Functional organization of auditory projections to somatosensory cortical areas in cats

The functional properties of fibers transmitting auditory impulses to somatosensory areas S_I and S_II were studied in anesthetized and waking animals by the evoked potentials method. The thresholds of evoked potentials in areas S_I and S_II are 15–35 dB higher than those of evoked potentials in the auditory projection areas. Tonotopical localization is absent in somatic areas. Experiments on anesthetized animals showed that the spread of impulses relating to acoustic stimuli of different frequencies into areas S_I and S_II is effected through area A_I and its connections with the above zones. Another pathway probably also participates in the conduction of impulses from clicks. Analysis of the time constants of the first positive potential suggested that the interneuronal organization of auditory projections to area A_I is less complex than that of projections to the somatosensory areas. Comparison of amplitudes of evoked potentials of different projection zones in area S_I showed that the projection of the head receives more auditory impulses than the projection zone of the forelimbs, confirming the morphological data published previously.     

Cerebral chemosensory evoked potentials elicited by chemical stimulation of the human olfactory and respiratory nasal mucosa

A stimulation method was employed by which chemosensory evoked potentials were recorded without tactile somatosensory contamination. The purpose of the study was to determine whether potential components evoked by stimulation of the chemoreceptors of the trigeminal nerve can be distinguished from those of the olfactory nerve. The stimulants (vanillin, phenylethyl alcohol, limonene, menthol, anethol, benzaldehyde, carbon dioxide and a mixture of vanilin and carbon dioxide) were presented in a randomized order to 13 volunteers. Chemosensory evoked potentials to substances which anosmics are unable to perceive (vanillin, phenylethyl alcohol) were termed olfactory evoked potentials; potentials to CO₂, which effected no olfactory sensations were termed chemo-somatosensory potentials. Analysis of variance revealed that the different substances resulted in statistically significant changes in the amplitudes and latencies of the evoked potentials, and also in the subjective estimates of intensity. An increased excitation of the somatosensory system resulted in reduced latencies and enhanced amplitudes of the evoked potentials. Responses to the mixture of carbon dioxide and vanillin appeared significantly earlier (50–150 msec) than responses to either substance alone.     

Effects of timing of inspiratory occlusion on cerebral evoked potentials in humans

Previous studies from these laboratories have shown that airway occlusion applied from the onset of inspiration or during midinspiration is associated with cerebral evoked potentials in human subjects. The hypothesis tested in the present study was that the more abrupt decrease in mouth pressure produced by midinspiratory occlusion will be associated with evoked potentials that have shorter peak latencies and greater peak amplitudes than those produced by occlusions from the onset of inspiration. The second objective of the present study was to determine whether there is bilateral projection of inputs from the respiratory system to the somatosensory cortex. Random presentation of 64 midinspiratory occlusions and 64 occlusions from the onset of inspiration was performed in eight subjects. The inspirations preceding the occlusions served as control. Evoked potentials were recorded from the scalp with electrode pairs Cz-C3 and Cz-C4. Reaction time to each type of occlusion was measured from the burst in electromyogram activity produced by contraction of the muscles encircling the eye. Each type of inspiratory occlusion was associated with evoked potentials that could be recorded bilaterally. The peak amplitudes of the evoked potentials recorded over the right cerebral hemisphere were significantly greater than those recorded from the left side. The peak amplitude was greater and the peak latency shorter for the evoked potentials produced by the midinspiratory occlusions. The results are consistent with the hypothesis that afferents mediating these potentials are stimulated by added loads to breathing and project bilaterally to the somatosensory cortex in humans.     

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

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

Relation of unit spike discharges and evoked potentials in the auditory cortex of cats.

Extracellular microelectrode recordings were made from the auditory cortex of anaesthetized cats during acoustic click stimulation. The microelectrode of low resistance allowed to record evoked field potentials and unit discharges simultaneously. In distant extracellular leads the relation of unit discharges and field potentials was equivocal. Near extracellular leads revealed that the antidromic invasion of the somadendritic membrane by excitation is a frequency dependent process (just as evoked field potentials) while spike potentials can reliably be elicited from the initial segment at high frequencies. It is assumed that the excitation spreading from the initial segment to the soma-dendritic membrane represents an important component of the evoked potentials, and their frequency dependence may be traced back to inhibitions activated by afferent impulses.     

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.     

Pyramidal tract function during onset of brain death

In 51 patients with primary brain lesions, who fulfilled the criteria of brain death, sequential recording of transcranial magnetic evoked potentials (TMEPs) and somatosensory evoked potentials (SEPs) were performed.In all comatose patients with apnoeic cranial nerve areflexia the TMEP could not be elicited, while the response after cervical magnetic stimulation was always preserved. Similarly, no cortical SEPs were preserved in apnoeic cranial nerve areflexia; however, the cervical somatosensory response was preserved in 44%.In deteriorating patients with coma grade III TMEPs were preserved in 3 instances, while cortical SEPs were already absent. Current brain death criteria, however, were not challenged, as TMEPs were absent in all 51 patients, at the latest when apnoea was noted.     

Interactions of somatosensory evoked potentials: simultaneous stimulation of two nerves

To analyse the mechanism by which sensory inputs are integrated, interactions of somatosensory evoked potentials (SEPs) in response to simultaneous stimulation of two nerves were examined in 12 healthy subjects. Right, left and bilateral median nerves were stimulated in random order so that a precise comparison could be made among the SEPs. The arithmetical sum of the independent right and left median nerve SEPs was almost equal within 40 msec of stimulus onset to that evoked by the simultaneous stimulation of bilateral median nerves. However, a difference emerged after 40 msec. The greatest difference was recorded after 100 msec. Sensory information from right and left median nerves may interact in the late phase of sensory processing. Left median, left ulnar, and both nerves together were stimulated. The sum of the SEPs of left median and ulnar nerves was not equal to that evoked by the simultaneous stimulation of the two nerves even at early latencies. Differences between them were first recorded at 14–18 msec and became greater after 30–40 msec. It is suggested that the neural interactions between impulses in the median and ulnar nerves begin below the thalamic level.     

The role of GABAA and GABAB receptors in formation of evoked potentials in the barrel cortex of rats

By means of local microapplication of GABA, picrotoxin and CGP 52432, different roles of GABAA and GABAB receptors in the geneses of primary and secondary components of evoked potentials in the somatosensory barrel cortex of rats were shown. The authors conclude that the aftereffect rhythmical components of the evoked potentials are caused by the local pacemaker mechanisms based on endogene properties of barrel neurons.     

Characteristics of evoked potentials and single neuron responses in the cat sensorimotor cortex to sound stimuli with different frequencies.

The characteristics of the averaged evoked potentials (AEP) (experiments with awake non-paralysed animals), of the evoked potentials (EP) and of the responses of single sensorimotor cortical neurons (acute experiments) of cats to tone-bursts with frequencies within 0.1-6.0 kHz were studied. Response selectivity to the tone-burst frequencies which are energetically pronounced in some biologically significant sounds for the cat was observed. The averaged curve of the dependence of the amplitude of AEP in the somatosensory cortical region (S1) on the tone-burst frequency has reliable maximum values at the frequencies of 0.8, 1.6 and 2.0-3.0 kHz. Most pronounced changes in the heart rhythm were observed within the tone-burst frequency ranges in which the AEP of the highest amplitudes were recorded. The amplitude of the AEP was found to increase during the conditioned reflex elaboration. The curve of the dependence of the probability of the EP occurrence on the frequency at equal sound pressure levels had maximum values at the frequencies of 1.6 and 3.2 kHz. The highest amplitude values of EP were found at frequencies of 0.8, 1.6 and 3.2 kHz. More than half of the recorded neurons revealed the lowest values of the response thresholds and the maximum values of the occurrence probability under suprathreshold stimulation at frequencies close to 0.8, 1.6, and 3.2 kHz. It is supposed that the above mentioned feature of the input frequency organization in sensorimotor cortex is connected with the selectivity as to the biological significance of acoustic stimuli.     

The frequency dependence of evoked and postsynaptic potentials in the somatosensory cortex of the cat.

Intracellular records were made from neurones of the somatosensory cortex of cats, during stimulation of the ventrobasal complex of the thalamus. The aim of the experiments was to detect correlations between frequency dependence of surface evoked potentials and that of unit discharges. The amplitude of the surface evoked potential showed a strong diminution when the frequency of the thalamic stimulation was raised from 1 cps to 15 cps. In spite of this, frequency dependence in amplitude of unit discharges was never seen. As regards their frequency of occurrence the unit responses (full spikes, dendritic, postsynaptic potentials) behaved differently: a part of them showed increasing, another part gave decreasing occurrence, and the remaining portion did not change it. The authors conclude that temporal dispersion fails to give account for the frequency dependence, therefore further possibilities have to be examined.     

Modification of median nerve somatic evoked potentials by prior median nerve,peroneal nerve,and auditory stimulation

In a recovery function design, changes were measured in the somatic evoked potentials (SEP) to right median nerve (RMN) shocks preceded by stimulation of: the same nerve (RMN-RMN); the left median nerve having primary input to the homologous sensory area in the contralateral hemisphere (LMN-RMN); the right peroneal nerve having primary input to a different region of the same hemisphere (RPN-RMN); and the auditory nerve with primary input to a different sensory modality (AUD-RMN). Eight inter-stimulus intervals ranged from zero (simultaneous) to 2.5 sec. It was assumed that the degree of interaction between evoked potentials would be related to the degree to which common neural structures are activated or modulated in response to the stimuli. Results were: (a) the primary somatosensory response N20-P30 was little influenced by other somatic or auditory stimulation, interaction occurring predominantly in the RMN-RMN condition; (b) with increasing latency, components showed increasing interaction across modalities; (c) preceding homolateral stimulation (RPN-RMN) showed no greater interaction than preceding contralateral stimulation (LMN-RMN); (d) N55-P100 differed from the primary somatosensory response N20-P30 by showing greater interaction with other somatic stimuli; and (e) N140-P190 showed similarly shaped recovery functions across stimulus pairs but significant differences in magnitude of interaction. These results show that components with similar wave form and topographical characteristics can have different neurophysiological properties.     

Changes in the Threshold of Generation of Action Potentials by Spinal Motoneurons under Conditions of Their Natural Activation

We estimated the peculiarities of changes in the threshold of generation of action potentials (APs) by spinal motoneurons (MNs) related to increases in the frequency of discharges evoked by adequate somatosensory stimulation. In experiments on decerebrated cats, we intracellularly recorded the membrane potential (MP) from MNs of the mm. gastrocnemius + soleus. Natural activation of MNs was provided by controlled stretching of the homonymous muscles; AP thresholds were measured using the first derivative of changes in the MP and statistical limits of variations of this derivative. In different cases, the threshold could either increase or decrease with a rise in the frequency; moreover, oppositely directed changes in the threshold could be observed in some MNs within different phases of stretch-evoked activities of these cells. Dissimilarities of the dependences of the thresholds on the AP frequency were clearly manifested in the case of short-lasting increases in the excitability of the MNs, which were usually observed at the beginning of microelectrode recording. We conclude that, under conditions of natural activation of spinal MNs, the pattern of modulation of the AP threshold upon different intensities of excitation is not strictly determined.     

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

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

The effects of neck flexion on cerebral potentials evoked by visual,auditory and somatosensory stimuli and focal brain blood flow in related sensory cortices

Background

A flexed neck posture leads to non-specific activation of the brain. Sensory evoked cerebral potentials and focal brain blood flow have been used to evaluate the activation of the sensory cortex. We investigated the effects of a flexed neck posture on the cerebral potentials evoked by visual, auditory and somatosensory stimuli and focal brain blood flow in the related sensory cortices.

Methods

Twelve healthy young adults received right visual hemi-field, binaural auditory and left median nerve stimuli while sitting with the neck in a resting and flexed (20° flexion) position. Sensory evoked potentials were recorded from the right occipital region, Cz in accordance with the international 10–20 system, and 2 cm posterior from C4, during visual, auditory and somatosensory stimulations. The oxidative-hemoglobin concentration was measured in the respective sensory cortex using near-infrared spectroscopy.

Results

Latencies of the late component of all sensory evoked potentials significantly shortened, and the amplitude of auditory evoked potentials increased when the neck was in a flexed position. Oxidative-hemoglobin concentrations in the left and right visual cortices were higher during visual stimulation in the flexed neck position. The left visual cortex is responsible for receiving the visual information. In addition, oxidative-hemoglobin concentrations in the bilateral auditory cortex during auditory stimulation, and in the right somatosensory cortex during somatosensory stimulation, were higher in the flexed neck position.

Conclusions

Visual, auditory and somatosensory pathways were activated by neck flexion. The sensory cortices were selectively activated, reflecting the modalities in sensory projection to the cerebral cortex and inter-hemispheric connections.     

痛觉诱发电位的研究进展

痛觉诱发电位的研究在过去的几十年内取得了重要进展 ,出现了许多用于被试的诱发明确疼痛感的刺激技术 ,并与诱发电位方法学联合应用 ,已经成为脑映像学研究中重要的组成部分。本文从刺激技术、痛觉诱发电位成分分析和偶极子源分析等方面出发 ,讨论了痛觉诱发电位的研究进展     

Saccular potentials of the vocal plainfin midshipman fish, <Emphasis Type="Italic">Porichthys notatus</Emphasis>

The plainfin midshipman fish, Porichthys notatus, is a vocal species of teleost fish that generates acoustic signals for intraspecific communication during social and reproductive behaviors. All adult morphs (females and males) produce single short duration grunts important for agonistic encounters, but only nesting males produce trains of grunts and growls in agonistic contexts and long duration multiharmonic advertisement calls to attract gravid females for spawning. The midshipman fish uses the saccule as the main acoustic endorgan for hearing to detect and locate vocalizing conspecifics. Here, I examined the response properties of evoked potentials from the midshipman saccule to determine the frequency response and auditory threshold sensitivity of saccular hair cells to behaviorally-relevant single tone stimuli. Saccular potentials were recorded from the rostral, medial and caudal regions of the saccule while sound was presented by an underwater speaker. Saccular potentials of the midshipman, like other teleosts, were evoked greatest at a frequency that was twice the stimulus frequency. Results indicate that midshipman saccular hair cells of non-reproductive adults had a peak frequency sensitivity that ranged from 75 (lowest frequency tested) to 145 Hz and were best suited to detect the low frequency components (≤105 Hz) of midshipman vocalizations.     

A combined electrophysiological and behavioural study for the assessment of activity-dependent changes in mice

Activity-dependent adaptive changes in the nervous system involve structural and functional changes in the cortical circuitry. In this work the cortical function was studied by repeated recording of the somatosensory and motor potentials evoked by whisker deflections after altered sensory-motor experience in adult mice. The latencies of motor and somatosensory evoked potentials were found to shorten, while their amplitudes decreased, after a behavioural challenge involving the vibrissal apparatus. Sensory deprivation achieved by whisker trimming resulted in a partial reversal of the changes observed after increased activity. The derived parameters imply that cortical information processing speeds up as a result of experience, while decreased activity has the opposite effect. The methods used throughout the experiment were minimally invasive, and thus proved to be sufficient for the long-term follow-up of cortical functions.     

Functional organization of the kinesthetic projections of the 1st somatosensory region of the cat cortex

Electrophysiological studies were performed on adult cats under ethaminal anesthesia. Kinesthetic potentials were evoked by passive extension of the ulnar joint and recorded in contralateral primary somatosensory cortical area. Natural (nonelectrical) stimulation of peripheral kinesthetic receptors was performed according to the author's original method. The results obtained show significantly shorter latent period of contralateral kinesthetic potentials in comparison with somatosensory potentials in response to electrical stimulation of the skin. These data demonstrate the possibility of super-rapid conduction of modal-specific volleys to the cortical projection centres in the kinesthetic system of cats.     

Somatosensory Event-related Potentials from Orofacial Skin Stretch Stimulation

Cortical processing associated with orofacial somatosensory function in speech has received limited experimental attention due to the difficulty of providing precise and controlled stimulation. This article introduces a technique for recording somatosensory event-related potentials (ERP) that uses a novel mechanical stimulation method involving skin deformation using a robotic device. Controlled deformation of the facial skin is used to modulate kinesthetic inputs through excitation of cutaneous mechanoreceptors. By combining somatosensory stimulation with electroencephalographic recording, somatosensory evoked responses can be successfully measured at the level of the cortex. Somatosensory stimulation can be combined with the stimulation of other sensory modalities to assess multisensory interactions. For speech, orofacial stimulation is combined with speech sound stimulation to assess the contribution of multi-sensory processing including the effects of timing differences. The ability to precisely control orofacial somatosensory stimulation during speech perception and speech production with ERP recording is an important tool that provides new insight into the neural organization and neural representations for speech.