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.     

Real-time imaging of neural activity during binaural interaction in the guinea pig auditory cortex

Spatio-temporal patterns of binaural interaction in the guinea pig auditory cortex (AC) were observed using optical recording with a 12 × 12 photodiode array and a voltage-sensitive dye. The amplitudes of the sound-induced light signals from the cortex were transformed into sequential two-dimensional images every 0.58 ms. Binaural sound stimuli evoked an excitatory response followed by a strong inhibition, and contralateral stimuli evoked a strong excitatory response followed by a weak inhibition. Ipsilateral sound stimuli evoked a weak response. Binaural stimulation induced two types of ipsilateral inhibition: a fast binaural inhibition which was detected only after the contralateral and ipsilateral responses were subtracted from the binaural responses, and which appeared 12–25 ms after the onset of stimulation, and a slow binaural inhibitory effect which was clearly observed in the binaural responses themselves, appearing 70–95 ms after the onset of stimulation. The fast binaural inhibition was observed in the same area as the contralateral excitatory response. The inhibited area became stronger and more widespread with increasing intensity of ipsilateral stimulation. We did not observe the specialized organization of binaural neurons as electrophysiologically found in the cat AC, in which binaural neurons of the same binaural response type are clustered together and alternate with clusters of other response types. Accepted: 14 August 1997     

Response properties of auditory activated cells in the occipital cortex of the blind mole rat: an electrophysiological study

Previous studies have demonstrated that despite its blindness, the subterranean blind mole rat (Spalax ehrenbergi) possesses a noticeable lateral geniculate nucleus and a typical cyto-architectural occipital cortex that are reciprocally connected. These two areas, as revealed by the metabolic tracer 2-deoxyglucose, are activated by auditory stimuli. Using single unit recordings, we show that about 57% of 325 cells located within the occipital cortex of anesthetized mole rats responded to at least one of the following auditory stimuli — white noise, pure tones, clicks, and amplitude modulated tones — with the latter two being the most effective. About 85% of cells driven by either contralateral or ipsilateral stimulation also responded to binaural stimulation; about 13% responded only to binaural stimulation; and 2% were driven exclusively by contralateral stimulation. Comparing responsiveness and response strength to these three modes of stimulation revealed a contralateral predominance. Mean latency (±SD) of ipsilateral and contralateral responses were 48.5±32.6 ms and 33.5±9.4 ms, respectively. Characteristic frequencies could be divided into two distinct subgroups ranging between 80 and 125 Hz and between 2,500 and 4,400 Hz, corresponding to the most intensive spectral components of the vibratory intraspecific communication signals and airborne vocalizations.Abbreviations BMF best modulation frequency - CF characteristic frequency - 2-DG 2-deoxyglucose - dLGN dorsal lateral geniculate nucleus - IC inferior colliculus - LGN lateral geniculate nucleus - OC occipital cortex - MTF modulation transfer function - SAM sinusoidally amplitude modulation - SC superior colliculus     

Attenuation of phrenic motor discharge by phrenic nerve afferents

Short latency phrenic motor responses to phrenic nerve stimulation were studied in anesthetized, paralyzed cats. Electrical stimulation (0.2 ms, 0.01-10 mA, 2 Hz) of the right C5 phrenic rootlet during inspiration consistently elicited a transient reduction in the phrenic motor discharge. This attenuation occurred bilaterally with an onset latency of 8-12 ms and a duration of 8-30 ms. Section of the ipsilateral C4-C6 dorsal roots abolished the response to stimulation, thereby confirming the involvement of phrenic nerve afferent activity. Stimulation of the left C5 phrenic rootlet or the right thoracic phrenic nerve usually elicited similar inhibitory responses. The difference in onset latency of responses to cervical vs. thoracic phrenic nerve stimulation indicates activation of group III afferents with a peripheral conduction velocity of approximately 10 m/s. A much shorter latency response (5 ms) was evoked ipsilaterally by thoracic phrenic nerve stimulation. Section of either the C5 or C6 dorsal root altered the ipsilateral response so that it resembled the longer latency contralateral response. The low-stimulus threshold and short latency for the ipsilateral response to thoracic phrenic nerve stimulation suggest that it involves larger diameter fibers. Decerebration, decerebellation, and transection of the dorsal columns at C2 do not abolish the inhibitory phrenic-to-phrenic reflex.     

Whole-head mapping of middle-latency auditory evoked magnetic fields

We recorded middle-latency auditory evoked magnetic fields from 9 healthy subjects with a 122-channel whole-head SQUID gradiometer. The stimuli were click triplets, 2.5 msec in total duration, delivered alternately to the two ears once every 333 msec. Contralateral clicks elicited P30m responses in 16 and P50m responses in 12 out of 18 hemispheres studied; ipsilateral clicks did so in 7 and 13 hemispheres, respectively. The field patterns were satisfactorily explained by current dipoles in 16 and 4 hemispheres for contra- and ipsilateral P30m, and in 4 and 10 hemispheres for contra- and ipsilateral P50m. The peak latencies of P30m and P50m were not affected by stimulation side. The results show that middle-latency auditory evoked responses receive a strong contribution from auditory cortical structures, and that differences of input latency to cortical auditory areas, evaluated from MLAEF latencies, do not explain the latency differences seen in late auditory evoked fields to contralateral vs. ipsilateral stimulation.     

Functional characteristics of the input-output correlation in the frog vestibular nuclei

Field and intracellular potentials were recorded in the vestibular nuclear complex of the frog perfused brain following stimulation of the anterior branch of the ipsilateral vestibular nerve and spinal cord. Mono- and polysynaptic EPSPs with orthodromic APs were recorded from vestibular neurones following vestibular nerve stimulation. Antidromic activation of neurones sending their axons to the labyrinth was also recorded. Antidromic APs of vestibulo-spinal neurones evoked with mean latency of 1.43 and 2.19 ms to stimulation of cervical and lumbar cords, respectively, were revealed.     

Convergence of olfactory inputs from both antennae in the brain of the honeybee.

Electrical activities of the olfactory neurones in the brain of the honeybee were investigated. Odorous stimuli were given to each antenna separately or to both simultaneously. The inputs from the antennae affected both the impulse frequency and the latency of the olfactory interneurones in the protocerebrum. The predominant response was to the stimulation of the ipsilateral antenna. Input from the contralateral antenna produced mainly excitatory effects, although a few inputs gave inhibitory effects. No particular relationships between the loci of the units in the brain and the types of responses produced were found. Most of the units were located in the protocerebral lobe and in the central commissure. The units in the deutocerebrum responded only to the stimulation of the ipsilateral antenna, and the magnitude of response and the latency were not different with respect to unilateral or bilateral stimulation of the antennae. Differences in latency between unilateral and bilateral stimulation were observed in some of the units in the protocerebrum. Neural models which explain these phenomena are postulated.     

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.     

Synaptic transmission in suprasylvian visual cortex is reduced by excitatory amino acid antagonists

The activities of cortical neurones lying in the Clare-Bishop area of the suprasylvian visual region in anaesthetized cats were monitored during the application of cholinergic and amino acid agonists and antagonists, as well as during sequences of light and electrical stimulation. Of those Clare-Bishop cells which could be activated at short latencies by electrical stimuli applied to the contralateral, homologous cortical zone, D-alpha-aminoadipate and 2-amino-5-phosphonovalerate antagonized neuronal responses elicited by electrically evoked synaptic activation and by the presentation of light stimuli. Acetylcholine as well as the excitatory amino acids increased the firing of many of these neurones; however only the amino acid antagonists blocked the commissurally evoked excitations although both types of antagonist reduced the magnitudes of the visually evoked responses. It therefore appears as though the same synaptic transmitter is utilized by cortical commissural afferents as is employed by the cortical ipsilateral projection to the Clare-Bishop area, and furthermore this transmitter is likely to be an excitatory amino acid.     

The effect of selective attention on pattern-specific visual evoked potentials

In a complex choice reaction time experiment, patterned stimuli without luminance change were presented, and pattern-specific visual evoked potentials to lower half-field stimulation were recorded. Two experimental conditions were used. The first was the between-field selection, where square patterns were presented in either the lower or the upper half of the visual field. In a given stimulus run one of the half-fields was task-relevant, and the subjects' task was to press a microswitch to stimuli of higher duration value (GO stimuli), while they had to ignore shorter ones, i. e. stimuli of lower apparent spatial contrast (NOGO stimuli). They had to ignore the stimuli appearing in the irrelevant half-field (IRR stimuli). In order to ensure proper fixation, the subjects had to press another microswitch at the onset of a dim light at the fixation point (CRT stimuli). Our second experimental condition was the within-field selection, where the GO, NOGO, and IRR stimuli appeared in the lower half of the visual field. GO and NOGO were square patterns while IRR stimuli were constructed of circles, or vice versa. (The CRT stimuli were the same as in the previous condition.) Three pattern-specific visual evoked potential components were identified, i. e. CI (70 ms latency), CII (100 ms latency), and CIII (170 ms latency). There were marked selective attention effects on both the CI-CII and CII-CIII peak-to-peak amplitudes. In both experimental conditions, responses with the highest amplitude were evoked by the GO type of stimuli, while the IRR stimuli evoked the smallest responses. According to these results, attention effects on the pattern-specific visual evoked potentials in the first 200 ms cannot be attributed to a simple stimulus set kind of selection.     

Modulation of vibrissa-evoked cortical potentials after infraorbital nerve crush in rats

Cortical potentials evoked by unilateral stimulation of the major vibrissae were recorded in 12 rats subjected to unilateral crush of the infraorbital nerve. Immediately after nerve crushing, the latency of the initial positive potential evoked at contralateral scalp sites by stimulating the vibrissae of the nerve-crushed side was increased. In contrast, the latency of the ipsilaterally evoked potential was shortened. The relative amplitude of the negative component to the positive one of the evoked potentials tended, immediately after the nerve crush, to be smaller on the contralateral cortex (N/P-contra) and greater on the ipsilateral cortex (N/P-ipsi). These changes disappeared largely by the 2nd post-operative week. It is suggested that reduction of the tactile signals transmitted through the crossed pathway is responsible for the prolonged latency and the smaller N/P-contra. Shortening of the ipsilateral latency and the enhanced N/P-ipsi may be due to liberation of the ipsilateral sensory system from inhibition by the contralateral one.     

Ipsilateral median somatosensory evoked potentials recorded from human somatosensory cortex

Somatosensory evoked potentials (SEP) to ipsilateral and contralateral median nerve stimulations were recorded from subdural electrode grids over the perirolandic areas in 41 patients with medically refractory focal epilepsies who underwent evaluation for epilepsy surgery. All patients showed clearly defined, high-amplitude contralateral median SEPs. In addition, four patients showed ipsilateral SEPs. Compared with the contralateral SEPs, ipsilateral SEPs were very localized, had a different spatial distribution, were of considerably lower amplitude, had a longer latency (1.2–17.8 ms), did not show an initial negativity, and were markedly attenuated during sleep. Stimulation of the subdural electrodes overlying the sensory hand area was associated with contralateral hand paresthesias, but no ipsilateral hand paresthesias occurred. It was concluded that subdurally recorded cortical SEPs to ipsilateral stimulation of the median nerve (M) reflect unconscious sensory input from the hand possibly serving fast bimanual hand control. The anatomical pathway of these ipsilateral short-latency MSEPs is not yet known. Transcallosal transmission seems unlikely because of the short delay between the ipsilateral and contralateral responses in selected cases. The infrequent occurrence of ipsilateral subdurally recorded SEPs and their low amplitude and limited distribution suggest that they contribute very little to the short-latency ipsilateral median SEPs recorded on the scalp.     

Rubrofugal activation of motoneurons of the cat accessory nucleus

Postsynaptic potentials evoked in accessory nerve motoneurons by stimulation of the ipsilateral and contralateral red nuclei were investigated in acute experiments on cats anesthetized with chloralose and pentobarbital. Polysynaptic EPSPs with latent periods of 5.2 to 16 (mean 9.1 ± 0.7) msec and from 5.5 to 18 (mean 10.3 ± 0.9) msec, respectively, appeared in motoneurons of the accessory nerve in response to stimulation of the contralateral and ipsilateral red nuclei. A minimum of two or three stimuli was necessary to produce EPSPs in these motoneurons. In response to single stimulation of the contralateral and ipsilateral red nuclei EPSPs appeared in four motoneurons of the trapezius muscle with latent periods of 2.5 to 5.0 and 3.0 to 5.2 msec, respectively. An increase in the number of stimuli led to action potential generation by motoneurons. The functional role of such activation is discussed.A. A. Bogomolets Institue of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 532–536, September–October, 1982.     

Pretecto-tectal influences

(1)From the dorsal surface of the toad (Bufo b. spinosus, B. marinus) optic tectum (OT), field potentials (FP) were recorded at 9 reference sites in response to electrical stimulation of the optic nerve (ON). The FP showed 4 main components, besides an initial deflection attributed to axonal potentials: two negative waves N1, N2 (attributed to postsynaptic excitatory processes) and two positive waves P2, P3 (attributed to postsynaptic inhibitory processes). The responses across the reference sites were rather similar in different individuals. (2) Electrical stimulation of an area in the ipsilateral pretectal lateral posterodorsal and posterior (Lpd/P) thalamic region evoked tectal FPs showing mainly a negative and a positive wave. Regarding wave amplitudes, the FPs displayed disproportionalities across the reference sites. (3) Electrical stimulation of the contralateral Lpd/P evoked mainly a positive wave in the tectal FP whose disproportionality corresponded roughly to the one obtained to ipsilateral Lpd/P stimulation. (4) The inital negative wave of the tectal FP in response to ON stimulation was nearly abolished, if Lpd/P stimulation preceded ON stimulation at a delay of 17–25 ms. (5) Since FPs showed adaptation to repetitive stimulation, various experiments were carried out to distinguish adaptation phenomena from effects of neuronal interactions between Lpd/P and OT. (6) The results provide evidence that ON- and Lpd/P-mediated inputs interact in superficial tectal layers, whereby pretectotectal input suppresses retinotectal excitatory information transfer. Input of Lpd/P to the contralateral superficial OT suggests postsynaptic inhibition. This study provides no information about pretectal inputs to deeper tectal layers, which anatomically are known to exist.Abbreviations A-I recording sites from the dorsal tectal surface - D _t delay between Lpd/P and ON stimulation - EPSP IPSP excitatory and inhibitory postsynaptic potentials, respectively - FP field potential - L latency of FP waves - ON optic nerve - OT optic tectum - Lpd/P lateral posterodorsal and posterior pretectal thalamic region - Lpv lateral posteroventral pretectal thalamic nucleus - N, P negative and positive waves of FPs, respectively - PRE presynaptic axonal input - TH pretectal thalamic neurons     

Development of cortical somatosensory evoked potentials in rats.

The development of the contra- and ipsilateral cortical potential evoked by electrical sciatic nerve stimulation was studied in 77 male albino rats aged 5 to 45 days. A contralateral response was already recorded, as double negativity, in the youngest animals, while an ipsilateral evoked potential was not reliably present until the 10th day. At this time, however, both responses started with an inconstant positive wave and their shape was practically the same. During subsequent development the responses differed only in respect to their dominant component: in the contralateral response, the N1 wave had the highest amplitude for most of the time, while in the ipsilateral response the delayed N2 wave was the largest component. The latent periods of contralateral responses were somewhat shorter than those of ipsilateral evoked potentials. During development we noticed a phase of abrupt shortening of the latent period, which took place before the 15th day in the contralateral response and before the 20th day in the ipsilateral response. We also found a difference in the fatigability of the responses, which was greater in immature rats than in adult animals; in the ipsilateral evoked potential it approached adult values more slowly. The development of the ipsilateral response is thus delayed compared with the development of the contralateral response.     

Evoked responses of the anterior cingulate cortex to stimulation of the medial thalamus

In the present study we characterized the field potentials in the anterior cingulate cortex (ACC) evoked by electrical stimulation of the medial thalamus (MT), and elucidated the synaptic organization of the ACC. Male Sprague Dawley rats were maintained in general anesthesia by alpha-chloralose (50 mg/kg, i.v.). Tungsten micro-electrodes were used for electric stimulation and recordings. The field potentials and multiple unit activities in the ACC were evoked by electric stimulation of the MT where the nociceptive responses were identified. A MT-evoked positive-negative potential was recorded on the medial frontal surface. The polarity of the surface negative potential was reversed between 0.5 to 1.0 mm in the deep layer of the ACC. Maximum evoked negative potential appeared at about 4 mm anterior to the bregma and 1 mm lateral to the midline. The maximum evoked positive potential occurred at about 3 mm anterior to the bregma and 1 mm lateral to the midline. The evoked multiple unit activities coincided with the deep negative field potential at a latency between 16 ms and 24 ms at a depth between 0.5 mm and 1.5 mm in the ACC. These electrophysiological findings confirmed that nociceptive information in the MT is transmitted to the ACC and trans-synaptically activates deeper and more superficial layers of cortical neurons.     

Interlimb Reflexes Induced by Electrical Stimulation of Cutaneous Nerves after Spinal Cord Injury

Whether interlimb reflexes emerge only after a severe insult to the human spinal cord is controversial. Here the aim was to examine interlimb reflexes at rest in participants with chronic (>1 year) spinal cord injury (SCI, n = 17) and able-bodied control participants (n = 5). Cutaneous reflexes were evoked by delivering up to 30 trains of stimuli to either the superficial peroneal nerve on the dorsum of the foot or the radial nerve at the wrist (5 pulses, 300 Hz, approximately every 30 s). Participants were instructed to relax the test muscles prior to the delivery of the stimuli. Electromyographic activity was recorded bilaterally in proximal and distal arm and leg muscles. Superficial peroneal nerve stimulation evoked interlimb reflexes in ipsilateral and contralateral arm and contralateral leg muscles of SCI and control participants. Radial nerve stimulation evoked interlimb reflexes in the ipsilateral leg and contralateral arm muscles of control and SCI participants but only contralateral leg muscles of control participants. Interlimb reflexes evoked by superficial peroneal nerve stimulation were longer in latency and duration, and larger in magnitude in SCI participants. Interlimb reflex properties were similar for both SCI and control groups for radial nerve stimulation. Ascending interlimb reflexes tended to occur with a higher incidence in participants with SCI, while descending interlimb reflexes occurred with a higher incidence in able-bodied participants. However, the overall incidence of interlimb reflexes in SCI and neurologically intact participants was similar which suggests that the neural circuitry underlying these reflexes does not necessarily develop after central nervous system injury.     

Permanent alterations of spinal cord reflexes following nerve lesion in newborn rats

Sciatic nerve lesion in newborn rats is known to cause degeneration of a large number of axotomized motoneurones and spinal ganglion cells. Some of the surviving motoneurones exhibit abnormal firing properties and the projection pattern of central terminals of sensory neurones is altered. We report here on long-term changes in spinal cord reflexes in adult rats following neonatal nerve crush. In acutely spinalized and anaesthetized adult rats 4-6 months old in which the sciatic nerve had been crushed on one side at birth, the tibial nerve, common peroneal nerve or sural nerve were stimulated on the reinnervated and control side and reflex responses were recorded from the L5 ventral spinal roots. Ventral root responses (VRRs) to tibial and peroneal nerve stimulation on the side of the nerve lesion were significantly smaller in amplitude representing only about 15% of the mean amplitude of VRRs on the control side. The calculated central delay of the first, presumably monosynaptic component of the VRR potential was 1.6 ms on the control side while the earliest VRR wave on the side of the nerve lesion appeared after a mean central latency of 4.0 ms that seems too long to be of monosynaptic origin. These results suggest that neonatal sciatic nerve injury markedly alters the physiological properties and synaptic connectivity in spinal cord neurones and causes a marked depression of spinal cord responses to peripheral nerve stimulation.     

Distribution of the LPa3 and PPa3 neuronal processes in the pedal ganglia of the edible snail

By means of intracellular injection of the dye Lucifer yellow processes were revealed of the snail command neurones of escape behaviour LPa3 and RPa3 in pedal nerves ipsilateral to these neurones. A process of the neurone LPa3 was also found in the contralateral Nervus cutaneus pedalis secundus. Blockade of central chemical synapses by cadmium chloride did not lead to disappearance of motor reactions evoked by electrical stimulation of LPa3 and RPa3 neurones both on ipsi- and contralateral sides of the animal foot; this allowed to suggest a presence in the contralateral muscular pedal nerves of these neurones processes unrevealed by the used dyeing method.     

Hemispheric interaction in man during perception of visual stimuli]

Averaged evoked potentials (AEP) to verbal (letters) and nonverbal (random shapes) stimuli exposed in the left and right visual fields were registered in healthy subjects with normal vision. Analysis of the later AEP latencies pointed to asymmetry in the temporal parameters of the interhemispheric interaction. The late AEP latency is shorter in the right hemisphere than in the left hemisphere. The difference is more pronounced in responses to nonverbal stimuli. The earlier development of the evoked potential in the right hemisphere (or the later one in the left hemisphere) accounts for the interhemispheric difference in the temporal parameters of the late AEP components. Comparison of the latency of the component P300 to verbal and nonverbal stimuli presented in the ipsilateral or the contralateral visual fields reveals a transfer of the results of the cortical processing of visual information in the course of interhemispheric interaction.