Non-painful and painful stimulation of human skin and muscle: analysis of cerebral evoked potentials

The present study compared the cerebral processing of non-painful and painful cutaneous CO₂ laser stimulation and intramuscular electrical stimulation in 11 normal subjects. The overall wave form morphology of the long-latency evoked potentials (EPs) at the central vertex (Cz) was identical and surface topographic mappings of the 21-channel recordings showed similar distributions, suggesting involvement of common neural generators. However, the EPs caused by intramuscular stimulation differed from cutaneous stimulation in several distinct ways. First, the latency of the major positive and negative components were significantly shorter with intramuscular stimulation (N 128–145 ms; P 274–298 ms) compared to cutaneous stimulation (N 235–286 ms; P 371–383 ms) (P<0.001). Second, the peak-to-peak amplitude and root-mean-square values of intramuscular EPs recorded at Cz showed a ceiling effect in the painful range, whereas the laser EPs continued to increase in this range. Third, painful intramuscular, but not non-painful, stimulation caused a frontal activity which not was observed with cutaneous laser stimulation at any intensity. Conduction velocity measurements indicated activation of nociceptive A-delta afferents with cutaneous laser stimulation (10.2±0.2 m/s) and activation of a mixed nerve fiber population with intramuscular electrical stimulation (65.8±25.8 m/s). Differences between laser and intramuscular EPs may be due to different types and origins of activated afferent fibers. Laser EPs can be used specifically to assess cutaneous A-delta fiber function, whereas intramuscular EPs reflect the cerebral processing of a mixed afferent input from muscle tissue.     

Cerebral responses elicited by stimulation of the vesico-urethral junction (VUJ) in diabetics

To investigate the involvement of the visceral afferent nerves in diabetes mellitus, we enrolled 46 male patients in a study, examining the cerebral potentials evoked by stimulation of the vesico-urethral junction (VUJ CEP) and the pudendal (penile CEP) and posterior tibial nerves (tibial CEP). The age range was 23–67 (mean 45.8) years. The epithelial surface of the vesico-urethral junction was stimulated bipolarly with an electrode attached to a specially produced Foley catheter. Cerebral responses were recorded bipolarly at vertex.VUJ CEPs were absent (27 patients) or protracted and/ or of low amplitude (4 patients) (total 31 patients; 67.8%). Penile CEP and/or tibial CEP could be obtained in all cases; however, protracted P1 peak latencies were detected in 15 (32.8%). The abnormalities of VUJ CEP did not correlate with the presence of peripheral neuropathy, while the abnormalities of penile CEP and/or tibial CEP invariably coincided with the presence of peripheral neuropathy. Although neither age nor the duration of diabetes correlated with abnormal CEPs as determined by any of the tests, insulin dependence correlated with abnormal penile CEP and to a lesser extent with VUJ CEP.We conclude that VUJ CEP is informative in evaluating the physiological condition of visceral afferents, and can be used in diagnosis of the early involvement of visceral afferents in diabetes mellitus.     

Cerebral evoked potentials after rectal stimulation

We obtained reproducible cortical evoked potentials (EPs) in response to electrical stimulation of the rectum with 1 Hz frequency. We found 2 distinctly different EPs in response to rectal stimulation. In 5 females, the EP had an early onset latency (mean 26 msec) with multiple positive and negative peaks. In 10 females, the EP had a later onset latency (mean 52 msec) and a trifid configuration, having a very prominent negative peak. The early onset EPs after rectal stimulation appeared very similar to the wave form of the cortical EPs recorded after pudendal nerve stimulation. Finding similar interpeak latencies in the early onset EP after rectal stimulation and the EP after pudendal nerve stimulation suggests that either the same pathway was used or that rectal stimulation also stimulated the pudendal nerve. It appears that we stimulated visceral afferents when we recorded late onset EPs, because the large EP amplitude declined rapidly with faster stimulation rates and also with greater number of averaging, and the sensation threshold was very unstable, all different to somatosensory EPs.     

Long latency transient evoked potentials to rapid random stimulation: responses to single and multiple concurrent stimuli

In EP testing, regular (periodic) stimulation at increasing rates produces progressive fusion of responses into steady-state wave forms. When stimuli are presented randomly in time this fusion does not occur. Medium and long latency transient EPs can be recorded to stimulation at interstimulus intervals which are much shorter than the EP wave form latencies. Individual transient EPs can be obtained to multiple independent stimuli presented concurrently when the stimuli are presented randomly to one another. The ability to obtain responses to rapid stimulation and to multiple independent stimuli provides opportunities for increased efficiency and complexity of testing, particularly involving long latency responses.     

Cerebral potentials evoked by rectal distention in humans

The afferent pathways from the rectum can be stimulated and studied after mechanical distention of the rectum. We studied the rectum-brain axis in 24 healthy young adults. The rectum was stimulated with a rectal balloon using inflation volumes of 10 ml and 30 ml air at a stimulation frequency of 0.167 Hz. Additional studies were carried out with 20 ml distention volumes, random stimulation frequency, and stimulation rates of 0.08 Hz and 0.017 Hz. We found two different cortical EPs. An early onset EP was present in 21 of the 24 subjects. P1 latency shortened significantly with increasing distention volumes, but peak amplitudes did not change significantly with larger distention volumes. A late onset EP was present in all subjects with NI latency of 210 ± 15 msec, PI latency of 316 ± 24 msec, and NII latency of 444 ± 34 msec. The different EPs could be due to stimulation of two different visceral afferent pathways which are present in the same individual, due to stimulation of two different fiber populations or due to simultaneous stimulation of afferents in surrounding structures. EP recording after rectal stimulation might be useful in future studies of patients with abnormal rectal sensation.     

Effects of tetanic stimulation on monosynaptic and dorsal root reflexes in kittens.

The effects of tetanic stimulation of peripheral afferents were examined on monosynaptic reflexes and dorsal root reflexes in kittens of various ages. Concomitantly recorded monosynaptic and dorsal root reflexes resulting from the stimulation of muscle nerves showed similar post-tetanic changes, namely, predominantly post-tetanic depression in neonates and post-tetanic potentiation in older kittens or adults. However, the changes in post-tetanic responses expressed as a percentage of control in dorsal root reflexes were much smaller than those in monosynaptic reflexes. When dorsal root reflexes originating from muscle and cutaneous afferents were compared, dorsal root reflexes from the latter behaved quite differently. For all ages, post-tetanic effects on dorsal root reflexes arising from cutaneous afferents were either insignificant or very small. The possible mechanisms underlying differences in post-tetanic effects from muscle and cutaneous afferents in adults and neonates are discussed.     

Cerebral evoked potentials after stimulation of the posterior urethra in man

Cerebral evoked potentials (EPs) were recorded in 25 neurologically normal subjects aged 22–73 years (mean 44.0) after stimulation of the posterior urethra (PU) and the pudendal nerve. After maximal PU stimulation 2 different configurations of the potential were found. In 12 cases a simple bi-triphasic wave form was recorded while in 12 cases there was a bifid form of the first negative wave. In 1 case identical EPs were recorded after PU and pudendal nerve stimulation.It was concluded that (1) PU stimulation excites fibres in the pudendal nerve at higher stimulation strength, resulting in a bifid wave form of the cerebral evoked potential in some individuals, (2) the most prominent negative peak, N1, with a latency of 102.1 ± 13.2 msec, is the most reproducible part of the PU-evoked potential, (3) the N1 is probably transmitted through Aδ fibres localized in the pelvic nerves, (4) there are differences between individuals concerning pudendal and pelvic nerve involvement in afferent innervation of the urethra.     

Relevance of the callosal transfer in defining the peripheral reactivity of somesthetic cortical neurones

Experiments were performed in 13 chloralose-anaesthetized, curarized cat preparations (monitoring of rectal temperature, heart rate, expired pCO2 and EEG), in order to ascertain whether, and to what extent, the reactivity to ipsilateral skin shocks of the neurones of the anterior ectosylvian and anterior suprasylvian gyri (AEG and ASG, respectively) is dependent on the callosal output of the somatosensory areas of the contralateral hemisphere. Indeed, we knew from previous experiments that a high proportion of AEG and ASG neurones having bilateral peripheral receptive fields (PRFs) can be excited by direct stimulation of the contralateral homonymous areas, and that the callosal fibres originating in the latter carry somesthetic impulses related to contralateral PRFs. A preliminary analysis was carried out on the amplitude and latency relationships between the evoked potentials (EP) recorded simultaneously from the two hemispheres and from the corpus callosum (CC) following stimulation of the forepaw of one side. The results obtained showed good correlations between the onset and development of the EPs picked up from the hemisphere ipsilateral to the stimulated skin, on the one hand, and onset and development of the EPs recorded from the contralateral hemisphere and the corpus callosum, on the other. At a further stage of the experiments, the EPs elicited upon ipsilateral and contralateral skin shocks in the AEG-ASG area have been recorded and averaged before, during and after the reversible inactivation of callosal somesthetic transmission. This was achieved by applying polarizing currents (0.2-1 mA) to the rostral portion of the CC, adequacy and reversibility of this method having been tested by observing, respectively, suppression and prompt restoration of transcallosal EPs and of the asynaptic spiking produced by cortical cells when antidromically invaded from contralateral homotopic cortex. It was seen that during CC blockade the EPs elicited in the AEG-ASG areas did not show any change either in amplitude or time-course if brought about by contralateral peripheral stimulation, whereas those evoked by ipsilateral skin shocks exhibited significant reduction, which was related to the strength of CC polarization and to the reduction of transcallosal EPs. In control experiments similar effects were observed after ablation of somatosensory areas of the hemisphere which send off somesthetic callosal impulses, whereas strychninization of these areas caused effects opposite in sign, i.e., enhancement of the ipsilateral but not of the contralateral EPs in the areas of the untreated hemisphere. By testing the effects of CC polarization on single AEG-ASG neurones, it was observed that the responses of units linked only with contralateral PRFs (Group I; 7 units tested) were unaffected by callosal polarization. The discharges of neurones provided with wide and bilateral PRFs (Group II; 27 units tested) were not affected if elicited by contralateral PRF shocks but were deeply impaired (in 11 neurones out the 27) when provoked by ipsilateral PRF stimulation. The effect consisted chiefly of the disappearance of the first high peak of the PSTHs, and when recording intracellularly graded events, it was mirrored by a large decrease of the postsynaptic excitatory potentials elicited in Group II neurones by ipsilateral PRF shocks. A late scattered histographic component was identified in the PSTHs of such cells, which did not appear to be significantly altered during CC blockade. These effects were observed on the ipsilateral responses of 11 out of the 27 Group II neurones so tested whereas the ipsilateral PSTHs of the remaining 16 Group II neurones either did not undergo significant changes during the callosal blockade or escaped evaluation because of high spontaneous shifts of neural responsiveness. The results are discussed mainly with a view to the possible functional role of the specific somesthetic callosal fibres in defining ipsilateral reactivity for the wide-field cells of the AEG-ASG area.     

The Effects of Localized Inactivation of Somatosensory Cortex,Area 2, on the Cat Motor Cortex

Direct corticocortical afferents to the primary motor cortex (MI) originate in area 2 and area 3a of the primary somatosensory cortex (SI). The functional and morphological characteristics of the two pathways indicate that they relay different sensory signals to MI. The role of area 2 in relaying peripheral information to the cat MI was studied using electrophysiological techniques. Neurons that responded to stimulation of peripheral receptive fields on the contralateral forepaw were identified in MI by extracellular recordings. In area 2 of SI, neurons with the same receptive field modality and location as those in MI were also identified. Field potentials to electrical stimulation of the peripheral receptive field were recorded at the somatotopically matched sites in both MI and SI. Neuronal activity at the recording site in area 2 was blocked by injection of lidocaine, a local anesthetic. Changes in MI and area 2 responses were monitored before and after inactivation of area 2. Neuronal activity near the injection site was abolished, and evoked potentials (EPs) in area 2 were considerably diminished immediately following the injection. In MI, spontaneous activity levels were altered at some sites, but overall these changes were not significant. MI EPs recorded in response to peripheral stimulation were altered, and various patterns of change were noted in the early and late phases of the EPs. Changes often occurred in only one phase of the response. In some EPs, both early and late phases changed, but the direction and magnitude of change in one phase were not always linked to such changes in the other phase. Both increases and decreases in the amplitude and the area of each phase were observed. The morphological characteristics of the projection were reviewed and related to the findings in the study. It is proposed that inherent features of the pathway may account for the variable patterns of change that were observed.     

Somatotopic representation of climbing fiber projections from limb cutaneous afferents to the paramedian lobule of the cat cerebellum

Climbing fiber projections to the cerebellar paramedian lobule were investigated electrophysiologically by stimulation of bilateral superficial radial nerve (SR) and superficial peroneal nerve (SP) in the cat anesthetized with pentobarbitone. In the medial zone of the paramedian lobule, short latency climbing fiber responses to stimulation of the ipsilateral SR were recorded rostrally from the top caudal part of the intermediate folia and short latency responses to stimulation of the ipsilateral SP were obtained caudally from the bottom caudal part of the folia. In the central zone, long latency responses to stimulation of the bilateral SR and SP were obtained. "Four limbs area" in which these responses were recorded was 1.0-1.2 mm in width. Short latency responses to stimulation of the ipsilateral SR were observed rostrally from this area, and short and long latency responses to stimulation of the ipsilateral SP were distributed caudally from this area. In the lateral zone, short and long latency responses to stimulation of the ipsilateral SR were recorded rostrally from the rostral part of the intermediate folia, and long latency responses to stimulation of the ipsilateral SP were observed caudally from the caudal part of the folia. In the most lateral zone, short and long latency responses to stimulation of the ipsilateral SR were obtained rostrally from the rostral part of the intermediate folia, and long latency responses to stimulation of ipsilateral SP were recorded only in the bottom caudal part of the folia caudally from the caudal part of the folia.     

Human group I excitatory projections from ankle dorsiflexors to quadriceps muscle

A short latency projection of group I afferent fibers from ankle dorsiflexors to knee extensor muscles has been categorized as species specific to humans. However, the effects of the pathway have only been inferred from conditioning homonymous reflexes in relaxed muscle. This study focused directly on the responses evoked in the electromyogram of the heteronymous muscles when active, in two experiments. In the first, preferential activation of group I afferents of ankle dorsiflexors, by electrical stimulation of the common peroneal nerve, excited both vastus medialis (mean latency, 26.3 ms) and rectus femoris (mean latency, 33.5 ms). No excitation or inhibition in either muscle was associated with stimulation of the tibial nerve. The second experiment compared vastus medialis responses with common peroneal nerve stimulation during three different movement conditions in which the muscle was equally contracted: rhythmic isotonic (pedalling); episodic isotonic; isometric contraction. Responses were identified in all three active states, with no significant differences in amplitude or latency. No responses were seen in the relaxed muscle.     

Excitation of dorsal and ventral respiratory group neurons by phrenic nerve afferents

The projections of phrenic nerve afferents to neurons in the dorsal (DRG) and ventral (VRG) respiratory group were studied in anesthetized, paralyzed, and vagotomized cats. Extracellular recordings of neuronal responses to vagal nerve and cervical phrenic nerve stimulation (CPNS) indicated that about one-fourth of the DRG respiratory-modulated neurons were excited by phrenic nerve afferents with an onset latency of approximately 20 ms. In addition, non-respiratory-modulated neurons within the DRG were recruited by CPNS. Although some convergence of vagal and phrenic afferent input was observed, most neurons were affected by only one type of afferent. In contrast to the DRG, only 3 out of 28 VRG respiratory-modulated neurons responded to CPNS. A second study determined that most of these neuronal responses were due to activation of diaphragmatic afferents since 90% of the DRG units activated by CPNS were also excited at a longer latency by thoracic phrenic nerve stimulation. The difference in onset latency of neuronal excitation indicates an afferent peripheral conduction velocity of about 10 m/s, which suggests that they are predominately small myelinated fibers (group III) making paucisynaptic connections with DRG neurons. Decerebration, decerebellation, and bilateral transection of the dorsal columns at C2 do not abolish the neuronal responses to cervical PNS.     

Development of the hypothalamic-cortical interrelations in the ontogeny of the cat

Under chloralose narcosis, employing the evoked potentials method, studies have been made on the projection of the posterior hypothalamus to the frontal cortex in 1-30 days old kittens. The animals were divided into 3 age groups: 1-9, 10-19 and 20-30 days. Studies of the EPs in different points of pericruciate zone showed that these potentials are observed in all the investigated points from the first days of postnatal life. The latent period of responses in the youngest animals varied from 40 to 80 ms, exhibiting insignificant fluctuations depending on the cortical zone investigated. From the very beginning of postnatal life, in the same cortical zone the EPs may be observed in response to stimulation of the ischiadic nerve as well. In older animals, the latent period of the EPs decreases in all the points, the decrease being most significant near the crucial fissure. To the 30th day of postnatal life, the EPs in this zone with respect to their latency and configuration became quite similar to those in adult animals. In the third age period, the latency varies from 6 to 10 ms in the focus of maximum activity; with the removal of the recording electrode from this zone the latent period of the hypothalamo-cortical responses increases up to 30-40 ms. Overlapping of the EPs in response to central and peripheral stimulation was observed at all age periods.     

The role of the genotype in the variability of human evoked potentials at different stages of ontogeny]

The determinants of individual differences in visual EPs to stimuli of different type depending on the age of subjects were studied. EPs to flash, checkerboard pattern and some other stimuli with semantic aspect were recorded in three groups of MZ, DZ twins aged 8-9, 10-12, 18-25 years. The heritability of EPs parameters is not ontogenetically stable characteristic. It changes from one age group to another in different way for separate EPs components and parameters depending on their nature, type of stimulus, area of recording. Most of all genotypical influences are manifested in EPs parameters of 10-12 years old subjects, especially the middle latency components from vertex area and latent periods of EPs in comparison with their amplitudes.     

Fusimotor reflex profiles of individual triceps surae primary muscle spindle afferents assessed with multi-afferent recording technique.

The experiments were performed on 21 cats anaesthetized with alpha-chloralose. The aim of the study was to investigate sets of simultaneously recorded spindle afferents (2-4 in each set) from the triceps surae muscle (GS) with respect to the pattern of fusimotor reflex effects evoked by different types of ipsi- and contralateral reflex stimulation. The afferents' responses to sinusoidal stretching of the GS muscle were determined and the fusimotor reflex effects were assessed by comparing the afferent responses (i.e. the mean rate of firing and the depth of modulation) elicited during reflex stimulation with those evoked in absence of any reflex stimulus. Natural of electrical activations of ipsi- and contralateral muscle, skin and joint receptor afferents were used as reflex stimuli. The spindle afferents were influenced by several modalities and from wide areas, with a majority responding to both ipsi- and contralateral stimuli. A particular reflex stimulus often caused different effects on different afferents, and the various reflex stimuli seldom gave similar effects on a particular afferent. Multivariate analysis revealed that the variation in response profiles among simultaneously recorded afferents were as great as between afferents recorded on different occasions. This suggests that the individualized response prifiles, observed in earlier investigations, represent a very diversified reflex control of the spindle primary afferents, and are not a reflection of changes in the setting of the spinal interneuronal network, occurring during the time interval between the recordings of different units. Also, there was no relation between the conduction velocity of the afferents and the reflex profiles of the afferents, but non-linear relations were found between effects elicited by different types of stimuli. Indications were also found that it may be possible to separate the population of GS muscle spindles into subgroups, according to the fusimotor effects exhibited by activation of various categories of ipsi- and contralateral receptor afferents. It is concluded that one possible way of making the very complex reflex system controlling the muscle spindles intelligible may be a combination of multiple simultaneous recordings of spindle afferents and multivariate analysis.     

Interaction between segmental and descending intersegmental reflexes in lumbar motoneurons

The effects of segmental reflexes on descending intersegmental reflexes to stimulation of forelimb afferents were studied in anesthetized cats by recording postsynaptic responses from single motoneurons. Interaction between these influences was found to be reciprocal in character for groups of neurons with primary connections with afferents of the superficial and deep branches of the peroneal nerve and afferents of the nerve to the gastrocnemius muscle. Excitatory postsynaptic responses arising in groups of motoneurons of the peroneal nerve to stimulation of forelimb afferents underwent profound and prolonged inhibition during conditioning stimulation of afferents in the deep and superficial peroneal nerves. Activation of segmental afferents during conditioning stimulation of the gastrocnemius nerve was accompanied by inhibition of excitatory intersegmental responses and deinhibition of inhibitory responses in motoneurons of the gastrocnemius muscle. Segmental inhibition of intersegmental descending impulse activity appeared in the interneuron system of the segmental reflex centers connecting the descending propriospinal tracts with the motoneurons of these centers.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 16872-175, March–April, 1972.     

Botzinger complex region role in phrenic-to-phrenic inhibitory reflex of cat

Neuronal recordings, microstimulation, and electrolytic and chemical lesions were used to examine the involvement of the B?tzinger Complex (B?tC) in the bilateral phrenic-to-phrenic inhibitory reflex. Experiments were conducted in decerebrate cats that were paralyzed, ventilated, thoracotomized, and vagotomized. Microelectrode recordings within the B?tC region revealed that some neurons were activated by phrenic nerve stimulation (15 of 69 expiratory units, 9 of 67 inspiratory units, and 19 nonrespiratory-modulated units) at average latencies similar to the onset latency of the phrenic-to-phrenic inhibition. In addition, microstimulation within the B?tC caused a short latency transient inhibition of phrenic motor activity. In 17 cats phrenic neurogram responses to threshold and supramaximal (15 mA) stimulation of phrenic nerve afferents were recorded before and after electrolytic B?tC lesions. In 15 animals the inhibitory reflex was attenuated by bilateral lesions. Because lesion of either B?tC neurons or axons of passage could account for this attenuation, in eight experiments the phrenic-to-phrenic inhibitory responses were recorded before and after bilateral injections of 5 microM kainic acid (30-150 nl) into the B?tC. After chemical lesions, the inhibitory response to phrenic nerve stimulation remained; however, neuronal activity typical of the B?tC could not be located. These results suggest that axons important in producing the phrenic-to-phrenic reflex pass through the region of the B?tC, but that B?tC neurons themselves are not necessary for this reflex.     

Comparison of baroreceptive to other afferent synaptic transmission to the medial solitary tract nucleus

Cranial nerve visceral afferents enter the brain stem to synapse on neurons within the solitary tract nucleus (NTS). The broad heterogeneity of both visceral afferents and NTS neurons makes understanding afferent synaptic transmission particularly challenging. To study a specific subgroup of second-order neurons in medial NTS, we anterogradely labeled arterial baroreceptor afferents of the aortic depressor nerve (ADN) with lipophilic fluorescent tracer (i.e., ADN+) and measured synaptic responses to solitary tract (ST) activation recorded from dye-identified neurons in medial NTS in horizontal brain stem slices. Every ADN+ NTS neuron received constant-latency ST-evoked excitatory postsynaptic currents (EPSCs) (jitter < 192 micros, SD of latency). Stimulus-recruitment profiles showed single thresholds and no suprathreshold recruitment, findings consistent with EPSCs arising from a single, branched afferent axon. Frequency-dependent depression of ADN+ EPSCs averaged approximately 70% for five shocks at 50 Hz, but single-shock failure rates did not exceed 4%. Whether adjacent ADN- or those from unlabeled animals, other second-order NTS neurons (jitters < 200 micros) had ST transmission properties indistinguishable from ADN+. Capsaicin (CAP; 100 nM) blocked ST transmission in some neurons. CAP-sensitive ST-EPSCs were smaller and failed over five times more frequently than CAP-resistant responses, whether ADN+ or from unlabeled animals. Variance-mean analysis of ST-EPSCs suggested uniformly high probabilities for quantal glutamate release across second-order neurons. While amplitude differences may reflect different numbers of contacts, higher frequency-dependent failure rates in CAP-sensitive ST-EPSCs may arise from subtype-specific differences in afferent axon properties. Thus afferent transmission within medial NTS differed by axon class (e.g., CAP sensitive) but was indistinguishable by source of axon (e.g., baroreceptor vs. nonbaroreceptor).     

豚鼠肠系膜下神经节细胞电活动与结肠运动的关系

在豚鼠肠系膜下神经节(IMG)及其支配的结肠段联合标本上,对IMG细胞内电位与肠段纵肌或环肌舒缩活动进行了同步记录。实验结果表明:(1)肠段预置张力为零时,约50％IMG细胞有自发的快兴奋性突触后电位(EPSP)活动,切断结肠神经或以筒箭毒(50μmol/L)灌流IMG后消失;(2)筒箭毒或低钙高镁溶液阻断神经节传递时,环肌节律性收缩幅度增大,节律变慢,但对纵肌节律性收缩无明显影响,(3)串刺激节前神经,在IMG细胞引起一串快EPSP或动作电位并常跟随迟慢的EPSP,同时,纵肌在0.1-0.2s潜伏期后出现迅速的、时程基本与动作电位串一致的舒张波,后者在筒箭毒灌流IMG后消失,而环肌运动可见舒张、舒张波延长或收缩波增大。结果提示:IMG不仅中继经典的胆碱能传出功能,还参与以胆碱能传递为中介的肠-肠反射,该反射活动的传出效应主要在于抑制环肌收缩。     

The Primary Visual Cortex Is Differentially Modulated by Stimulus-Driven and Top-Down Attention

Selective attention can be focused either volitionally, by top-down signals derived from task demands, or automatically, by bottom-up signals from salient stimuli. Because the brain mechanisms that underlie these two attention processes are poorly understood, we recorded local field potentials (LFPs) from primary visual cortical areas of cats as they performed stimulus-driven and anticipatory discrimination tasks. Consistent with our previous observations, in both tasks, we found enhanced beta activity, which we have postulated may serve as an attention carrier. We characterized the functional organization of task-related beta activity by (i) cortical responses (EPs) evoked by electrical stimulation of the optic chiasm and (ii) intracortical LFP correlations. During the anticipatory task, peripheral stimulation that was preceded by high-amplitude beta oscillations evoked large-amplitude EPs compared with EPs that followed low-amplitude beta. In contrast, during the stimulus-driven task, cortical EPs preceded by high-amplitude beta oscillations were, on average, smaller than those preceded by low-amplitude beta. Analysis of the correlations between the different recording sites revealed that beta activation maps were heterogeneous during the bottom-up task and homogeneous for the top-down task. We conclude that bottom-up attention activates cortical visual areas in a mosaic-like pattern, whereas top-down attentional modulation results in spatially homogeneous excitation.