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.     

Neuronal assemblies: single cortical neurons are obedient members of a huge orchestra

Spontaneous cortical activity of single neurons is often either dismissed as noise, or is regarded as carrying no functional significance and hence is ignored. Our findings suggest that such concepts should be revised. We explored the coherent population activity of neuronal assemblies in primary sensory area in the absence of a sensory input. Recent advances in real-time optical imaging based on voltage-sensitive dyes (VSDI) have facilitated exploration of population activity and its intimate relationship to the activity of individual cortical neurons. It has been shown by in vivo intracellular recordings that the dye signal measures the sum of the membrane potential changes in all the neuronal elements in the imaged area, emphasizing subthreshold synaptic potentials and dendritic action potentials in neuronal arborizations originating from neurons in all cortical layers whose dendrites reach the superficial cortical layers. Thus, the VSDI has allowed us to image the rather illusive activity in neuronal dendrites that cannot be readily explored by single unit recordings. Surprisingly, we found that the amplitude of this type of ongoing subthreshold activity is of the same order of magnitude as evoked activity. We also found that this ongoing activity exhibited high synchronization over many millimeters of cortex. We then investigated the influence of ongoing activity on the evoked response, and showed that the two interact strongly. Furthermore, we found that cortical states that were previously associated only with evoked activity can actually be observed also in the absence of stimulation, for example, the cortical representation of a given orientation may appear without any visual input. This demonstration suggests that ongoing activity may also play a major role in other cortical function by providing a neuronal substrate for the dependence of sensory information processing on context, behavior, memory and other aspects of cognitive function.     

Effect of motor deprivation in early ontogeny on evoked potentials of the sensomotor and visual cortex in the rat

The influence of long-term (3 months) locomotor deprivation of rats in a month age, on the evoked potentials (EP) of the sensorimotor and the visual cortex was studied in conditions of presentation of single and paired stimuli. Changes were revealed in both cortical zones. An increase of peak latency of the initial positive EP phase in the sensorimotor cortex, and prolongation of the process of changes in excitability of neural elements, elicited by conditioning stimulus, was revealed both in the sensorimotor and the visual areas. The effect of deprivation on the dynamics of changes in neuronal systems excitability was greater in the visual evoked responses.     

Differences in the corticofugal facilitating effect on evoked potentials in the neostriatum of rats and monkeys

Identical facilitation of the primary response to peripheral stimuli in rats and monkeys has been induced by local superficial cooling of the cortex in the somatosensory area S1. Higher facilitation of the evoked potentials was observed in the neostriatum of rats. Correlation of the evoked potentials with primary responses was more significant with respect to temporal than amplitude parameters. In monkeys, "cool" facilitation of the cortical primary response did not result in facilitation of the evoked potential in the neostriatum. Temporal correlation between the primary response and the evoked potential was less significant, whereas correlation in the amplitude was absent. The data obtained indicate the existence of differences in functional organization of corticofugal influences upon the neostriatum in rodents and primates.     

Laminar analysis of the origin of the various components of evoked potentials in slices of rat sensorimotor cortex

In slices of rat sensorimotor cortex, extracellular field potentials evoked by electrical stimulation of the white matter were recorded at various cortical depths. In order to determine the nature of the various components, experiments were performed in 3 situations: in a control perfusion medium, in a solution in which calcium ions have been replaced by magnesium ions to block synaptic transmission, and in cortices in which the pyramidal neurons of layer V had been previously induced to degenerate.In the control situation, the response at or near the surface was a positive-negative wave. From a depth of about 150 μm downwards, the evoked response consisted usually of 6 successive components, 3 positive-going, P11, P3 and P6 and 3 negative-going, N2, N4 and N5. P1 and N4 were apparent in superficial layers only. The amplitude of the remaining waves variable in the cortex but all diminished near the white matter.The early part of the surface positive wave arises from a non-synaptic activation of superficial elements, probably apical dendrites. The late part of the surface positive wave and the negative wave are due to the synaptic activation of neurons located probably in layer III.The large negative wave N2 represents principally the antidromic activation of cell bodies and possibly of proximal dendrites of neurons situated in layers III, IV and V, through the compound action potentials of afferent and efferent fibers may contribute to a reduced part to its generation.The late components N4 to P6 are post-synaptic responses. The negative component N5, the amplitude of which is largest in layers III and IV, represents excitatory responses of neurons located at various depths in the cortex. The nature of the positive component P6 is less clear, although the underlying mechanism might be inhibitory synaptic potentials.     

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.     

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.     

Comparative analysis of the role of the second and first somatosensory cortical areas in somatic responses of the medullary reticular formation in rats

Evoked potentials and unit activity in the medullary reticular formation were investigated in unanesthetized, curarized rats during cold blocking or after extirpation of the cortical representation of one of the stimulated limbs. Local cooling or extirpation in area SII, unlike blocking of area SI, leads to a small (up to 30%) decrease in amplitude and a very small change (up to 10 msec) in the temporal parameters of evoked potentials arising in the reticular formation in response to electrodermal stimulation of the contralateral limb, whose representation in the cortex was blocked. Predominance of corticofugal influences from SI over those from SII was discovered both in experiments with evoked potentials and during analysis of somatic spike responses of reticular formation neurons. Corticofugal control over activity of the medullary reticular formation in rats exerted by neuronal mechanisms of somatosensory areas SII and SI thus differs both qualitatively and quantitatively.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 15, No. 1, pp. 42–49, January–February, 1983.     

Distribution of neuropeptide Y immunoreactivity in human visual cortex and underlying white matter

Immunocytochemical techniques have been used to study neuropeptide Y (NPY) distribution in the human visual cortex (Brodman's areas 17, 18 and 19) NYP cell bodies belong mostly to inhibitory (multipolar and bitufted) but also to excitatory (bipolar and some pyramidal) neuronal types. Their distribution is similar in the three cortical areas studied: 20 to 40% of the NPY perikarya are located in the cortical gray matter, mostly in the deep layers, while the remaining 60 to 80% are located in the underlying white matter. Immunoreactive NPY processes form a rich network of intersecting fibers throughout the entire visual cortex. A superficial plexus (layers I and II) and a deep plexus (deep layer V and layer VI) of NPY fibers are present in areas 17, 18 and 19. In area 17, an additional well developed plexus is present in layers IVb and IVc. These plexuses receive branches from long parallel fibers arising from deep cortical layers or underlying white matter and terminating in superficial layers. Local or extrinsic NPY terminals wind around vessels in the cortex as well as in the white matter, and either penetrate them or form clusters of club endings on their walls. Our results suggest a role for NPY in human visual circuitry and in cortical blood flow regulation.     

A comparison of forepaw and vibrissae somatosensory cortical evoked potentials in the rat

Somatosensory evoked potentials were elicited in anesthetized rats by electrical stimulation of the forepaw (F-SEP) or the vibrissae (V-SEP) and were compared in order to study which of these is more valid animal model for studying the physiology and pathophysiology of somatosensory evoked potentials (SEPs) that are often recorded in man in a clinical setting. Intensity and rate functions were measured for the two potentials. The V-SEPs had larger amplitudes than the F-SEPs at high stimulus intensity and low stimulus rate. Furthermore, the ratios of the maximal amplitude of the F-SEP to that of the V-SEP (0.66) and of the areas under the curves of the two responses (0.75) reflected the smaller representation of the forepaw in the primary somatosensory cortex of the rat, compared to the vibrissae (ratio of cortical areas about 0.79). The differences should be taken into account when using median nerve SEP in the rat as a model of the human SEP. Study of V-SEPs in rat may provide insight into trigeminal nerve SEPs in man, which are also occasionally used for neurological evaluation.     

An analysis of the interaction of the parietal and visual regions of the cortex with the posterior lateral nucleus of the thalamus]

Cooling and ablation of the parietal associative (P) and primary visual projection (VI) areas in nembutalized cats revealed facilitating and inhibitory descending influences of the above areas on the postero-lateral nucleus (LP) of the ipsilateral thalamus where visual signals generate an early specific and a late unspecific components of heterogenous evoked responses. Unidirectional influences activating the early component and fully controlling the appearance and course of the late component are more manifest in P which is a part of the same associative brain system as LP; they are less manifest in VI which belongs to the projection system. At later cooling stages the centrifugal influences of P and VI are sometimes of opposite signs; this effect is connected with reciprocal relations between projection and association systems and processes or selfcontrol within the association system. The corticofugal effects also participate in the common activity of P and VI taking place to a certain degree at the level of the LP which activates these cortical structures.     

Cholinergic Pairing with Visual Activation Results in Long-Term Enhancement of Visual Evoked Potentials

Acetylcholine (ACh) contributes to learning processes by modulating cortical plasticity in terms of intensity of neuronal activity and selectivity properties of cortical neurons. However, it is not known if ACh induces long term effects within the primary visual cortex (V1) that could sustain visual learning mechanisms. In the present study we analyzed visual evoked potentials (VEPs) in V1 of rats during a 4–8 h period after coupling visual stimulation to an intracortical injection of ACh analog carbachol or stimulation of basal forebrain. To clarify the action of ACh on VEP activity in V1, we individually pre-injected muscarinic (scopolamine), nicotinic (mecamylamine), α7 (methyllycaconitine), and NMDA (CPP) receptor antagonists before carbachol infusion. Stimulation of the cholinergic system paired with visual stimulation significantly increased VEP amplitude (56%) during a 6 h period. Pre-treatment with scopolamine, mecamylamine and CPP completely abolished this long-term enhancement, while α7 inhibition induced an instant increase of VEP amplitude. This suggests a role of ACh in facilitating visual stimuli responsiveness through mechanisms comparable to LTP which involve nicotinic and muscarinic receptors with an interaction of NMDA transmission in the visual cortex.     

Analysis of the organization of afferent inputs in the projection cortex

Fast fluctuations in the evoked potentials (EP) at a local point of the projection cortex following stimulation of different pathways may reflect the activity of pyramidal neurons of different cortical layers. Analysis shows that the afferent and interarea projections to the somatic sensory cortex terminate on different neurons which can be regarded as relay neurons for a given pathway. Each group of neurons has its own system of inhibition for selective control of impulses coming along this pathway at the cortical level.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 368–372, July–August, 1970.     

Changes in Choline Acetyltransferase Activity and High-Affinity Choline Uptake,but Not in Acetylcholinesterase Activity and Muscarinic Cholinergic Receptors,in Rat Somatosensory Cortex after Sciatic Nerve Injury

Selected cholinergic markers (choline acetyltransferase, acetylcholinesterase, muscarinic acetylcholine receptor, high-affinity choline uptake) were studied in the hindlimb representation areas of the rat somatosensory cortex and within the visual cortex 1 to 63 days after unilateral transection of the sciatic nerve. In the contralateral somatosensory cortex, peripheral deafferentation resulted in a significant reduction of choline acetyltransferase activity (by 15%) 3 days after sciatic nerve injury, and in a significant reduction of high-affinity choline uptake (by 30%) 1 day after nerve transection, in comparison to untreated control rats. Investigations in individual cortical layers revealed that the decrease of both choline acetyltransferase activity and high-affinity choline uptake sites was mainly due to reductions in cortical layer V. Acetylcholinesterase activity and [³H]quinuclidinyl benzilate binding to muscarinic acetylcholine receptors were not affected by unilateral transection of the sciatic nerve. In the ipsilateral somatosensory cortex, as well as in the visual cortex at both cortical hemispheres, no significant changes in the cholinergic parameters studied could be detected. The data indicate that peripheral deafferentation of the somatosensory cortex results in a transient change of presynaptic cholinergic parameters within the affected somatosensory area as early as 1 to 3 days after the lesion; thus, they emphasize the involvement of cholinergic mechanisms in cortical reorganizational events.     

Changes in choline acetyltransferase activity and high-affinity choline uptake, but not in acetylcholinesterase activity and muscarinic cholinergic receptors, in rat somatosensory cortex after sciatic nerve injury

Selected cholinergic markers (choline acetyltransferase, acetylcholinesterase, muscarinic acetylcholine receptor, high-affinity choline uptake) were studied in the hindlimb representation areas of the rat somatosensory cortex and within the visual cortex 1 to 63 days after unilateral transection of the sciatic nerve. In the contralateral somatosensory cortex, peripheral deafferentation resulted in a significant reduction of choline acetyltransferase activity (by 15%) 3 days after sciatic nerve injury, and in a significant reduction of high-affinity choline uptake (by 30%) 1 day after nerve transection, in comparison to untreated control rats. Investigations in individual cortical layers revealed that the decrease of both choline acetyltransferase activity and high-affinity choline uptake sites was mainly due to reductions in cortical layer V. Acetylcholinesterase activity and [3H]quinuclidinyl benzilate binding to muscarinic acetylcholine receptors were not affected by unilateral transection of the sciatic nerve. In the ipsilateral somatosensory cortex, as well as in the visual cortex at both cortical hemispheres, no significant changes in the cholinergic parameters studied could be detected. The data indicate that peripheral deafferentation of the somatosensory cortex results in a transient change of presynaptic cholinergic parameters within the affected somatosensory area as early as 1 to 3 days after the lesion; thus, they emphasize the involvement of cholinergic mechanisms in cortical reorganizational events.     

Post-tetanic strengthening of evoked electrical responses of the sensomotor cortex]

A study has been made of the posttetanic potentiation of evoked potentials (PTP EP) in the sensorimotor cortex, appearing in response to VPL stimulation. A distinct PTP EP of the cortical surface has been found as well as considerable differences in its intensity recorded at different portions of deep cortical layers (700 to 1600 mu). Suggestions were made regarding the origin of the phenomena observed.     

Mechanisms of interaction between the parietal association and projection areas of the cat neocortex

Changes in evoked potentials in the first visual (VI), first somatic (SI), and parietal areas of the cortex during local cooling of each area were investigated under pentobarbital anesthesia. Two types of interaction were distinguished. Type I interaction was found in all areas in the early stages of local cooling and was reflected in a similar decrease in amplitude of evoked potentials in intact parts of the cortex. In the thalamic association nuclei — the pulvinar and posterolateral nucleus — somatic evoked potentials were unchanged but visual were transformed differently from those in the cortex. Type IIinteraction was found in the later stages of cooling and only between the association area and each of the projection areas. It was reflected in a greater change in amplitude of the evoked potentials and also in their configuration. In response to somatic stimulation in the early stage of type II interaction transformation of evoked potentials in the cortex took place sooner than in the nuclei; in the later stage it took place immediately after transformation of the "subcortical" evoked potentials. In response to photic stimulation transformations of cortical evoked potentials were always preceded by the corresponding transformations in the nuclei. It is suggested that type I interaction is formed by intercortical connections and type II by direct and subcortical relay connections. Differences in the role of the association area in interaction of types I and II when activated by stimuli of different modalities are discussed.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 573–581, November–December, 1978.     

Human cerebrocortical potentials evoked by stimulation of the dorsal nerve of the penis

Cortical evoked potentials resulting from stimulation of the dorsal nerve of the penis (DNP) provide a unique opportunity to document the cortical localization of sexual sensory representation in man. The DNP supplies sensory axons to the major portion of the human phallus, including the penile shaft and glans. Animal and human studies indicate that this nerve plays a crucial role in erection and ejaculation. Direct cortical evoked responses to DNP electrical stimulation were recorded in patients undergoing preoperative evaluation for resection of epileptic foci. These studies provided evidence that the primary sensory cortex contains a large area of cortex devoted to the afferent fibers of the DNP and that the sensory field is in a different location than previously described. The location and distribution of this response indicated the need for revision of the traditional concept of the sensory cortical homunculus.     

Recovery cycles of mass evoked potentials of different levels of the visual system following electrical stimulation of the optic nerve

Recovery cycles of mass evoked potentials of the optic tract, lateral geniculate body, optic radiation, and primary projection area of the visual cortex were investigated in amytal-anesthetized cats following electrical stimulation of the optic nerve (in some experiments, optic radiation) by paired short stimuli of supraliminal intensity. The recovery of the amplitude and time characteristics of all components of the mass responses to a testing stimulus applied to the nerve at different intervals after an identical conditioning stimulus was studied. The responses of all portions of the visual system (except the retina) were recorded simultaneously, which made it possible to compare the changes of their reactivity arising after the first stimulus under rigorously identical conditions. It was shown that at the upper levels of the visual system the exaltation phase of the recovery cycle and the depression phase following it become increasingly more pronounced and protracted. Depression is especially pronounced in the visual cortex, which maximally affects the recovery of the late components of the mass response. Under the experimental conditions the processes of successive inhibition in the cortex were more pronounced than at the lower levels. There are grounds to assume that the depression of the cortical responses is partially due to pre- and partially postsynaptic inhibition.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 251–259, May–June, 1970.     

Sensory projections to the cerebral cortex inPerodicticus potto edwarsi Bouvier

The cortical sensory projections of somatic, auditory, and visual origin have been mapped in the chloralosed potto. The pathways of the contralateral side of the body project in a classical somatotopic fashion to a large area SI, behind the motor cortex and the central sulcus. The latter constitutes the posterior boundary of the motor cortex only in its ventral part. In its middle zone the motor cortex extends to its posterior lip. Above the sulcus the motor zone is immediately adjacent to the preparietal area. Visual evoked potentials are recorded behind the transverse occipital sulcus with a maximal focus just caudal to an occipital dimple. The auditory area is situated between the sylvian and parallel sulci. No heterosensory potentials (visual or auditory) can be recorded from the somatomotor area, nor from any other part outside their primary projection area. An area of convergent somatic projection devoid of somatotopic organization is found between SI and the auditory zone and another one in front of the central sulcus. In view of the poor cortical heterosensory integration, the sensory projection system of the potto seems to be less developed than in the cat.