The tecto-thalamo-telencephalic system of the tortoise (electrophysiological investigation)

Using tortoises immobilized with diplacin to which chloralose had been added, or under chloralose — nembutal narcosis, we investigated the distribution of evoked potentials and neuronal responses in the thalamus and forebrain induced by electrical excitation of the optic tectum and by flashes of light. In the thalamus the main mass of cells that reacted to these stimuli was concentrated in the nucleus rotundus and the tecto-thalamic tract; in the forebrain it was concentrated in the general cortex, the pallial thickening, and the neostriatum. In the two latter structures responses with shorter latent periods than those in the general cortex predominated. Visual and tectal neuronal responses, especially those of convergent cells, displayed correlation in their latent periods and types of response, which was more clearly shown in the thalamus. Submaximal tetanization of the optic tectum had a facilitating effect on cortical responses produced by light flashes and excitation of the nucleus rotundus. Complete blocking of transmission of tectal impulsation to the forebrain was observed on destruction of the tecto-thalamic tract region bounded by the lateral bundle of the forebrain, the lateral geniculate body, and the nucleus rotundus. High-frequency excitation of the nucleus rotundus produced only partial blocking of transmission (of the late components). It is concluded that there are various pathways of tectal impulsation through the thalamus to the forebrain.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 296–306, May–June, 1970.     

Electrophysiological investigation of tecto-thalamo-telencephalic relations in frogs

Projections of the tectum mesencephali to the thalamus and telencephalon were investigated inRana temporaria. Individual cells in the optic neuropil of the lateral zone of the thalamus (corpus geniculatum thalami, n. Bellonci) and n. geniculatus lateralis respond to stimulation of the tectum mesencephali and to flashes but not to somatic stimuli. Many of the tectally reactive neurons in the medio-central zone of the thalamus, including n.postero-centralis, n.postero-lateralis, and n.rotundus, and in the telencephalon (the primordium of the hippocampus and septum) are convergent for somatic and visual impulses. The character of the macroresponses and spike responses to stimulation of the tectum mesencephali is the same for both zones of the thalamus. Tetanization within the lateral zone of the thalamus inhibits the conduction of visual and tectal impulses to the telencephalon, whereas during tetanization of the medio-central zone only the later components of visual and tectal evoked potentials of the telencephalon are suppressed. Responses with shorter latency than to stimulation of the medio-central zone arise in the telencephalon (primordium of the hippocampus) in response to electrical stimulation of the lateral zone by single pulses. In frogs the two divisions of the visual system — thalamo-telencephalic and tecto-thalamo-telencephalic — thus overlap considerably at the level of the thalamus and completely at the telencephalic level. In vertebrate phylogeny there is a progressive demarcation and specialization of these two visual channels.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 147–155, March–April, 1973.     

Comparative electrophysiological characteristics of afferent representation in the cortical and striatal divisions of the turtle forebrain

In experiments on immobilized, lightly anesthetized turtles the presence of visual and somatic representation was established in the subcortical striatal division of the forebrain — the pallial thickening, the dorsal ventricular ridge, and the putamen. In their physiological characteristics they are similar to the corresponding representation in the general cortex. The absence of significant differences between the latent periods of cortical and striatal evoked potentials to flashes and to stimulation of the dorsal thalamus indicates that visual projection fibers (from the lateral geniculate body) terminate at both cortical and striatal levels. Differences in the distribution of latent periods of unit responses in the cortex to visual and thalamic stimulation are due to the presence of a rotundo-telencephalic visual channel, with direct connections with the striatal and polysynaptic connections with the general cortex, as well as the geniculo-telencephalic tract. Considerable differences between the latent periods of the evoked potentials and also between unit responses to electrodermal stimulation in the cortical and striatal structures indicate that somatic projection fibers relay in the striatum on their path to the general cortex. Consequently, the somatosensory system of turtles is less corticalized than the visual system. Comparison of the results described with those obtained by workers studying other vertebrates suggests that the afferent supply of the striatum may be reorganized in the transition from premammals to mammals.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 7, No. 2, pp. 184–193, March–April, 1973.     

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     

Corticalization of two divisions of the visual system during vertebrate evolution

Data on the evolution of the visual system in vertebrate phylogeny are described. Visual projections are demonstrated in the telencephalon of cyclostomata (lampreys). The existence of a retino-thalamo-telencephalic pathway is demonstrated in elasmobranchs (skates). Two visual pathways are present in amphibians (frogs) and reptiles (turtles): retino-thalamo-telencephalic and retino-tecto-thalamo-telencephalic, and these overlap partly at the thalamic level in the lateral geniculate nucleus and completely in the telencephalon. In turtles the earliest visual and tectal impulses relay on their way to the telencephalon in the lateral geniculate body, and later impulses relay in the nucleus rotundus. In mammals (rats) visual tecto-cortical connections are seen; judging from the latent period of potentials arising in the visual cortex in response to stimulation of the superior colliculi these connections have one synaptic relay in the thalamus. The much shorter latent periods of visual evoked potentials recorded in the tectum of the monkey than in turtles (under identical chronic experimental conditions) confirm the views of morphologists on the progressive development of the tectal division of the visual system in vertebrate phylogeny. It is concluded that corticalization of both divisions of the visual system, i.e., the existence of telencephalic representation, appears in the early stages of vertebrate evolution.     

Electrophysiological analysis of cortico-tectal connections in the turtle

Two types of evoked potentials are recorded in the tectum mesencephali in response to electrical stimulation of the forebrain surface of the turtleEmys orbicularis. The results of a layer-by-layer analysis show that evoked potentials of type I in response to stimulation of the hippocampal and piriform cortex are generated outside the tectum. Evoked potentials of type II, consisting of two surface-negative components, are recorded in the tectum in response to stimulation of the rostro-central surface of the forebrain. The first component appeared after a latent period of 20 msec and lasted 40–60 msec; the second component appeared after 80–100 msec and lasted 100–300 msec. Layer-by-layer and pharmacological analysis showed that the first component of the type II evoked potential is generated in the tegmental structures of the mesencephalon, whereas the second (long-latency) is generated in the tectum. The tectal origin of the second component is confirmed by its interaction with the tectal response to photic stimulation or to electrical stimulation of the optic nerve, evidence that these evoked potentials are generated by common structures. The efferent pathway from the dorsal cortex to the primary visual center is unilateral and has features of polysynaptic projections (long latent period, low lability).     

Hypothalamic influences on unit activity in the cat superior colliculus

Experiments on immobilized unanesthetized cats showed that hypothalamic stimulation effectively modified spontaneous unit activity and activity evoked by photic stimulation in the superior colliculus. Long-latency responses, often with a tonic type of formation, were predominant. Meanwhile, definite differences were found in the character of influences from different regions of the hypothalamus. Stimulation of the anterior hypothalamic region and lateral hypothalamus led more frequently to inhibition of spontaneous activity, often expressed as the development of initial inhibition, especially during stimulation of the lateral hypothalamus. Definite modulation of spontaneous activity of cyclic type also developed. Influences from these structures on activity evoked by photic stimulation were chiefly facilitatory and modulating in character. Stimulation of the ventromedial nucleus could produce inhibitory and facilitatory effects equally on activity of tectal neurons, with a tendency for the frequency of manifestation of facilitation to increase when a series of stimuli was used. The mechanisms of triggering and realization of hypothalamic influences on activity in the superior colliculus are discussed.Ivano-Frankovsk State Medical Institute, Ministry of Health of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 560–568, November–December, 1979.     

Cortical distribution of photic evoked potentials

Short-latency evoked potentials (EPs) of the primary response (PR) type, recorded to flashes over wide areas outside the visual cortex, reflect the true arrival of visual impulses in these areas and are not the result of the passive spread of the EPs over the brain tissue. The EPs do not disappear after extirpation of the visual cortex in "nonvisual" areas of the neocortex. They continue to arise also after division of the internal capsule sparing its posterior third. EPs are no longer recorded after division of the posterior third of the internal capsule. It is concluded from these results that the spread of impulses evoked by photic stimulation, not only into the visual areas, but also into other areas of the posterolateral thalamic nuclei.S. M. Kirov Medical Institute, Gor'kii. Translated from Neirofiziologiya, Vol. 2, No. 5, pp. 482–487, September–October, 1970.     

Influence of the motor cortex on lateral geniculate responses evoked in the cat by contralateral superior colliculus stimulation

It is shown that in nembutal anesthetized cats, a single stimulation of motor cortex (MC) causes a response in lateral geniculate nucleus (LGN). The development of this response had a conditioning effect on the LGN response evoked by stimulation of the contralateral superior colliculus (SC), markedly inhibiting it. The degree of this inhibition depended on the time interval between the cortical conditioning stimulation and the tectal test stimulation. A single conditioning MC stimulation did not noticeably change the LGN responses evoked by a light stimulus, but markedly inhibited visual responses from deep SC layers (those regions which on stimulation gave rise to LGN responses). From the results, it is suggested that the MC monitors the execution of tectal influences on LGN function at the tectal level rather than the geniculate level, and it is precisely by this means that it regulates saccadic suppression of LGN function, in the realization of which, as presumed earlier, the SC takes part.A. I. Karaev Institute of Physiology, Azerbaijan Academy of Sciences, Baku. Translated from Neirofiziologiya, Vol. 24, No. 4, July–August 1992.     

Nonolfactory afferent telencephalic projections in frogs

The degree of modal specificity of neurons of the tectum, dorsal thalamus, and primordial hippocampus relative to visual (photic) and somatic (tactile) stimulation was investigated in experiments on frogs (Rana temporaria) immobilized with tubocurarine. The specificity of sensory information arriving at the successive levels of the frog's thalamo-telencephalic afferent system diminishes in an ascending direction. Evoked potentials arising in the telencephalon in response to electrical stimulation of the sciatic nerve and to flashes are found not only in the primordial hippocampus, but also bilaterally in the septum and striatum. It is concluded on the basis of discharges recorded in the fibers of the thalamo-telencephalic tracts during somatic and visual stimulation that fibers carrying nonolfactory information into the telencephalon run in the medial and lateral forebrain bundles.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. International Brain Research Laboratory, Kotor, Yugoslavia. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 537–544, September–October, 1973.     

Tecto-thalamo-telencephalic interrelationships following visual deafferentation

21-23 months after uni- and bilateral enucleation of the eyes, the turtles Emys orbicularis and Testudo horsfieldi exhibited atrophy, gliosis and residual degenerative changes in the visual nerves and tracts and in the two upper layers of the optic tectum, as well as a reduced density of fibres in the tecto-thalamic tract on the deafferentated side. Electrophysiological experiments on the turtles have shown that tectal impulses en route to the general cortex of the forebrain are relayed in the n. rotundus. Conduction of impulses along the tecto-geniculo-cortical path, found in intact animals, ceases, which is apparently due to transsynaptic changes in the surface layers of the optic tectum.     

Tegmento-telencephalic relations in turtles

Electrophysiological characteristics of tegmental projections in the forebrain were studied in immobilized turtles (Emys orbicularis), anesthetized with chloralose. The main zone of representation of the tegmentum is located in the striatum, where evoked responses with shorter latencies were recorded and a larger number of units responding distinctly to tegmental stimulation was concentrated than in the dorsal ventricular ridge and general cortex. At the striatal level predominance of lateral tegmental projections was found in the lateral zone and of medial tegmental projections in the medial zone of the striatum. An inhibitory action of conditioning stimulation of the tegmentum on somatic evoked potentials and single unit responses was established. An attempt was made to compare the tegmento-telencephalic system in reptiles and mammals.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 255–263, May–June, 1980.     

Unit responses of the cat caudate nucleus to cortical stimulation before and after destruction of nonspecific thalamic nuclei

Responses of caudate neurons to stimulation of the anterior sigmoid and various parts of the suprasylvian gyrus were studied in acute experiments on cats. The experiments consisted of two series: on animals with an intact thalamus and on animals after preliminary destruction of the nonspecific thalamic nuclei. Stimulation of all cortical areas tested in intact animals evoked complex multicomponent responses in caudate neurons with (or without) initial excitation, followed by a phase of inhibition and late activation. The latent periods of the initial responses to stimulation of all parts of the cortex were long and averaged 14.5–25.5 msec. Quantitative and qualitative differences were established in responses of the caudate neurons to stimulation of different parts of the cortex. Considerable convergence of cortical influences on neurons of the caudate nucleus was found. After destruction of the nonspecific thalamic nuclei all components of the complex response of the caudate neurons to cortical stimulation were preserved, and only the time course of late activation was modified.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 464–471, September–October, 1980.     

Tegmento-thalamic relations in turtles

A focus of evoked potentials and the largest number of spike responses of single units to tegmental stimulation were found in immobilized turtles (Emys orbicularis), lightly anesthetized with chloralose, in the ventral region of the thalamus, which is a heterosensory zone of predominantly somatosensory modality. Incomplete separation of lateral- and medial-tegmental projections between the dorsal and ventral portions of the ventral thalamic region respectively was discovered. Tegmental stimulation, coinciding with or preceding electrodermal or photic stimulation, causes predominant depression of somatic single unit responses, but has less effect on visual responses. The possibility of comparison of tegmento-thalamic systems in reptiles and mammals is discussed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 165–174, March–April, 1980.     

Effect of background illumination on evoked potentials of the visual system in the turtle

We discovered an enhancing effect of background illumination on amplitude and total duration of electrical reactions of the tectum of the midbrain and pallial thickening in response to a flash and electrical stimulation of the optic nerve. This effect is analogous to the phenomenon of photic potentiation known for the visual system of mammals. Changes of evoked potentials in the contralateral pallial thickening and tectum were fairly stable and survived throughout the course of the entire period of illumination (up to 30 min). The effect was intensified with an increase of illumination intensity. Intensification of response on the part of the tectum and pallial thickening during steady illumination was accompanied by a weakening of slow background electrical activity. During the action of background illumination, the excitability of the tectum rose considerably with direct electrical stimulation. The influence of prolonged illumination on responses of the tectum and pallial thickening was more clearly detected at submaximal strengths of stimulation of the optic nerve or tectum. All of the effects of photic potentiation are confined to centers contralateral to the illuminated eye. This indicates the absence of diffuse effects on excitability of the turtle brain.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 219–224, September–October, 1969.     

Electrophysiological analysis of representation of the somatosensory system in the tectum opticum of the dogfish

Evoked potentials to electrical stimulation of the spinal cord, its dorsal roots and the superficial orbital branch of the facial nerve were recorded in the tectum opticum of the Black Sea piked dogfishSqualus acanthias L. The distribution of evoked potentials over the surface and in the depth of the tectal lamina and also dependence of the parameters of the responses on the strength and frequency of the stimuli and intervals between them in the case of paired stimulation were studied. Evoked potentials were shown to be tectal in origin, to be recorded mainly contralaterally, and to exhibit specific dynamics of changes in response components under the influence of the various procedures and specific dependence of the responses on the location of the recording point. Significant differences were found between the characteristics of evoked potentials generated in superficial and deep layers of the tectum opticum. The nature and physiological role of nonvisual projections to this structure and also its role in the integrative function of the ichthyopsid brain are discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 182–191, March–April, 1980.     

Electrical activity of thalamocortical association systems in postnatal ontogeny of the cat

Electrical responses to somatic, photic, and acoustic stimulation in the sensomotor, parietal, temporal, and occipital regions of the cortex were studied in the nucleus lateralis posterior and nucleus ventralis lateralis of the thalamus by recording averaged evoked potentials in kittens (aged 3 to 41 days) anesthetized with pentobarbital. A definite order of maturation of afferent inputs into cortical association areas was demonstrated. The parietal cortex was shown to become polysensory before the sensorimotor cortex. It is suggested that the nucleus lateralis posterior is the main thalamic nucleus responsible for conduction of visual information to the cortex in kittens during the first month of life. Incorporation of this nucleus into the system conducting somatic impulsation to the sensorimotor cortex takes place by the age of 3 weeks.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 476–482, September–October, 1982.     

Evoked potentials to electrical stimulation of the facial nerve in the carp tectum mesencephali

Tectal evoked potentials to stimulation of the facial nerve, containing afferent fibers of nonolfactory chemoreception, in the carp are positive evoked potentials with a latent period of 5 to 25 msec which show no phase shift as the microelectrode is advanced to a depth of 600 µ. Depending on the amplitude and latency of evoked potentials seven active zones differing in one or both parameters were distinguished in the ipsilateral tectum mesencephali. The role of impulses from the medulla in the mechanism of tectal evoked potentials to facial nerve stimulation is proved by differences in latent periods and disappearance of the tectal response (although it is preserved in the primary center) after severance of connections between the two parts of the brain. Descending influences from the tectum on the primary center were found: its extirpation disturbs evoked potential generation in several parts of the medullla, so that they either disappear completely or their parameters are modified.A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 39–46, January–February, 1976.     

Multisensory convergence on neurons of the motor cortex in unanesthetized cats

Postsynaptic potentials (PSPs) of 83 neurons in the motor cortex of unanesthetized cats in response to electrodermal, photic, and acoustic stimulation were investigated by intra-and quasi-intracellular recording methods. Most cells responded to stimulation of at least one limb. About 60% of neurons of the posterior and over 75% of neurons of the anterior sigmoid gyrus responded to stimulation of two (or more) limbs. In 29 of 39 neurons of the anterior and 12 of 44 of the posterior sigmoid gyrus PSPs with a short (less than 50 msec) and stable latent period were evoked by flashes and clicks. On presentation of two somesthetic stimuli complete blocking (if the interval was less than 30–60 msec) or weakening (interval 30–200 msec) of responses to the second (testing) stimulus was observed. On presentation of paired photic (or acoustic) stimuli or paired stimuli of different modalities at various intervals from 0 to 100 msec, the testing response was often potentiated. The character of the responses and their interaction thus differed from those obtained under chloralose anesthesia [6, 7]. It is postulated that under the action of chloralose a system of neurons with strong excitatory feedback is formed in the motor cortex which may respond to stimuli of different modalities by something resembling the "all or nothing" principle.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 563–573, November–December, 1971.     

Projections of the optic tectum and the mesencephalic nucleus of the trigeminal nerve in the tegu lizard (Tupinambis nigropunctatus)

Summary Fibers undergoing Wallerian degeneration following tectal lesions were demonstrated with the Nauta and Fink-Heimer methods and traced to their termination. Four of the five distinct fiber paths originating in the optic tectum appear related to vision, while one is related to the mesencephalic nucleus of the trigeminus. The latter component of the tectal efferents distributes fibers to 1) the main sensory nucleus of the trigeminus, 2) the motor nucleus of the trigeminus, 3) the nucleus of tractus solitarius, and 4) the intermediate gray of the cervical spinal cord.The principal ascending bundle projects to the nucleus rotundus, three components of the ventral geniculate nucleus and the nucleus ventromedialis anterior ipsilaterally, before it crosses in the supraoptic commissure and terminates in the contralateral nucleus rotundus, ventral geniculate nucleus and a hitherto unnamed region dorsal to the nucleus of the posterior accessory optic tract.Fibers leaving the tectum dorso-medially terminate in the posterodorsal nucleus ipsilaterally and the stratum griseum periventriculare of the contralateral tectum. The descending fiber paths terminate in medial reticular cell groups and the rostral spinal cord contralaterally and in the torus and the lateral reticular regions ipsilaterally. The ipsilateral fascicle also issues fibers to the magnocellular nucleus isthmi.