from other pathologies that result from discrete lesions. Neurophysiological consequences of hydrocephalus and their influence on the function of different neuroanatomic structures are not well known. In children, hydrocephalus compromises normal neurological development and can also cause permanent neurocognitive sequels (6). Therefore, special attention should be paid to the early detection and timely treatment of hydrocephalus.The aim of our study was to determine the possible nerve conduction changes in the somatosensory pathway in children with ventricular dilatation and to estimate the relation between the ventricular size and SEPs latencies.     

Short-term modulation of the ipsilateral primary sensory cortex by nociceptive interference revealed by SEPs

We studied the modulation of the topographic arrangement of the human ipsilateral primary somatosensory cortex following interference of nociceptive stimuli by means of dipole source analysis. Multichannel somatosensory evoked potentials were obtained by electrical stimulation of digits 1 and 5 of the left hand before, during and after the application of pain to digits 2-4 of the right hand. The primary cortical response of the SEP (N20) was obtained for dipole localization of the representation of the primary sensory cortex receiving input from digits 1 to 5. The 3D-distance between these sides was calculated for further analysis. To account for possible attentional effects recordings were performed while simultaneously to this intervention subjects were asked to turn their attention to the right or left hand in a pseudorandom order. The application of pain induced an expansion of the 3D-distance between digits 1 and 5. Focusing attention to the stimulated limb or the site of the intervention did not yield to an additional effect. Our results provide further evidence for the presence of a quickly adapting interaction between primary somatosensory areas of both hemispheres following an interference of nociceptive stimulation in SEPs. This modifying process is probably mediated by interhemispheric and intercortical connections leading to hyperexcitability of the primary sensory cortex contralateral to that receiving nociceptive input. Spatial attention does not seem to have an impact on this kind of short-term intercortical plasticity.     

Deviation of somatosensory evoked potential and lateral dominance of spike activity in iron-induced epileptic cortex of the rat

A chronic epileptic focus was induced by a microinjection of ferric chloride solution into the sensorimotor cortex of rats. Two types of somatosensory evoked potentials (SEPs) were recorded from the cortex near the injection site. In animals showing an initial positive-negative biphasic SEP, spikes appeared in electrocorticograms (ECoGs) more frequently on the side ipsilateral to the injection site than on the contralateral side, whereas in animals showing an initial negative monophasic SEP, spikes appeared more frequently on the contralateral side.     

Adaptive changes in early and late blind: a fMRI study of Braille reading.

Braille reading depends on remarkable adaptations that connect the somatosensory system to language. We hypothesized that the pattern of cortical activations in blind individuals reading Braille would reflect these adaptations. Activations in visual (occipital-temporal), frontal-language, and somatosensory cortex in blind individuals reading Braille were examined for evidence of differences relative to previously reported studies of sighted subjects reading print or receiving tactile stimulation. Nine congenitally blind and seven late-onset blind subjects were studied with fMRI as they covertly performed verb generation in response to reading Braille embossed nouns. The control task was reading the nonlexical Braille string "######". This study emphasized image analysis in individual subjects rather than pooled data. Group differences were examined by comparing magnitudes and spatial extent of activated regions first determined to be significant using the general linear model. The major adaptive change was robust activation of visual cortex despite the complete absence of vision in all subjects. This included foci in peri-calcarine, lingual, cuneus and fusiform cortex, and in the lateral and superior occipital gyri encompassing primary (V1), secondary (V2), and higher tier (VP, V4v, LO and possibly V3A) visual areas previously identified in sighted subjects. Subjects who never had vision differed from late blind subjects in showing even greater activity in occipital-temporal cortex, provisionally corresponding to V5/MT and V8. In addition, the early blind had stronger activation of occipital cortex located contralateral to the hand used for reading Braille. Responses in frontal and parietal cortex were nearly identical in both subject groups. There was no evidence of modifications in frontal cortex language areas (inferior frontal gyrus and dorsolateral prefrontal cortex). Surprisingly, there was also no evidence of an adaptive expansion of the somatosensory or primary motor cortex dedicated to the Braille reading finger(s). Lack of evidence for an expected enlargement of the somatosensory representation may have resulted from balanced tactile stimulation and gross motor demands during Braille reading of nouns and the control fields. Extensive engagement of visual cortex without vision is discussed in reference to the special demands of Braille reading. It is argued that these responses may represent critical language processing mechanisms normally present in visual cortex.     

Finger movement is associated with attenuated cutaneous reflexes recorded from human first dorsal interosseous muscle

Cutaneomuscular reflexes (CMR) have been recorded from the first dorsal interosseous muscle (1DI) of the preferred hand, somatosensory evoked potentials (SEP) were recorded from the contralateral sensory cortex and the sensory nerve action potential (SNAP) was recorded from the median nerve of 15 adult subjects whilst electrically stimulating the digital nerves of the index finger. Subjects performed the following tasks (a) a sustained abduction of the index finger against resistance at 10–20 % maximum voluntary contraction (MVC), and (b) abduction of the index finger as in (a) whilst performing self paced low amplitude tapping of the (i) index finger, (ii) thumb, (iii) middle finger, (iv) little finger and (v) ipsilateral foot. The E2 component of the CMR and the N20/P25 components of the SEP were significantly reduced during finger tapping ( P < 0.05). This reduction was independent of which finger was tapping ( P > 0.05). There was a significant (qualitative) relationship between the decrease in the size of the E2 component of the CMR and the N20/P25 components of the SEP (χ² test; P < 0.05). There were no significant changes in E1 and I1 ( P > 0.05). The size of the SNAP was independent of task ( P > 0.05). The size of the E1, I1, E2 components of the CMR, and the N20/P25 components of the SEP were unaltered during foot tapping ( P > 0.05, n = 4). We conclude that the decrease in size of the E2 component associated with finger tapping results from gating of the digital nerve input.     

Human cortical potentials evoked by stimulation of the median nerve. II. Cytoarchitectonic areas generating long-latency activity

1. The anatomic generators of human median nerve somatosensory evoked potentials (SEPs) in the 40 to 250-ms latency range were investigated in 54 patients by means of cortical-surface and transcortical recordings obtained during neurosurgery. 2. Contralateral stimulation evoked three groups of SEPs recorded from the hand representation area of sensorimotor cortex: P45-N80-P180, recorded anterior to the central sulcus (CS) and maximal on the precentral gyrus; N45-P80-N180, recorded posterior to the CS and maximal on the postcentral gyrus; and P50-N90-P190, recorded near and on either side of the CS. 3. P45-N80-P180 inverted in polarity to N45-P80-N180 across the CS but was similar in polarity from the cortical surface and white matter in transcortical recordings. These spatial distributions were similar to those of the short-latency P20-N30 and N20-P30 potentials described in the preceding paper, suggesting that these long-latency potentials are generated in area 3b of somatosensory cortex. 4. P50-N90-P190 was largest over the anterior one-half of somatosensory cortex and did not show polarity inversion across the CS. This spatial distribution was similar to that of the short-latency P25-N35 potentials described in the preceding paper and, together with our and Goldring et al. 1970; Stohr and Goldring 1969 transcortical recordings, suggest that these long-latency potentials are generated in area 1 of somatosensory cortex. 5. SEPs of apparently local origin were recorded from several regions of sensorimotor cortex to stimulation of the ipsilateral median nerve. Surface and transcortical recordings suggest that the ipsilateral potentials are generated not in area 3b, but rather in other regions of sensorimotor cortex perhaps including areas 4, 1, 2, and 7. This spatial distribution suggests that the ipsilateral potentials are generated by transcallosal input from the contralateral hemisphere. 6. Recordings from the periSylvian region were characterized by P100 and N100, recorded above and below the Sylvian sulcus (SS) respectively. This distribution suggests a tangential generator located in the upper wall of the SS in the second somatosensory area (SII). In addition, N125 and P200, recorded near and on either side of the SS, suggest a radial generator in a portion of SII located in surface cortex above the SS. 7. In comparison with the short-latency SEPs described in the preceding paper, the long-latency potentials were more variable and were more affected by intraoperative conditions.     

Human cortical potentials evoked by stimulation of the median nerve. II. Cytoarchitectonic areas generating short-latency activity

1. The anatomic generators of human median nerve somatosensory evoked potentials (SEPs) in the 40 to 250-ms latency range were investigated in 54 patients by means of cortical-surface and transcortical recordings obtained during neurosurgery. 2. Contralateral stimulation evoked three groups of SEPs recorded from the hand representation area of sensorimotor cortex: P45-N80-P180, recorded anterior to the central sulcus (CS) and maximal on the precentral gyrus; N45-P80-N180, recorded posterior to the CS and maximal on the postcentral gyrus; and P50-N90-P190, recorded near and on either side of the CS. 3. P45-N80-P180 inverted in polarity to N45-P80-N180 across the CS but was similar in polarity from the cortical surface and white matter in transcortical recordings. These spatial distributions were similar to those of the short-latency P20-N30 and N20-P30 potentials described in the preceding paper, suggesting that these long-latency potentials are generated in area 3b of somatosensory cortex. 4. P50-N90-P190 was largest over the anterior one-half of somatosensory cortex and did not show polarity inversion across the CS. This spatial distribution was similar to that of the short-latency P25-N35 potentials described in the preceding paper and, together with our and Goldring et al. 1970; Stohr and Goldring 1969 transcortical recordings, suggest that these long-latency potentials are generated in area 1 of somatosensory cortex. 5. SEPs of apparently local origin were recorded from several regions of sensorimotor cortex to stimulation of the ipsilateral median nerve. Surface and transcortical recordings suggest that the ipsilateral potentials are generated not in area 3b, but rather in other regions of sensorimotor cortex perhaps including areas 4, 1, 2, and 7. This spatial distribution suggests that the ipsilateral potentials are generated by transcallosal input from the contralateral hemisphere. 6. Recordings from the periSylvian region were characterized by P100 and N100, recorded above and below the Sylvian sulcus (SS) respectively. This distribution suggests a tangential generator located in the upper wall of the SS in the second somatosensory area (SII). In addition, N125 and P200, recorded near and on either side of the SS, suggest a radial generator in a portion of SII located in surface cortex above the SS. 7. In comparison with the short-latency SEPs described in the preceding paper, the long-latency potentials were more variable and were more affected by intraoperative conditions.(ABSTRACT TRUNCATED AT 400 WORDS)     

78例儿童孤独症患者体感诱发电位分析

目的:通过观察和分析儿童孤独症患者体感诱发电位(SEP)的改变,探讨其在儿童孤独症诊断中的临床意义。方法:对1岁零8个月至8岁的78例孤独症儿童进行SEP检查,观察皮层第一个电位P40潜伏期及P40、N50、P60、N75波幅的改变。结果:78例孤独症患儿皮层电位P40潜伏期均有延长,其中双侧延长55例,单侧延长23例,并波幅分化差或左右不对称18例。结论:孤独症患者体感传导通路皮层电位潜伏期延长和波幅的改变,提示皮层下(包括脑干、丘脑)和相关皮层功能受损的可能,结合影像学检查,对评价神经系统功能及预后有一定的价值,对孤独症患儿临床诊断有帮助。     

Thalamic and cortical high-frequency (600 Hz) somatosensory-evoked potential (SEP) components are modulated by slight arousal changes in awake subjects

Human somatosensory-evoked potentials (SEP) recorded at the scalp after conventional electrical median-nerve stimulation contain a low-amplitude (<500 nV), high-frequency (approximately 600 Hz) burst of repetitive wavelets, which are superimposed onto the primary cortical response N20. Previous electroencephalographic (EEG) studies have shown: (1) that these wavelets are generated near the hand area of the primary somatosensory cortex and in deep fibers of thalamocortical afferences; and (2) that only the 600-Hz burst, but not the N20 is decreased during sleep. Since the thalamus is involved in regulating both, selective attention and arousal, the present study aimed at characterizing the effects of focused attention and slight arousal changes on the 600-Hz oscillations. A dipole-source analysis of 64-channel SEP recordings after electric right-median-nerve stimulation allowed the comparison of brainstem, thalamic, and two cortical (one tangential, one radial) source activities in ten awake human subjects under two slightly different arousal states (eyes open vs. eyes closed), each tested for three conditions of focused attention (directed towards rare acoustic and right- or left-hand somatosensory target stimuli). While the N20 was not modified at all, the source strength of the high-frequency wavelet burst was significantly increased for eyes opened versus eyes closed, at the thalamic source site as well as for the tangentially oriented cortical source. In contrast, there were no significant differences between conditions with different attentional targets. This evidence for modulatory effects of increased arousal (eyes open) on both thalamic and cortically generated high-frequency SEP activity fits the hypothesis that the 600-Hz SEP burst at least partially represents an arousal-dependent signal generated at the thalamic level and transmitted to the primary somatosensory cortex.     

Source Dipole Analysis of the Early Components of the RREP

Occlusion of the inspiratory airway produces a series of early RREP components. The predominant early positive and negative peaks are seen over the parietal and frontal scalp respectively and have been hypothesised to represent parallel activation of somatosensory and motor cortices in a manner similar to electrically produced SEP components. An alternative hypothesis is that both components are produced by somatosensory cortex, with the frontally maximal negativity reflecting the activity of a tangential dipole source. Respiratory-related evoked potentials (RREPs) elicited by brief occlusion of the inspiratory airway, were recorded using 29 scalp electrodes from six subjects. Early latency components were analysed using the Electromagnetic Source Estimation (EMSE) program for modelling equivalent electrical dipoles, in order to suggest likely generator sources. Two hypotheses were tested: first, that radial dipoles generated by both pre- (motor cortex) and post-centrally (somatosensory cortex) produce the early components; and second, that generator sources are limited to the somatosensory cortex, with activity recorded as frontally maximal reflecting volume conduction from tangential dipoles. Results were highly consistent between subjects and suggested that Nf-P1 was best accounted for by two post-central and two pre-central radial dipoles supporting the first hypothesis. Locations of generator sources are discussed in relation to anatomical correlates.     

The cholinergic innervation develops early and rapidly in the rat cerebral cortex: a quantitative immunocytochemical study.

A recently developed method for determining the length of cholinergic axons and number of cholinergic axon varicosities (terminals) in brain sections immunostained for choline acetyltransferase was used to estimate the areal and laminar densities of the cholinergic innervation in rat frontal (motor), parietal (somatosensory) and occipital (visual) cortex at different postnatal ages. This cortical innervation showed an early beginning, a few immunostained fibers being already present in the cortical subplate at birth. In the first two postnatal weeks, it developed rapidly along three parameters: a progressive increase in the number of varicosities per unit length of axon, and a lengthening and branching of the axons. Between postnatal days 4 and 16, the number of varicosities increased steadily from two to four per 10 microm of cholinergic axon. The mean densities of cholinergic axons increased from 1.4 to 9.6, 1.7 to 9.3 and 0.7 to 7.2 m/mm(3), and the corresponding densities of varicosities from 0.4 to 3.9, 0.4 to 3.5, and 0.2 to 2.6x10(6)/mm(3) in the frontal, parietal and occipital areas, respectively. The rate of growth was maximal during these first two weeks, after which the laminar pattern characteristic of each area appeared to be established. Adult values were almost reached by postnatal day 16 in the parietal cortex, but maturation proceeded further in the frontal and particularly in the occipital cortex.These quantitative data on the ingrowth and maturation of the cholinergic innervation in postnatal rat cerebral cortex substantiate a role for acetylcholine in the development of this brain region and emphasize the striking growth capacity of individual cholinergic neurons.     

Quantitative changes in fibro-architectonics of the human cerebral cortex from birth to 12 years of age

The peculiarities of fibroarchitectonics in topographically and functionally distinct cortical zones (including temporo-parieto-occipital subarea, occipital, pre-, postcentral, and frontal areas) were studied in the brain specimens of 74 children of different ages (from birth to 12 years) taken with yearly intervals, while those in the first year of life--with monthly intervals. Frontal sections stained with Nissl, Peters and Golgi methods were studied using computer analysis of optical images. The data were obtained on the increment rates of radial fiber fascicles' thickness, distances between fascicles and age dynamics of ratios of volume densities of neurons and fibers in areas 3, 4p, 6op, 17, 19, 37ac, 44 and 32/10. It was shown that age-related transformations of fibroarchitectonics in the areas of sensomotor, somatosensory, occipital, temporo-parieto-occipital and frontal cortex were heterochronic and took place with different intensity; most pronounced changes were found to occur during the first 2-3 years, while less intensive ones were observed up to the age of 9-12 years.     

Control of cerebral cortical blood flow by stimulation of basal forebrain cholinergic areas in mice

We examined whether activity of the nucleus basalis of Meynert (NBM) regulates regional cerebral cortical blood flow (rCBF) in mice, using laser speckle and laser Doppler flowmetry. In anesthetized mice, unilateral focal stimulation, either electrical or chemical, of the NBM increased rCBF of the ipsilateral cerebral cortex in the frontal, parietal and occipital lobes, independent of changes in systemic blood pressure. Most of vasodilative responses to low intensity stimuli (2 times threshold intensity: 2T) were abolished by atropine (a muscarinic cholinergic blocker), whereas responses to higher intensity stimuli (3T) were abolished by atropine and mecamylamine (a nicotinic cholinergic blocker). Blood flow changes were largest when the tip of the electrode was located within the area containing cholinergic neurons shown by choline acetyltransferase-immunocytochemistry. These results suggest that cholinergic projections from basal forebrain neurons in mice cause vasodilation in the ipsilateral cerebral cortex by a combination of muscarinic and nicotinic mechanisms, as previously found in rats and cats.     

A comparison of awake and sleeping cortical states by analysis of the somatosensory-evoked response of postcentral area 1 in rhesus monkey

Summary The response of primary somatosensory cortex (SI) to cutaneous stimulation of the hand was studied in one unanesthetized monkey to examine more closely the previously reported dependence of a behaviorally relevant late component of the evoked potential, N1, upon two behavioral states of arousal, slow-wave sleep (SWS) and inactive wakefulness. Simultaneous recordings of the somatosensory-evoked potentials (SEP), multiple unit activities (MUA) and current source-densities (CSD) at 12 depths through area 1 were collected during both states and analyzed to identify the cortical events that generate the SEP. As previously reported, the N1 component of the SEP was diminished during sleep. Although the earlier components of the SEP were evoked during both states, the excitatory events that characterize the awake N1 were replaced during SWS by an interval of strong inhibition which was terminated by a burst of cortical MUA. CSD analysis of the SWS inhibitory interval revealed large current sources through layer III above the depth of maximal MUA inhibition indicating that an outward conductance became activated on the apical trunks of pyramidal neurons during SWS. These data support the proposed involvement of events underlying N1 in the coding of touch experience.     

Transient increase in glutamic acid decarboxylase mRNA in the cerebral cortex following focal cortical lesion in the rat

Summary In situ hybridization histochemistry (ISHH) was used to study the expression of glutamic acid decarboxylase (GAD) mRNA changes in the rat cerebral cortex following unilateral frontal and somatosensory cortical lesion by devascularisation. 4 days after the lesion, a significant transient increase in GAD mRNA level in the ipsilateral cortex was observed when compared with contralateral, ipsi-sham operated and ipsi-normal control cortices. The change occurred throughout the ipsilateral neocortex, with no significant difference between the magnitude of increase in frontal, parieto-occipital, parieto-temporal, cingulate or retrosplenial areas; no obvious change was seen in pyriform, entorhinal or hippocampal cortices. This unexpected GAD mRNA increase in neocortex may be part of a long term adaptive functional alteration and changes in the gene expression of the cerebral cortex following focal cortical injury.A preliminary report of these findings was presented at the annual general meeting of the Anatomical Society of Great Britain and Ireland     

Muscarinic cholinergic receptor subtypes in cerebral cortex of Fisher 344 rats: a light microscope autoradiography study of age-related changes

The density and localization of muscarinic cholinergic M1-M5 receptor subtypes was investigated in frontal and occipital cortex of male Fisher 344 rats aged 6 months (young-adult), 15 months (mature) and 22 months (senescent) by combined kinetic and equilibrium binding and light microscope autoradiography. In 6-month-old rats, the rank order density of muscarinic cholinergic receptor subtypes was M1>M2>M4>M3>M5 both in frontal and occipital cortex. A not homogeneous distribution of different receptor subtypes throughout cerebrocortical layers of frontal or occipital cortex was found. In frontal cortex silver grains corresponding to the M1 and M2 receptor subtypes were decreased in 15- and 22-month-old groups. The M3 receptor density was remarkably and moderately decreased in layers II/III and V, respectively, of rats aged 15 and 22 months. A reduced M4 receptor density was observed in layer I and to a lesser extent in layer V of mature and senescent rats, whereas no age-related changes of M5 receptor were found. In occipital cortex a diminution of M1 receptor was observed in layers II/III and V of mature and senescent rats. The M2 receptor expression decreased in layer I of 15- and 22-month-old senescent rats, whereas M3-M5 receptors were unchanged with exception of a slight decrease of the M4 receptor in layer IV and of M5 receptor in layers II/III. These findings indicate a different sensitivity to aging of muscarinic receptor subtypes located in various cerebrocortical layers. This may account for the difficulty in obtaining relevant results in manipulating cholinoceptors to counter age-related impairment of cholinergic system.     

Quantitative Changes in the Fibroarchitectonics of the Human Cortex from Birth to the Age of 12 Years

Brains from 74 children aged from birth to 12 years were used to study fibroarchitectonic characteristics in topographically and functional diverse cortical zones (the temporal-parietal-occipital subregion, occipital, precentral, postcentral, and frontal areas) of the cerebral cortex; children aged up to 12 months were studied on the basis of one-month age intervals. Studies were performed by computer analysis of optical images on frontal sections stained with Nissl cresyl violet and silver nitrate impregnation by the modified Peters method. Data on the rate of increase in the thickness of radial bundles of fibers, the distances between bundles, and the age dynamics of the ratios of the specific volumes of neurons and fibers in fields 3, 4p, 6op, 17, 19, 37ac, 44, and 32/10 were obtained. These measurements showed that age-related transformation of fibroarchitectonics in fields of the sensorimotor, somatosensory, occipital, temporal-parietal-occipital, and frontal areas occurred at different times and with different intensities; the most significant changes were seen in the first 2-3 years of life, with changes continuing at a less intense level to age 9-12 years.     

Preferential ipsilateral influence of the posterior hypothalamus on the neocortex

On the 10th-20th day after precollicular transection of the brain stem weak low-frequency electrical stimulation of the posterior hypothalamus preferentially activates the ipsilateral neocortex. After unilateral injury to the posterior hypothalamus, synchronous activity predominates in the ipsilateral neocortex. In premesencephalic animals weak single electrical stimulation of the posterior hypothalamus evokes the appearance of spindles in ipsilateral zones of the frontal cortex, whereas stronger single stimulation causes the diffuse generation of spindles in various parts of the neocortex. Besides this preferential unilateral effect, the influence of the posterior hypothalamus is found to be more strongly expressed in the frontal than in the occipital cortex. It is postulated that the posterior hypothalamus exerts its influence on the neocortex through the thalamic nuclei.Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 139–145, March–April, 1976.     

Spatiotemporal Dynamics of the Cortical Responses Induced by a Prolonged Tactile Stimulation of the Human Fingertips

The sense of touch is fundamental for daily behavior. The aim of this work is to understand the neural network responsible for touch processing during a prolonged tactile stimulation, delivered by means of a mechatronic platform by passively sliding a ridged surface under the subject’s fingertip while recording the electroencephalogram (EEG). We then analyzed: (i) the temporal features of the Somatosensory Evoked Potentials and their topographical distribution bilaterally across the cortex; (ii) the associated temporal modulation of the EEG frequency bands. Long-latency SEP were identified with the following physiological sequence P100—N140—P240. P100 and N140 were bilateral potentials with higher amplitude in the contralateral hemisphere and with delayed latency in the ipsilateral side. Moreover, we found a late potential elicited around 200 ms after the stimulation was stopped, which likely encoded the end of tactile input. The analysis of cortical oscillations indicated an initial increase in the power of theta band (4–7 Hz) for 500 ms after the stimulus onset followed a decrease in the power of the alpha band (8–15 Hz) that lasted for the remainder of stimulation. This decrease was prominent in the somatosensory cortex and equally distributed in both contralateral and ipsilateral hemispheres. This study shows that prolonged stimulation of the human fingertip engages the cortex in widespread bilateral processing of tactile information, with different modulations of the theta and alpha bands across time.     

Change in somatosensory evoked potential in the rat recorded at the hemisphere with iron-induced epileptic focus

In rats, microinjection of FeCl3 solution into the left sensorimotor cortex was performed to induce a chronic epileptic focus. One month or more after the microinjection, electrocutaneous stimuli were applied to part of the wrist joint and 50 consecutive somatosensory evoked potentials (SEPs) were averaged. SEP from the left cortex showed only an initial negative monophasic deflection while SEP from the contralateral cortex showed a normal configuration with initial positive-negative biphasic deflection in the majority of experimental animals.