Somatosensory evoked potentials following lesions of the claustrum

Ipsi- and contralateral cortical somatosensory evoked potentials (SEP) were recorded following median nerve stimulation in 12 patients with unilateral brain lesions and in 5 healthy subjects. Computed tomographic scans of brain were performed on admission. In all patients with lesions of the claustrum there was absence of SEP contralateral to the side of the lesion and ipsilateral to the stimulated nerve. This phenomenon did not appear in our material following lesions involving other structures e.g. thalamus or somatosensory cortex. Our observations suggest that the claustrum may influence deeply the contralateral somatosensory cortex. This may be due to the fact that a large part of the claustrum is involved in transmission of the sensory information from receptors to the somatosensory cortex.     

Effects of Q-switched Nd:YAG laser irradiation on neural impulse propagation: II. Dorsal roots and peripheral nerves.

We have studied the effects of Q-switched Nd:YAG laser irradiation on transmission of neural impulses in sensory nerve fibers in anesthetized rats and cats. Laser light was applied to dorsal roots (rat, cat) and to the sciatic nerve (rat) at increasing pulse energies ranging from 10 to 100 mJ/pulse for 5 minutes each. Compound action potentials recorded from dorsal roots and the sciatic nerve in response to high intensity electrical stimulation during laser application at increasing pulse energies showed a progressive preferential reduction of the slow late component of the electrically evoked response. Preliminary data from multifilament recordings from dorsal roots in cats demonstrated that conduction in small slow conducting fibers was blocked at lower laser pulse energies than in fibers with faster conduction velocities. These results imply, that laser light might have differential effects on slow versus fast conducting sensory nerve fibers. It is most likely that the preferential effect of laser irradiation on slow conducting fibers is mediated by photothermal mechanisms, since temperature increased substantially during laser application.     

Topography of middle-latency somatosensory evoked potentials following painful laser stimuli and non-painful electrical stimuli

The aim of this study was to compare cerebral evoked potentials following selective activation of Aβ and Aδ fibers. In 15 healthy subjects, Aβ fibers were activated by electrical stimulation of the left radial nerve at the wrist. Aδ fibers were activated by short painful radian heat pulses, applied to the dorsum of the left hand by a CO₂ laser. Evoked potentials were recorded with 15–27 scalp electrodes, evenly distributed over both hemispheres (bandpass 0.5–200 Hz). The laser-evoked potentials exhibited a component with a mean peak latency of 176 msec (N170). Its scalp topography showed a parieto-temporal maximum contralateral to the stimulus side. In contrast, the subsequent vertex negativity (N240), which appeared about 60 msec later, had a symmetrical scalp distribution. Electrically evoked potentials showed a component at 110 msec (N110), that had a topography similar to the laser-evoked N170. The topographies of the N170 and N110 suggest that they may both be generated in the secondary somatosensory cortex. There was no component in the electrically evoked potential that had a comparable interpeak latency to the following vertex potential: for N60 it was longer, for N110 it was shorter. On the other hand, in the laser-evoked potentials no component could be identified the topography of which corresponded to the primary cortical component N20 following electrical stimulation.     

Determination of conduction times of the peripheral and central parts of the sensory pathway using evoked somatosensory potentials

Determination of conduction times of the peripheral and central parts of the sensory pathway using evoked somatosensory potentials. Acta physiol. pol., 1985, 36 (3): 216-223. Simultaneous recording of the somatosensory evoked potentials (SEP) from Erb's point, neck and scalp allows investigation of the peripheral and central conduction times. The early components of the SEP produced by stimulation of the median nerve at the wrist were recorded using standardized electrode locations in 15 normal subjects. The difference of the latencies between the first peak of the cortical response (N20) and the peak of the neck response (N14) reflects, probably, the conduction time between the dorsal column nuclei and the cortex. Its value was 6 +/- 0.7 msec. The conduction time difference (between peak Erb's point response (N9) and N14) was 5.5 +/- 0.5 msec and it reflected the peripheral conduction time. For diagnostic application the lower limit of the response amplitudes was determined also for every component.     

外周诱发电位的模型研究

本文根据容积导体中有关动作电位的电生理理论,用三点源模型模拟单根纤维动作电位(SFAP),并假设神经束的复合动作电位(CAP)是由SFAP线性叠加而成,给出了神经束CAP的模型.通过运用上述模型,计算了正常人正中神经纤维传导速度分布,分析了刺激腕部正中神经引导的传感诱发电位(SEP)的N~-_9成分;另外,还得出一些描述此外周传导通路性质的其它参数,如平均传导速度、神经纤维活动最可几传速度分布范围等.此方法可用来研究其它各种外围诱发电位.     

Neurological dysfunction in asymptomatic HIV-1 infected men: evidence from evoked potentials

Neurological function in 159 subjects infected by the human immunodeficiency virus (HIV) who had no neurological symptoms or signs (129 asymptomatic, 30 with ARC/AIDS) was compared to that of 62 controls by means of pattern-reversal evoked potentials (PREPs), brain-stem auditory evoked potentials (BAEPs), median nerve somatosensory evoked potentials (MSEPs), tibial nerve somatosensory evoked potentials (TSEPs) and nerve conduction studies (NCSs). Central nervous system somatosensory conduction from lumbar cord to cortex was prolonged in both asymptomatic seropositive and ARC/AIDS groups, while peripheral somatosensory conduction, NCSs and PREP delays occurred only in the ARC/AIDS group. BAEPs did not show significant differences among groups. TSEPs were abnormal in 8% of asymptomatic carriers and 43% of patients with ARC/AIDS, MSEPs in 7% and 20%, PREPs in 4% and 0%, and BAEPs in 1% and 0% respectively. One or more evoked potentials were abnormal in 18 of 129 (14%) asymptomatic carriers and 13 of 30 (43%) subjects with ARC/AIDS as compared with 1 of 62 (2%) seronegative controls. We conclude that asymptomatic HIV carriers have subclinical neurological impairment of central somatosensory function and that the neurological impairment increases with disease progression to involve peripheral nerves and visual system.     

Interhemispheric interactions between the human primary somatosensory cortices

In the somatosensory domain it is still unclear at which processing stage information reaches the opposite hemispheres. Due to dense transcallosal connections, the secondary somatosensory cortex (S2) has been proposed to be the key candidate for interhemispheric information transfer. However, recent animal studies showed that the primary somatosensory cortex (S1) might as well account for interhemispheric information transfer. Using paired median nerve somatosensory evoked potential recordings in humans we tested the hypothesis that interhemispheric inhibitory interactions in the somatosensory system occur already in an early cortical processing stage such as S1. Conditioning right S1 by electrical median nerve (MN) stimulation of the left MN (CS) resulted in a significant reduction of the N20 response in the target (left) S1 relative to a test stimulus (TS) to the right MN alone when the interstimulus interval between CS and TS was between 20 and 25 ms. No such changes were observed for later cortical components such as the N20/P25, N30, P40 and N60 amplitude. Additionally, the subcortically generated P14 response in left S1 was also not affected. These results document the existence of interhemispheric inhibitory interactions between S1 in human subjects in the critical time interval of 20-25 ms after median nerve stimulation.     

Activation of thalamic ventroposteriolateral neurons by phrenic nerve afferents in cats and rats.

It has been demonstrated that phrenic nerve afferents project to somatosensory cortex, yet the sensory pathways are still poorly understood. This study investigated the neural responses in the thalamic ventroposteriolateral (VPL) nucleus after phrenic afferent stimulation in cats and rats. Activation of VPL neurons was observed after electrical stimulation of the contralateral phrenic nerve. Direct mechanical stimulation of the diaphragm also elicited increased activity in the same VPL neurons that were activated by electrical stimulation of the phrenic nerve. Some VPL neurons responded to both phrenic afferent stimulation and shoulder probing. In rats, VPL neurons activated by inspiratory occlusion also responded to stimulation on phrenic afferents. These results demonstrate that phrenic afferents can reach the VPL thalamus under physiological conditions and support the hypothesis that the thalamic VPL nucleus functions as a relay for the conduction of proprioceptive information from the diaphragm to the contralateral somatosensory cortex.     

Nerve,spinal cord and brain somatosensory evoked responses: a comparative study during electrical and magnetic peripheral nerve stimulation

Somatosensory evoked potentials (SEPs) and compound nerve action potentials (cNAPs) have been recorded in 15 subjects during electrical and magnetic nerve stimulation. Peripheral records were gathered at Erb's point and on nerve trunks at the elbow during median and ulnar nerve stimulation at the wrist. Erb responses to electrical stimulation were larger in amplitude and shorter in duration than the magnetic ones when ‘electrical’ and ‘magnetic’ compound muscle action potentials (cMAPs) of comparable amplitudes were elicited. SEPs were recorded respectively at Cv7 and on the somatosensory scalp areas contra- and ipsilateral to the stimulated side. SEPs showed a statistically significant difference in amplitude only for the brachial plexus response and for the ‘cortical’ N20-P25 complex; differences were not found between the magnetic and electrical central conduction times (CCTs) or for the peripheral nerve response latencies. Magnetic stimulation preferentially excited the motor and proprioceptive fibres when the nerve trunks were stimulated at motor threshold intensities.     

Evoked potentials in the rat neostriatum during local cooling of the cortex in the zone of primary response to the applied stimulus

The effect of local cooling of the surface of the somatosensory cortex was studied while recording primary response (PR) in the center of a cooled area and evoked potentials (EP) in the striatum to the forepaw stimulation. The cooling which served to arise the amplitude of the PR, served also to arise the amplitude of the EP in the striatum. EP to the stimulus, the sensory representation of which in the cortex was cooled, were facilitated only. Facilitation of the striatal EP was more intense than facilitation of the cortical PR in the cooled area. The level of facilitation of the EP was the same in the region of the striatum which receives corticofugal fibers from the cooled area of the cortex and in other regions of the striatum, receiving the corticofugal fibers from other parts of the cortex. The data show a possibility for the interactions in the striatum of the corticofugal signals from different cortical areas with each other and with the ascending afferent signals.     

Human cerebrocortical potentials evoked by stimulation of the dorsal nerve of the penis

Cortical evoked potentials resulting from stimulation of the dorsal nerve of the penis (DNP) provide a unique opportunity to document the cortical localization of sexual sensory representation in man. The DNP supplies sensory axons to the major portion of the human phallus, including the penile shaft and glans. Animal and human studies indicate that this nerve plays a crucial role in erection and ejaculation. Direct cortical evoked responses to DNP electrical stimulation were recorded in patients undergoing preoperative evaluation for resection of epileptic foci. These studies provided evidence that the primary sensory cortex contains a large area of cortex devoted to the afferent fibers of the DNP and that the sensory field is in a different location than previously described. The location and distribution of this response indicated the need for revision of the traditional concept of the sensory cortical homunculus.     

Functional deficits of central sensory and motor pathways in patients with cervical spinal stenosis: a study of SEPs and EMG responses to non-invasive brain stimulation

The central conduction time of the descending and ascending fibers of the spinal cord were examined in patients with radiologically defined cervical spinal stenosis (antero-posterior diameter of the spinal canal less than 13 mm). Nineteen patients were examined, only 4 of whom showed clinical signs of spastic weakness or ataxia. The electromyographic response after non-invasive stimulation of the leg area of the motor cortex was delayed in13 of the 15 clinically unaffected patients. The central latency (N21-P39) of the somatosensory evoked response after stimulation of the tibial nerve (tibialis SEP) was increased in 12 of the 15 individuals. The 4 patients with clinical signs showed abnormal latencies with both methods.The use of both techniques for the examination of the function of the spinal cord revealed increased latencies in the central motor and/or sensory pathways in all patients. The technique of non-invasive stimulation of the corticospinal system therefore provides an additional tool to detect and quantity subclinical and clinically apparent lesions in patients with defined cervical spinal stenosis.     

Release of segmental amino acid neurotransmitters in response to peripheral afferent and motor cortex stimulation: A pilot study

The role of amino acid (AA) neurotransmitters in the spinal cord has been primarily studied using in vitro preparations and histochemical methods. The technology necessary to estimate AA levels in an intact animal has only recently become available. Such an investigation could yield valuable information regarding the segmental neurochemical environment. We measured the release of AAs into the rabbit lumbar spinal cord in response to sciatic nerve and transcranial stimulation with stereotaxically placed microdialysis catheters. Samples were obtained periodically during 90 minutes of continuous stimulation of either the left or right sciatic nerve, or motor cortex. Quantification of γ-amino butyric acid (GABA), aspartate, glutamate, glycine, and taurine was performed using high pressure liquid chromatography (HPLC). Adequate neural excitation was verified by recording somatosensory evoked potentials (SSEPs) or corticomotor evoked potentials (CMEPs). Sensory activation at intensities sufficient to activate small and large diameter peripheral fibers of the ipsilateral (to the microdialysis probe) sciatic nerve produced a significant change only in segmental glycine levels. Contralateral sciatic nerve stimulation failed to evoke a significant elevation of AAs. In addition, a significant increase in the release of glycine and taurine was measured after 90 minutes of transcranial stimulation. SSEP and CMEP components repeatedly showed adequate activation of primary afferent, descending motor fiber pathways, and segmental interneuron pools during dialysis sampling. Our data are consistent with the hypothesis that suprasegmental influence over peripheral afferent and motor activity may be, in part, through these amino acid neurotransmitters in the rabbit lumbar spinal cord.     

Reduced Motor Cortex Deactivation in Individuals Who Suffer from Writer's Cramp

This study investigated the neuromagnetic activities of self-paced finger lifting task and electrical median nerve stimulation in ten writer''s cramp patients and fourteen control subjects. The event-related de/synchronizations (ERD/ERS) of beta-band activity levels were evaluated and the somatosensory cortical activity levels were analyzed using equivalent-current dipole modeling. No significant difference between the patients and control subjects was found in the electrical stimulation-induced beta ERS and electrical evoked somatosensory cortical responses. Movement-related beta ERD did not differ between controls and patients. Notably, the amplitude of the beta ERS after termination of finger movement was significantly lower in the patients than in the control subjects. The reduced movement-related beta ERS might reflect an impairment of motor cortex deactivation. In conclusion, a motor dependent dysregulation of the sensorimotor network seems to be involved in the functional impairment of patients with writer''s cramp.     

The neural basis of tactile texture perception

Running our fingers across a textured surface gives rise to two types of skin deformations, each transduced by different tactile nerve fibers. Coarse features produce large-scale skin deformations whose spatial configuration is reflected in the spatial pattern of activation of some tactile fibers. Scanning a finely textured surface elicits vibrations in the skin, which in turn evoked temporally patterned responses in other fibers. These two neural codes—spatial and temporal—drive a spectrum of neural response properties in somatosensory cortex: At one extreme, neurons are sensitive to spatial patterns and encode coarse features; at the other extreme, neurons are sensitive to vibrations and encode fine features. While the texture responses of nerve fibers are dependent on scanning speed, those of cortical neurons are less so, giving rise to a speed invariant texture percept. Neurons in high-level somatosensory cortices combine information about texture with information about task variables.     

Raphe Stimulation-Evoked Modulation of Postsynaptic Responses by Neurons of the Cat Somatosensory Cortex Activated by Stimulation of Nociceptors

We studied the effects of electrical stimulation of the raphe nuclei (RN) of the cat brain on postsynaptic potentials developing in somatosensory cortex neurons activated by nociceptive influences. Intracellular records were obtained from 15 cells, which were either selectively excited by stimulation of nociceptors (intense electrical stimulation of the dental pulp) or activated by both the above nociceptive and non-nociceptive (moderate stimulations of the infraorbital nerve or thalamic ventroposteromedial nucleus, VPMN) influences. In neurons of both groups, stimulation of both nociceptive afferents and the VPMN evoked complex responses (EPSP–AP–IPSP; IPSPs were 200 to 300 msec long). In some studied cortical neurons, isolated electrical stimulation of the RN (which caused the release of serotonin, 5-HT, in the cortex) resulted in relatively short-latency synaptic excitation, while inhibition was observed in other cells. In the case where stimulation of the RN was used as conditioning influence, such stimulation (independently of the kind of the initial response to RN stimulation) led to long-latency and long-lasting suppression of all components of the synaptic reactions evoked by excitation of nociceptors. The maximum of inhibition was observed at test intervals of 300 to 800 msec. The mechanisms underlying modulatory influences coming from the 5-HT-ergic brainstem system to neurons of the somatosensory cortex, which are activated by excitation of high-threshold (nociceptive) afferent inputs, are discussed.     

Some physiological characteristics of myelinated and unmyelinated fibers with very low conduction velocity

The compound action potential arising in response to supramaximal stimulation of Aδ- or C-fibers of a cat cutaneous nerve (the saphenous nerve) was investigated by methods improving the signal/noise ratio in the record of the unit evoked response. By the use of optical and computer (BÉSM-3M) methods of coherent signal accumulation followed by averaging, potentials of nerve fibers ranging in amplitude from 20 to 0.05 µV and in duration from 10 to 0.4 msec were distinguished from the apparatus noise. A continuous distribution of nerve fibers by conduction velocity was found over the range from 80 to 0.15 m/sec. The conditions of appearance of low-amplitude action potentials of nerve fibers with a low conduction velocity are discussed.     

Changes in amplitude and temporal characteristics of evoked potentials in the sensomotor cortex after division of the spinocervical tracts in cats

Temporal and amplitude characteristics of evoked potentials of the sensomotor cortex in waking cats were studied during variation in the intensity of electrodermal stimulation. The results obtained in experiments on intact animals and on the same animals for several months after division of the spinocervical tracts at the cervical level were compared. After blocking of the inflow of afferent impulses along these tracts of the spinal cord, statistically significant changes in evoked potentials were observed, mainly in response to medium and strong stimulation. These changes were more clear in the motor and second somatosensory areas of the cortex. A decrease in sensitivity to pain also was found. During recovery of the motor functions, cutaneous sensation remained impaired and the amplitude characteristics of the evoked somatosensory activity were not restored. The results suggest that thinner fibers predominate among the primary afferent fibers of the spinocervical tract, and their projections are more widely represented in the second somatosensory and motor areas of the cortex.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 516–523, September–October, 1972.     

Developmental onset of functional activity in the wallaby whisker cortex in response to stimulation of the infraorbital nerve

This study used the extrauterine development of a marsupial wallaby to investigate the onset of functional activity in the somatosensory pathway from the whiskers. In vivo recordings were made from the somatosensory cortex from postnatal day (P) 55 to P138, in response to electrical stimulation of the infraorbital nerve supplying the mystacial whiskers. Current source density analysis was used to localize the responses within the cortical depth. This was correlated with development of cortical lamination and the onset of whisker-related patches, as revealed by cytochrome oxidase. The earliest evoked activity occurred at P61, when layers 5 and 6 are present, but layer 4 has not yet developed. This activity showed no polarity reversal with depth, suggesting activity in thalamocortical afferents. By P72 synaptic responses were detected in developing layer 4 and cytochrome oxidase showed the first hint of segregation into whisker-related patches. These patches were clear by P86. The evoked response at this age showed synaptic activity first in layer 4 and then in deep layer 5/upper layer 6. With maturity, responses became longer lasting with a complex sequence of synaptic activity at different cortical depths. The onset of functional activity is coincident with development of layer 4 and the onset of whisker-related pattern formation. A similar coincidence is seen in the rat, despite the markedly different chronological timetable, suggesting similar developmental mechanisms may operate in both species.