Tonic inhibitory effect of the cat brain on spinal interneurons

Cord dorsum potentials were recorded in the acute experiments on cats. The relationship between the N-component of the cord dorsum potentials and the strength of stimulation of the big femoral nerve was studied. After the transsection of the half of midbrain tegmentum the increased curve slope indicating the rise in cord interneuron excitability was mainly observed on the contralateral side. The same results were observed after the removal of the contralateral somatosensory cortex or contralateral section of midbrain basis. The data indicate the tonic inhibitory influence of cortical structures on cord interneurons, which participate in the transmission of somatosensory signals.     

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.     

Reflection of the magnitude of the arm rotation angle by the time parameters of kinesthetic evoked cortical potentials in rhesus macaques

The electrophysiological experiments were carried out on five male macaques rhesus under nembutal anesthesia. Kinesthetic evoked potentials in response to arm rotation in the elbow joint were registered in the contralateral primary somatosensory cortex. The data obtained show a significant increase in the duration of kinesthetic potential first positive component with 10 degrees-40 degrees arm rotation amplitude, as compared to 2 degrees rotation. On the contrary, the latent period and amplitude of the component in this stimulation range (2 degrees-40 degrees) were similar. It is suggested that the increase in the arm rotation angle is selectively reflected in the temporary parameters of kinesthetic potential first positive component.     

Cortical potentials evoked by mechanical stimulation of different number of vibrissae of the rat

Distribution maps of cortical potentials evoked by mechanical stimulation of different number of contralateral vibrissae were studied. It was found that stimulation of all the contralateral vibrissae led to more extensive activation than the barrel field in the somatosensory cortex. The activation was most widespread when all the vibrissae were synchronously deflected. With reduction of the number of synchronously stimulated whiskers the activated cortical area did not decrease in parallel. Deflection of only a few whiskers activated significantly smaller cortical areas.     

The effect of stimulation of the deep layers of somatosensory zones CI and CII on the activity of motor zone MI of the cat cortex]

The influence of electrical stimulation of deep layers of the somatosensory zones CI and CII on unit responses and intercortical evoked potentials (IEP) in the motor cortical zone MI in projection areas of the anterior contralateral limb was studied in cats anaesthetized with Nembutal and immobilized with diplacine. Latencies of the main IEP components and their different behaviour during repeated stimulation, experimental hypoxia and Nembutal administration suggested the presence of intercortical connections of an oligo- and polysynaptic nature. Only 22% of the MI zone units proved to be responsive to CI and CII stimulation; the latencies of the unit discharges varied from 4.3 to 35 msec. A relatively smaller effectiveness of short-latency inputs from CI and CII to MI was recorded as compared with long latency ones.     

The role of positive and negative angular accelerations in the genesis of early components of kinesthetic evoked potentials of the first somatosensory area in cats and rhesus monkeys

Studies have been made on the input of negative and positive angular accelerations in the genesis of early complex of positive waves of kinesthetic evoked potentials in contralateral somatosensory cortex. It is suggested that the initial and final phases of these potentials play key role in the origin of the early complex of waves.     

Influence of acute cerebellar lesions on somatosensory evoked potentials (SEPs) in cats.

We studied the effect of acute unilateral cerebellar lesions on the cerebello-thalamo-cortical projection in cats. The lesions were classified into two groups according to their extent. In group I the lesion only covered the cerebellar cortex, while in group II both the cerebellar cortex and deep cerebellar nuclei were removed. Early (short-latency) and late (long-latency) waves, evoked by an electrical stimulation of a forelimb, were collected contralateral to the stimulated leg hemisphere. Pre- and postsurgery recordings from primary and non-primary (motor and parietal) cortices were compared. Cerebellar impairment had a strong influence on discharges of all the considered cortical areas. Early non-primary and primary responses increased in group I and remained unchanged in group II. Late somatosensory evoked potentials components were suppressed in both groups. An inhibitory influence of the cerebellar cortex on the thalamo-cortical projection was confirmed. Changes within the primary sensory cortex may suggest an engagement of that area in the compensation process of cerebellar dysfunction shortly after cerebellar lesion. An alteration in the unaffected hemisphere activation indicate that the spino-cerebellar and cerebello-cortical inputs, responsible for somatosensory evoked potentials generation, are regulated through contralateral and ipsilateral pathways. These pathways are unmasked by cerebellar lesion.     

Lithium effects on the somatosensory cortical evoked response in the rat and cat

The early positive cortical evoked potential to somatosensory stimuli is regularly increased in amplitude in patients receiving lithium carbonate treatment. This may reflect a unique neurochemical effect of lithium since similar changes have not been observed in humans following other drugs. To investigate this finding, cortical evoked potentials to peripheral somatosensory stimulation were obtained in rats and cats with implanted epidural electrodes. In rats, increasing doses of oral lithium chloride, up to 5 meq/kg/d which approached the LD 50, produced no reliable change in the early positive evoked response amplitude. In cats, an increased amplitude of the early positive-negative cortical potential was observed in every instance and the serum lithium levels were within the range used clinically in humans. The increased cortical evoked response amplitude in cats did not directly correlate with serum lithium levels but was delayed 1 to 5 days after serum lithium levels reached their peak. The findings in cats are similar to the human studies. The negative results observed in rats may reflect important species differences regarding lithium.     

Mesencephalic chronic electrodes in pain patients. An electrophysiological study.

Early components of lemniscal potentials after contralateral median nerve or mechanical stimulus are due to lemniscal pathways, whereas later components, after 70 msec appearing bilaterally and at higher stimulus intensities probably express extralemniscal activity. Evoked potentials in the central gray matter show much smaller amplitudes compared with somatosensory cortical evoked potentials (SSEP). The strongest component is a negative wave after 70--100 msec. Longer conditioning stimulation of the lemniscal system inhibits late components in the median nerve evoked cortical potentials. On the contrary, stimulation of the nonspecific periaqueductal gray matter produces inhibition of early components of cortical SSEP together with facilitation of late components.     

Dynamics of the direction of static connections in the electrical activity of the cerebral cortex in the cat

Data have been obtained on three cats for analysis of statistic connections of electrical activity in the visual, parietal and somatosensory cortical zones during development of evoked potentials to photic signal in these areas, and also in periods previous to photic stimulation and on traces of its action. An increase in shown of the influence of activity in the visual area on that of the somatosensory zone in post-stimulus periods and a sharp increase of two-way connections between these areas against the background of a relative equilibrium of direct and backward connections in trace periods.     

Imaging the spatio-temporal dynamics of supragranular activity in the rat somatosensory cortex in response to stimulation of the paws

We employed voltage-sensitive dye (VSD) imaging to investigate the spatio-temporal dynamics of the responses of the supragranular somatosensory cortex to stimulation of the four paws in urethane-anesthetized rats. We obtained the following main results. (1) Stimulation of the contralateral forepaw evoked VSD responses with greater amplitude and smaller latency than stimulation of the contralateral hindpaw, and ipsilateral VSD responses had a lower amplitude and greater latency than contralateral responses. (2) While the contralateral stimulation initially activated only one focus, the ipsilateral stimulation initially activated two foci: one focus was typically medial to the focus activated by contralateral stimulation and was stereotaxically localized in the motor cortex; the other focus was typically posterior to the focus activated by contralateral stimulation and was stereotaxically localized in the somatosensory cortex. (3) Forepaw and hindpaw somatosensory stimuli activated large areas of the sensorimotor cortex, well beyond the forepaw and hindpaw somatosensory areas of classical somatotopic maps, and forepaw stimuli activated larger cortical areas with greater activation velocity than hindpaw stimuli. (4) Stimulation of the forepaw and hindpaw evoked different cortical activation dynamics: forepaw responses displayed a clear medial directionality, whereas hindpaw responses were much more uniform in all directions. In conclusion, this work offers a complete spatio-temporal map of the supragranular VSD cortical activation in response to stimulation of the paws, showing important somatotopic differences between contralateral and ipsilateral maps as well as differences in the spatio-temporal activation dynamics in response to forepaw and hindpaw stimuli.     

Localization of sensorimotor cortex in neurosurgery by recording of somatosensory evoked potentials

The current method of localizing somatosensory and motor cortex during neurosurgical removal of abnormal tissue is Penfield's method of cortical stimulation. While useful, this method has drawbacks, in particular the need to operate under local anesthesia. Another method of localization, described here, involves intra-operative recording of short-latency somatosensory evoked potentials to stimulation of the contralateral median nerve, from electrodes placed directly on central cortex. Proper localization involves identification of potentials which invert in polarity across the central sulcus, identification of other potentials which are largest in the medial portion of the hand area of somatosensory cortex and do not polarity invert, and determination of the region of maximal potential amplitude. This method of localization works equally well whether the patient is under local or general anesthesia, but it occasionally fails in patients with tumors abutting or invading the hand area of sensorimotor cortex.     

The second somatosensory region of the cat thalamus

Recording focal evoked potentials showed that the second somatosensory region of the cat thalamus is located in the posterolateral part of the ventral posteromedial nucleus. The zone of representation of the hindlimb lies somewhat laterally, posteriorly, and superiorly to the zone of the forelimb. The zone of representation of the mouth lies more medially still. Latent periods of responses arising in both regions of the thalamus to cutaneous stimulation of the contralateral limbs are about equal. Neurons of the second somatosensory region of the thalamus send projections to cortical area S2. It can be concluded from the results that formation of the structure of double representation of the somatosensory systems in the cat is completed at the thalamic level.     

Effect of stimulus rate on the cortical posterior tibial nerve SEPs: a topographic study

We performed topographical mapping of somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation delivered at 2, 5 and 7.5 Hz in 15 healthy subjects. P37 was significantly attenuated at 5 and 7.5 Hz and the N50 component attenuated only at 5 Hz, its amplitude remaining stable for further increases in stimulus frequency. Frontal N37 and P50 potentials showed no significant decrease when the stimulus repetition frequency was changed from 2 to 7.5 Hz. P60 showed an attenuation of the amplitude only at 7.5 Hz. Latency and scalp topographies of all cortical components examined remained uncharged for the 3 stimulus rates tested The optimal stimulus rate for mapping of tibial nerve SEPs was lower than 5 Hz. The distinct recovery function of the contralateral N37-P50 and ipsilateral P37-N50 responses suggests that these potentials arise from separate generators     

Responses of units in the magnocellular part of the medial geniculate body to acoustic and somatosensory stimulation

Responses of 150 neurons in the magnocellular part of the medial geniculate body to clicks and to electrodermal stimulation of the contralateral forelimb were investigated in cats immobilized with myorelaxin. Of the total number of neurons 65% were bimodal, 16.6% responded only to clicks, and 15.4% only to electrodermal stimulation. The unitary responses were excitatory (spike potentials) and inhibitory (inhibition of spontaneous activity). Responses beginning with excitation occurred more frequently to stimulation by clicks than to electrodermal stimulation, whereas initial inhibition occurred more often to electrodermal stimulation. The latent period of the initial spike potentials in response to clicks and to electrodermal stimulation was 5–27 and 6–33 (mean 11.6 and 16.2) msec respectively. Positive correlation was found between the latent periods of spike potentials recorded in the same neurons in response to clicks and to electrodermal stimulation, and also to electrodermal stimulation and to stimulation of the dorsal funiculus of the spinal cord. It is concluded that the magnocellular division of the medial genicculate body is a transitional structure between the posterior ventral nucleus and the parvocellular division of the medial geniculate body, and that in addition, it is connected more closely with the auditory than with the somatosensory system. It is suggested that the somatosensory input into the magnocellular division of the medial geniculate body is formed mainly by fibers of the medial lemniscus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 133–141, March–April, 1978.     

Unit responses of the first and second somatosensory cortical areas to peripheral,thalamic, and cortical stimulation

Unit responses of the first (SI) somatosensory area of the cortex to stimulation of the second somatosensory area (SII), the ventral posterior thalamic nucleus, and the contralateral forelimb, and also unit responses in SII evoked by stimulation of SI, the ventral posterior thalamic nucleus, and the contralateral forelimb were investigated in experiments on cats immobilized with D-tubocurarine or Myo-Relaxin (succinylcholine). The results showed a substantially higher percentage of neurons in SII than in SI which responded to an afferent stimulus by excitation brought about through two or more synaptic relays in the cortex. In response to cortical stimulation antidromic and orthodromic responses appeared in SI and SII neurons, confirming the presence of two-way cortico-cortical connections. In both SI and SII intracellular recording revealed in most cases PSPs of similar character and intensity, evoked by stimulation of the cortex and nucleus in the same neuron. Latent periods of orthodromic spike responses to stimulation of nucleus and cortex in 50.5% of SI neurons and 37.1% of SII neurons differed by less than 1.0 msec. In 19.6% of SI and 41.4% of SII neurons the latent period of response to cortical stimulation was 1.6–4.7 msec shorter than the latent period of the response evoked in the same neuron by stimulation of the nucleus. It is concluded from these results that impulses from SI play an important role in the afferent activation of SII neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 351–357, July–August, 1976.     

Serial recording of sensory,corticomotor, and brainstem-derived motor evoked potentials in the rat

A method is presented for serial recording of corticomotor evoked potentials (CMEPs), brainstem-derived motor evoked potentials (BMEPs), and somatosensory evoked potentials (SEPs) via permanently implanted cranial screws. One screw was positioned posterior to lambda (posterior screw), and two screws were positioned over the cortical hind limb areas (cortical screws). SEPs were elicited by stimulation of the hind paw and recorded from the contralateral cortex. BMEPs were stimulated via the posterior screw and recorded from both hind limbs, whereas CMEPs were elicited by repeated bipolar stimulation of the cortex and recorded from the contralateral hind limb. BMEPs and CMEPs differed in several points and can be considered as completely separate motor evoked potentials. While BMEPs consisted of a prominent negative peak with short latency (5–7.5 ms), CMEPs were represented by polyphasic signals with long latencies (17–22 ms). The cortical origin of the CMEPs was confirmed by transecting the corticospinal tracts, which abolished the CMEPs but spared the BMEPs. SEPs consisted of three consecutive peaks with mean latencies of the initial peak ranging between 15 and 17 ms. Dorsal column transection also abolished SEPs. In healthy rats, all three signals were recorded for six consecutive weeks. Signal parameters did not change significantly within this observation period. Rats tolerated the screws and the repeated measurements very well and no negative affect on animal behavior was noted. Thus, this method allows serial recording of SEPs, CMEPs, and BMEPs in chronic rat models.     

Serial recording of sensory, corticomotor, and brainstem-derived motor evoked potentials in the rat

A method is presented for serial recording of corticomotor evoked potentials (CMEPs), brainstem-derived motor evoked potentials (BMEPs), and somatosensory evoked potentials (SEPs) via permanently implanted cranial screws. One screw was positioned posterior to lambda (posterior screw), and two screws were positioned over the cortical hind limb areas (cortical screws). SEPs were elicited by stimulation of the hind paw and recorded from the contralateral cortex. BMEPs were stimulated via the posterior screw and recorded from both hind limbs, whereas CMEPs were elicited by repeated bipolar stimulation of the cortex and recorded from the contralateral hind limb. BMEPs and CMEPs differed in several points and can be considered as completely separate motor evoked potentials. While BMEPs consisted of a prominent negative peak with short latency (5-7.5 ms), CMEPs were represented by polyphasic signals with long latencies (17-22 ms). The cortical origin of the CMEPs was confirmed by transecting the corticospinal tracts, which abolished the CMEPs but spared the BMEPs. SEPs consisted of three consecutive peaks with mean latencies of the initial peak ranging between 15 and 17 ms. Dorsal column transection also abolished SEPs. In healthy rats, all three signals were recorded for six consecutive weeks. Signal parameters did not change significantly within this observation period. Rats tolerated the screws and the repeated measurements very well and no negative affect on animal behavior was noted. Thus, this method allows serial recording of SEPs, CMEPs, and BMEPs in chronic rat models.     

Somatosensory evoked potentials after stimulation of digital nerves in upper limbs: Normative data

Normative data for somatosensory evoked potentials (SEPs) after stimulation of digital nervesfrom the first, third and fifth digits, which reach the spinal cord through C6, C7 and C8 roots are presented in 20 normal adults. SEP peak latencies and amplitudes are indicated for Erb's point, the level of the seventh and second cervical vertebrae and contralateral cortical hand area.     

Comparison of cortical activation patterns by somatosensory stimulation on the palm and dorsum of the hand

Abstract

Objectives: Little is known about differences of cortical activation according to body location. We attempted to compare brain activation patterns by somatosensory stimulation on the palm and dorsum of the hand, using functional magnetic resonance imaging (fMRI).

Method: We recruited 15 healthy right-handed volunteers for this study. fMRI was performed during touch stimulation using a rubber brush on an area of the same size on the palm or dorsum of the hand. Regions of interest (ROIs) were drawn at the primary sensory–motor cortex (SM1), posterior parietal cortex, and secondary somatosensory cortex.

Results: Group analysis of fMRI data indicated that touch stimulation on the palm resulted in production of more activated voxels in the contralateral SM1 and posterior parietal cortex than on the dorsum of the hand. The most activated ROI was found to be the contralateral SM1 by stimulation of the palm or dorsum, and the number of activated voxels (5875) of SM1 by palm stimulation was more than 2 times that (2282) of dorsum stimulation. The peak activated value in the SM1 by palm stimulation (16.43) was also higher than that of the dorsum (5.52).

Conclusion: We found that stimulation of the palm resulted in more cortical activation in the contralateral SM1 than stimulation of the dorsum. Our results suggested that the palm of the hand might have larger somatotopy of somatosensory representation for touch in the cerebral cortex than the dorsum of the hand. Our results would be useful as a rehabilitation strategy when more or less somatosensory stimulation of the hand is necessary.