Ascending Activating System Research Articles

Engine Of Consciousness In Brain - A Review

Consciousness is the cognitive faculty which is evolved by natural selection and it has designed a sense of ourselves and our surroundings. The cerebral cortex is ‘the seat of consciousness’ in humans and mammals. The salient features of consciousness, they are human consciousness exists, involves short term memory, it occurs independently of sensory inputs, it displays steerable attentions, has capacity for attentive interpretations of complex or ambiguous data, consciousness disappears in a deep sleep and finally, it the contents of several basic modalities within a single unified experience. The consciousness depends on the ascending projections from the dorsal that form the ascending activating system. The engine of consciousness depends mainly on the brain's activity of sustaining rich dynamics in neural activity. The aim of the present review is to study the aspects of consciousness and thereby, the present scope of retrieving people out of consciousness and to consciousness disorders. This research was conceived as a scoping literature review. This review has accessed existing reviews and researches in the last decade mostly, through PMC database, MeSH, Google Scholar, , , CrossRef. Considered research was limited to manuscripts related consciousness, drugs relations, and Alzheimer's disease. This review excluded researches, other neurological disorders not related to consciousness, physiological impairment of consciousness. Quality of articles used was assessed using Quality assessment tools and graded as strong, moderate and weak. The description of the included studies for the review is tabulated.

Cholinergic basal forebrain structures are not essential for mediation of the arousing action of glutamate.

The cholinergic basal forebrain contributes to cortical activation and receives rich innervations from the ascending activating system. It is involved in the mediation of the arousing actions of noradrenaline and histamine. Glutamatergic stimulation in the basal forebrain results in cortical acetylcholine release and suppression of sleep. However, it is not known to what extent the cholinergic versus non-cholinergic basal forebrain projection neurones contribute to the arousing action of glutamate. To clarify this question, we administered N-methyl-D-aspartate (NMDA), a glutamate agonist, into the basal forebrain in intact rats and after destruction of the cholinergic cells in the basal forebrain with 192 immunoglobulin (Ig)G-saporin. In eight Han-Wistar rats with implanted electroencephalogram/electromyogram (EEG/EMG) electrodes and guide cannulas for microdialysis probes, 0.23μg 192 IgG-saporin was administered into the basal forebrain, while the eight control animals received artificial cerebrospinal fluid. Two weeks later, a microdialysis probe targeted into the basal forebrain was perfused with cerebrospinal fluid on the baseline day and for 3h with 0.3mmNMDA on the subsequent day. Sleep-wake activity was recorded for 24h on both days. NMDA exhibited a robust arousing effect in both the intact and the lesioned rats. Wakefulness was increased and both non-REM and REM sleep were decreased significantly during the 3-h NMDA perfusion. Destruction of the basal forebrain cholinergic neurones did not abolish the wake-enhancing action of NMDA. Thus, the cholinergic basal forebrain structures are not essential for the mediation of the arousing action of glutamate.

Short-Term Effects of Chewing on Task Performance and Task-Induced Mydriasis: Trigeminal Influence on the Arousal Systems.

Trigeminal input to the ascending activating system is important for the maintenance of arousal and may affect the discharge of the noradrenergic neurons of the locus coeruleus (LC), whose activity influences both vigilance state and pupil size, inducing mydriasis. For this reason, pupil size evaluation is now considered an indicator of LC activity. Since mastication activates trigeminal afferent neurons, the aims of the present study, conducted on healthy adult participants, were to investigate whether chewing a bolus of different hardness may: (1) differentially affect the performance on a cognitive task (consisting in the retrieval of specific target numbers within numerical matrices) and (2) increase the dilatation of the pupil (mydriasis) induced by a haptic task, suggesting a change in LC activation. Results show that chewing significantly increased both the velocity of number retrieval (without affecting the number of errors) and the mydriasis associated with the haptic task, whereas simple task repetition did not modify either retrieval or mydriasis. Handgrip exercise, instead, significantly decreased both parameters. Effects were significantly stronger and longer lasting when subjects chewed hard pellets. Finally, chewing-induced improvements in performance and changes in mydriasis were positively correlated, which suggests that trigeminal signals enhanced by chewing may boost the cognitive performance by increasing LC activity.

Activity Profiles of Cholinergic and Intermingled GABAergic and Putative Glutamatergic Neurons in the Pontomesencephalic Tegmentum of Urethane-Anesthetized Rats

Cholinergic neurons in the pontomesencephalic tegmentum form part of the ascending activating system and are thought to participate in stimulating cortical activation. Yet in the laterodorsal tegmental and pedunculopontine tegmental nuclei (LDT and PPT), they lie intermingled with GABAergic and glutamatergic neurons, which could also modulate cortical activity and sleep-wake state. To characterize the discharge of these cell types in relation to cortical activity, we recorded neurons in urethane-anesthetized rats during spontaneous slow wave and somatosensory evoked fast electroencephalographic (EEG) activity, then labeled the cells by juxtacellular technique with Neurobiotin (Nb) and dual-immunostained them for vesicular acetylcholine transporter (VAChT) and glutamic acid decarboxylase (GAD). All cholinergic cells discharged minimally during prestimulation (approximately 0.5 Hz) and moderately in a tonic manner (approximately 4 Hz) during stimulation. Being heterogeneous, some GABAergic, called "On," cells (approximately 48%) increased their discharge (from approximately 4 to 7 Hz), whereas others, called "Off" cells (approximately 38%), decreased or ceased firing during stimulation. Similarly, some noncholinergic/non-GABAergic On cells increased (from approximately 2 to 6 Hz, approximately 49%), whereas other Off cells decreased firing ( approximately 35%) during stimulation. Putative glutamatergic On together with GABAergic On neurons could thus act in parallel with cholinergic cells to stimulate cortical activation. Possibly influenced by cholinergic On and glutamatergic Off cells, whose change in discharge precedes theirs, the GABAergic Off cells could oppose neighboring neurons such as noradrenergic cells, which discharge during waking and cease firing during sleep. By concerted activity, these heterogeneous cell groups can modulate cortical activity and behavioral state across the sleep-waking cycle.

A Glycinergic input into the intralaminar thalamic nuclei

Event Abstract Back to Event A Glycinergic input into the intralaminar thalamic nuclei Kristof Giber1*, Viktor Plattner1, Hajnalka Bokor1 and Laszlo Acsady1 1 Dept. Cellular and Network Neurobiology , Institute of Experimental Medicine, Hungary In humans intralaminar thalamus is critical to maintain normal conscious states. Recently these nuclei were shown to receive a selective and dense glycinergic input in transgenic mice expressing EGFP linked to the glycine-transporter-2 protein (GlyT2). The aims of the present study were to determine the origin of the Glyt2-positive thalamic fibers, to characterize the morphology and co-transmitter of the glycinergic axon terminals and to examine the firing properties of the projecting neurons in vivo. Following the injections of retrograde tracer fluorogold into the intralaminar thalamus, the largest proportion (51.5%) of the labeled glycinergic neurons were localized within the the ipsilateral oral and caudal pontine nuclei (PnO-PnC). Sixty-one percent of the projecting cells in this region were EGFP-positive, whereas most contralateral neurons were GlyT2-negative. Injections of anterograde tracer Phaseolus vulgaris leucoagglutine into the PnO-PnC resulted in a dense labeling of large terminals in the ipsilateral intralaminar nuclei. Out of these terminals, 48.9% were EGFP-positive, while this ratio was only 9.6% in the contralateral hemisphere. The GlyT2-positive boutons were GABA-immunopositive and established multiple synapses on the proximal dendrites of relay cells. Juxtacellular recording of a GlyT2-positive PnO cell projecting to the thalamus disclosed a firing pattern consisting of rhythmic clusters of spikes at 40-50Hz in synchrony with the EEG upstates. We demonstrated that beside the well-known excitatory ascending activating system a novel inhibitory pathway reaches the thalamus from the brainstem. The glycine- and GABAergic ponto-thalamic pathway raises the question how an inhibitory arousal system modulates the thalamic activity and the conscious states. Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Developmental neurobiology and subcortical functions Citation: Giber K, Plattner V, Bokor H and Acsady L (2009). A Glycinergic input into the intralaminar thalamic nuclei. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.056 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Feb 2009; Published Online: 27 Feb 2009. * Correspondence: Kristof Giber, Dept. Cellular and Network Neurobiology , Institute of Experimental Medicine, Budapest, Hungary, giber@koki.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Kristof Giber Viktor Plattner Hajnalka Bokor Laszlo Acsady Google Kristof Giber Viktor Plattner Hajnalka Bokor Laszlo Acsady Google Scholar Kristof Giber Viktor Plattner Hajnalka Bokor Laszlo Acsady PubMed Kristof Giber Viktor Plattner Hajnalka Bokor Laszlo Acsady Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Afferent connections of septal nuclei of the domestic chick (Gallus domesticus): A retrograde pathway tracing study

The afferents to the septum of the domestic chicken were studied using retrograde tracers, rhodamine conjugated latex bead or Fast Blue, placed in different septal subregions. The results were verified by anterograde tracer injections deposited to selected areas. The main telencephalic afferents to the septum arise ipsilaterally from the hippocampal formation, dorsolateral corticoid area, piriform cortex, amygdaloid pallium, and the ventral pallidum. Contralateral afferents originate from the lateral septum and the amygdaloid pallium. A massive bilateral projection arises from the lateral hypothalamus. Other hypothalamic afferents arise from the periventricular, paraventricular and anterior medial nuclei, and the premammillary and mammillary areas. The dorsal thalamic nuclei (dorsal medial anterior and posterior) and the reticular dorsal nuclei also contribute septal afferents. Brainstem afferents arise bilaterally from the ventral tegmental area, substantia nigra, central gray, A8, locus coeruleus, ventral subcoeruleus nucleus, and raphe nuclei. The main terminal fields for septal afferents lie in the lateral septal nucleus and the belt of medial septal nucleus. The core of the latter is invaded mainly by fibers from the brainstem, presumably belonging to the ascending activating system. The septal afferents of the chicken are largely similar to those of other avian and nonavian species. The most prominent differences with previous pigeon data were found in the subregional selectivity of the hippocampal formation, dorsolateral corticoid area, mammillary nuclei, some dorsal thalamic nuclei, substantia nigra, and subcoeruleus nuclei in their projections to defined septal nuclei.

Perioperative EEG monitoring: studies of the electrophysiological arousal mechanism

Electroencephalogram recordings have been advocated for assessment of changes in cerebral function during anaesthesia. Controversy exists on the specificity of EEG parameters indicating depth of anaesthesia, because cortical electrical activity is modulated not only by drugs but also by a variety of exogenous and endogenous stimuli. In clinical practice, EEG measures often fail to accurately predict anaesthetic depth since the effects of nociceptive stimulation on the EEG are still not well defined. Previous reports indicate that in anaesthetised patients sensory stimulation may induce a shift to a dominant EEG frequency with faster waves similar to patterns seen during emergence from anaesthesia under certain circumstances. This electrophysiological arousal (EEG desynchronisation) may be associated with clinical arousal phenomena such as movement and increases in haemodynamic and respiratory activity. However, the mechanism of arousal during emergence from anaesthesia may be quite different from arousal reactions induced by noxious stimulation. Recent studies indicate that surgical stimulation can induce increases in slow wave EEG-activity ("reverse" or "paradoxical" arousal) associated with clinical arousal phenomena. Stimulus related delta patterns also were observed after acoustical or painful stimulation in head injured patients. The occurrence of slow EEG wave patterns may be related to functional blockade of the ascending activating system of the brain stem. In contrast, slowing of the EEG is comparable to EEG changes seen with increasing concentrations of anaesthetics. This indicates the difficulty to discriminate arousal phenomena from drug effects using EEG monitoring alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomical organization of the telencephalic connections of the parafascicular nucleus in adult and developing rats

The parafascicular nucleus (PFN) of the rat, homologous to the human centre médian, is an intralaminar nucleus of the thalamus, classically considered as part of the ascending activating system. We have previously demonstrated that it is also connected to several subcortical nuclei. To obtain a more detailed picture of the connectivity of the PFN, the organization and the topography of the reciprocal parafascicular-telencephalic relationships were studied in both adult and developing rats, using anterograde and retrograde neuronal tracers. In the adult rat, the ascending parafascicular projections were densest to the striatum, dense to the frontal and least dense to cingulate cortex, and were strictly ipsilateral. They displayed a loose topography, with the more medial parafascicular neurons projecting to the medial frontal and cingulate cortex and medial striatum, and the more lateral neurons projecting to the lateral frontal cortex and lateral striatum. All these connections were already present at embryonic day 19. Parafascicular neurons projecting to the telencephalon in adult rats were mostly of the multipolar type, with a few bipolar neurons. In neonatal rats they showed a bipolar morphology at birth; they became mostly multipolar later on, with an increasing complexity of the dendritic arbor up to postnatal day 10. Neurons in the frontal cortex retrogradely labelled from the PFN were more numerous perinatally, and decreased as early as postnatal day 5. The telencephalic connections of the PFN were found to be more discrete and restricted than previously thought, thus suggesting a more specific functional role for the nucleus than cortical recruitment.

The visceral sector of the thalamic reticular nucleus in the rat

Visceral sensory perception is subjected to modulation by attention or distraction, like other sensory systems. The thalamic reticular nucleus is a key region in selective attention, effecting a change in the mode of thalamocortical transmission. Each major thalamocortical system is connected with a particular sector of the thalamic reticular nucleus. No connections from the thalamic reticular nucleus have been described to the visceral sensory thalamus. We used axonal tracing techniques to study the possible existence of reciprocal connections between the visceral sensory relay in the lateral ventroposterior parvicellular thalamic nucleus, and the reticular nucleus of the thalamus. We also studied the projections from the visceral sensory cortex, located in the granular insular cortex in the rat, to the reticular nucleus of the thalamus. We found a convergent input from both thalamic and cortical sensory visceral regions to the same sector of the reticular nucleus of the thalamus. This visceral sector in turn sent GABAergic feedback connections to the lateral ventroposterior parvicellular thalamic nucleus. In addition, the visceral thalamus received histaminergic projections from the tuberomammillary nucleus, and noradrenergic projections from the locus coeruleus; both nuclei belong to the ascending activating system. Our findings indicate that the visceral sensory thalamocortical pathway is connected to the same subcortical structures that provide attention mechanisms for other thalamocortical systems.

Brainstem activates paroxysmal discharge in human generalized epilepsy

In nine patients with generalized epilepsy of convulsive seizures, the excitability change of the brainstem was evaluated over the course of the interictal paroxysmal discharge (poly spike-and-wave complex, poly SWC). The evaluation was carried out by a sequential analysis of brainstem auditory evoked potentials (BAEPs) before and during one sequence of poly SWC. The characteristics of BAEPs, i.e. far-field evoked potentials, allowed the evaluation of the excitability change in the brainstem, which was not influenced by the cortical activity. The excitability in the ventral brainstem, measured with the parameters of wave-III, showed a biphasic fluctuation (deceleration–acceleration) before the onset of poly SWC (minima at −0.7±0.4 s). On the other hand, the excitability in the dorsal brainstem, measured with the parameters of wave-V, showed no significant difference over the course of poly SWC. The results suggest that the biphasic excitability change in the ventral brainstem is conveyed to the cortex through the ascending activating system. The excitability acceleration preceded by deceleration in the ventral brainstem probably synchronizes the cortical activity profoundly enough to produce poly SWC through the activation of intralaminar thalamic neurons.

Negative correlation of reaction times and the auditory P50 in a Go, No-Go paradigm.

We investigated the relationship between reaction times in a Go, No-Go paradigm and various components of the auditory event-related potentials. The P50 latencies in the Go trials were significantly earlier than those in the No-Go trials. The N200 and P300 were positively associated with the reaction times. However, the P50 latencies showed negative correlation with the reaction times, and the negative correlation at F3 was the largest. Referring to source studies on P50, it is suggested that the activation of either the ascending activating system or the left premotor area through that system might affect the speed of reaction.

5-HT-like immunoreactivity in the brains of plethodontid and salamandrid salamanders (Hydromantes italicus, Hydromantes genei, Plethodon jordani, Desmognathus ochrophaeus, Pleurodeles waltl): an immunohistochemical and biocytin double-labelling study.

The distribution of 5-HT-like-immunoreactive cell bodies and fibres was studied in the brains of the salamanders Hydromantes italicus, H. genei, Plethodon jordani, Desmognathus ochrophaeus (family Plethodontidae), and Pleurodeles waltl (family Salamandridae). In addition, double-labelling experiments with biocytin were carried out to identify the relationship between serotonergic fibres and neurons involved in the processing of sensory and sensorimotor information. In all species, 5-HT-immunopositive somata are found in the ventral thalamus close to the ventricle forming the paraventricular organ. In the hypothalamus, cells are labelled in the ependymal layer around the infundibular recess and at the lateral edge of the periventricular grey. In the pretectum, a few immunoreactive cells are situated dorsolaterally in the grey matter. In the tegmentum and medulla oblongata, cells of the raphe nuclei are regularly distributed along the midline; labelled perikarya are occasionally found in the cervical spinal cord. 5-HT-like-immunoreactive fibres are widely distributed throughout the nervous system. Densely arborizing fibres are found in the olfactory bulb, striatum and amygdala. Distinct fibre projections extend in the ventral thalamus and tectum. Biocytin tracing of striatal and tectal projection neurons and ascending reticular neurons combined with the demonstration of 5-HT suggest that the striatum, the tectum and the ascending activating system are strongly influenced by 5-HT.

Differential cerebrovascular and metabolic responses in specific neural systems elicited from the centromedian-parafascicular complex

The effect of electrical stimulation of the centromedian-parafascicular complex on local cerebral blood flow and local cerebral glucose utilization was investigated in anesthetized, paralysed and ventilated rats. Local cerebral blood flow and local cerebral glucose utilization were measured in separate groups of animals using the autoradiographic ( 14C)iodoantipyrine and ( 14C)2-deoxyglucose methods, respectively. Because of the well-established centromedian-parafascicular complex neuroanatomical connections, three functional neuronal systems were analysed and compared: the extrapyramidal motor system the limbic system and the reticular formation, also known as the ascending activating system. Cortical regions not included in the limbic system were considered separately. The validity of comparisons between changes in local cerebral blood flow and local cerebral glucose utilization across the brain was verified by assessing the reactivity and stability of the cortical blood flow during long-term centromedian-parafascicular complex stimulation. Centromedian-parafascicular complex stimulation elicited a marked but heterogeneous increase in local cerebral blood flow in 50 of the 52 cerebral structures measured. The most pronounced increases were seen in the lateral habenular nucleus (331 ± 30% of control), the zona incerta (400 ± 55%), the mesencephalic reticular formation (415 ± 122%) and the parietal cortex (211 ±35%). In contrast, local cerebral glucose utilization remained statistically unchanged (P$˛0.05) in 28 of these 50 individual brain regions during centromedian-parafascicular complex stimulation. The most pronounced increases in local cerebral glucose utilization were seen in the zona incerta (123 ±28%) and the mesencephalic reticular formation (193 ±26%). Local cerebral blood flow and local cerebral glucose utilization were linearly related in unstimulated controls, considering either all brain regions taken as a whole or the three systems separately. The significant increase in the slopes of the regression line between local cerebral blood flow and local cerebral glucose utilization for the reticular formation and the limbic system during centromedian-parafascicular complex stimulation indicates, however, that the coupling mechanisms for these systems, but not for the extrapyramidal motor system, were reset. The local cerebral blood flow to local cerebral glucose utilization ratio was heterogeneous in controls and differentially increased during centromedian-parafascicular complex stimulation, being markedly pronounced in the parietal cortex and in the reticular formation. We conclude that these results, for the first time, provide evidence that, the functionally well-defined neural networks may have different mechanisms whereby changes in vascular and metabolic demands are regulated.

Vascular Dementia

Vascular dementia is almost always associated with organic brain lesions due to ischemia, not with arteriosclerosis alone. In Japan, more than 50% of dementia in population older than 65 years are of vascular origin. Vascular dementia occurs with diffuse vascular lesions in the cerebral white matter or circumscribed lesions in particular areas such as the thalamus, anterior limb of the internal capsule, and cingulate gyrus, all of which constitute the ascending activating system or the limbic system. Vascular dementia is clinically characterized by stepwise progression, fluctuating course and predominant deterioration of intelligence with relative preservation of personality. Reversibility, disproportionate impairment of intelligence and personality, and dementia caused by a focal lesion observed in vascular dementia pose problems with regard to the classical concept of dementia. The similarity and difference between remitting dementia and disturbance of consciousness remain to be scrutinized.

Impairment of neuropsychological functions in children with medulloblastomas and astrocytomas in the posterior fossa.

Neuropsychological impairment after removal of posterior fossa tumors is a recurrent issue in child neuropsychology and neurosurgery. The aim of this study was to assess verbal and performance intelligence, as well as immediate and sustained attention, in children with medulloblastoma or astrocytoma operated on for total removal of the lesion. Surgical treatment of medulloblastoma was always followed by chemoradiotherapy. Siblings of both tumor groups (without a history of neurological disease, even suspected) were examined as controls. The results were as follows: the cognitive performances were significantly poorer than the controls in both groups; the children with medulloblastoma scored below normal. Attention deficits were present in both groups as well when the usual clinical tests were used. When assessed by means of computerized methodology, the same function was normal. Considering that both groups of children underwent the same surgical treatment and all had hydrocephalus, the severe intellectual impairment reported only in patients with medulloblastoma can be ascribed to chemoradiotherapy. In contrast, the attention deficits present in both groups could be ascribed to the proximity of lesions to the ascending activating system. Malfunctioning of the activating system seems to be bypassed by the computerized administration of stimuli, which supplies motivation and kindles attention.

Effect of atropine on intracortical evoked potentials during classical aversive conditioning in cats.

In this article, intracortical evoked potentials (EPs) were recorded simultaneously from six different depths of the auditory cortex of freely moving cats. The effect of (a) different states of vigilance and that of atropine, (b) classical aversive conditioning, and (c) the effect of atropine during conditioning was studied on the intracortical EP profiles. Atropine induced EP changes that were similar to those seen in slow wave sleep. During classical aversive conditioning signal stimuli elicited a middle-latency negative EP component which was localized to the superficial cortical layers. Atropine (2 mg/kg body weight) did not abolish the appearance of this component but only increased its latency. It is proposed that the cholinergic part of the ascending activating system did not play an essential role in its generation.

Correlation between the Visceral Brain and the Brain Stem Maintenance in Equilibrium

In order to clarify the role of the amygdaloid nucleus in equilibrium function, the following experiments were carried out: nine electric stimuli, 0.1 msec, 200Hz pulse waves at 3 volts during a 30-second period were applied daily to a rabbit's amygdaloid nucleus (medial or lateral area).Optokinetic nystagmus and the EEG in response to optic stimulation were measured before and after the nine electric stimuli.In addition, the blood pressure was measured in rabbits with repeated electric stimulation of the medial or lateral area of the same amygdaloid nucleus. Stimulation was with 0.1 msec, 200Hz pulse waves at 30 volts for about 23 seconds.(1) Rabbits with repeated electric stimulation of the medial area of the amygdaloid nucleus tended to show increased optokinetic nystagmus and increased EEG activity in response to optic stimulation. Furthermore, their blood pressure increased when the medial area was stimulated.(2) Rabbits with repeated electric stimulation of the lateral area of the amygdaloid nucleus tended to show reduced optokinetic nystagmus and EEG activity and a decrease in blood pressure.The following conclusions were drawn:(1) The amygdaloid nucleus correlates with the brain stem, particularly the ascending activating system, in the maintenance of equilibrium.(2) The medial area of the amygdaloid nucleus actively participates in the maintenance of equilibrium function, promoting activity of the brain stem. The lateral area of the amygdaloid nucleus has an opposite function and seems to inhibit overexcitement of the brain stem, resulting in smooth maintenance of body equilibrium.

Role of the posterior hypothalamus in activity of the ascending activating system

In chronic experiments on cats after premesencephalic section of the brain stem electrical stimulation of the posterior hypothalamus evoked desynchronization of neocortical electrical activity. After isolated injury to the posterior hypothalamus, moderate electrical stimulation of the medial part of the mesencephalic reticular formation did not evoke any marked activation of the neocortex. The results point to the important role of the hypothalamus in the activity of the ascending activating system.

Arousal and the causation of behaviour.

Arousal and the causation of behaviour.

Influence of anticholinergic drugs on after-discharges and activity of epileptogenic foci in rabbit hippocampus

The influence of M-anticholinergic drug Metamyzil and N-anticholinergic drug Gangleron on the thresholds of after-discharges (AD) and the activity of a penicillin-produced epileptogenic focus in the hippocampus was studied in rabbits with chronic bipolar electrodes implanted in the cortex and subcortical structures. Both anticholinergics increased AD thresholds under direct administration into hippocampus at the point of stimulation (1–160 mkg). Metamyzil induced a more marked effect than Gangleron. When injected into the area of epileptogenic focus in the hippocampus, both anticholinergics (15–20 mkg) did not influence the intensity of interictal epileptiform discharges but decreased the number of fits. Gangleron equally affected the activity of the epileptogenic focus under both conditions of intravenous (1–3 mg/kg) and direct administration into the hippocampus. Contrary to Gangleron, when Metamyzil was intravenously administered (0.5–2.5 mg/kg) it markedly depressed the ascending activating system of the reticular formation and intensified interictal epileptiform activity and fits. It was concluded that the blocking of cholinergic systems of the hippocampus on one hand prevents the circulation of excitement along neuron circuits and, on the other hand, it does not influence the interictal epileptiform discharges in the EEG, which suggests that the fluctuation of the membrane potential of epileptogenic neurons were not affected.