B.K. Anand

Some aspects of electroencephalographic studies in Yogis

Abstract Four Yogis who practised samadhi were investigated electroencephalographically. It was observed that their resting records showed persistent alpha activity with increased amplitude modulation during samadhi. The alpha activity could not be blocked by various sensory stimuli during meditation. Two Yogis, who could keep their hand immersed in ice cold water for 45–55 min, also showed persistent alpha activity both before and during this practice. The possible mechanism of these observation has been discussed.

Electrical activity of the hypothalamic 'feeding centres' under the effect of changes in blood chemistry

Abstract Electrodes were stereotaxically implanted in the medial hypothalamic “satiety” and lateral “feeding” centres as well as in other hypothalamic and cerebral cortical regions. The electrical activity of these regions was recorded electroencephalographically. Changes in blood sugar, blood proteins and blood lipid contents were produced and their effects on the electrical activity observed. Hyperglycaemia increased the activity of the “satiety” centres and produced some drop in voltage in the electrical activity of the “feeding” centres. Hypoglycaemia decreased the activity of the “satiety” centres and occasionally slightly increased the activity of the “feeding” centres. No change in the activities of other areas was observed. Increased in blood proteins and blood lipid contents did not change the hypothalamic activity. It appears therefore, that the medial “satiety” regions of the hypothalamus show a glucoreceptor mechanism.

Effect of cyproheptadine on the electrical activity of the hypothalamic feeding centres

Abstract Electrodes were stereotaxically implanted in the lateral hypothalamic ‘feeding centre’ and medial ‘satiety centre’ as well as in other hypothalamic and cerebralcortical regions in cats. Electrical activity of these regions was recorded electroencephalographically, before and following i.v. injections of Periactin given daily for 7 days, in starving animals. In addition, changes in the eating behaviour, daily food intake, body weight as well as the arteriovenous glucose difference (to provide an index of glucose utilization in the body) were observed. Periactin injections produced hunger behaviour, increased food intake and gain in body weight. The EEG activity of the feeding centre showed an increase both in frequency and in amplitude, and this generally coincided with a decrease of glucose utilization in the body, with rise of both arterial and venous glucose level. The EEG activity of the satiety centre did not show any change, possibly as it was already low due to starvation. Similarly, other hypothalamic and cortical areas did not show any changes in their activity. Periactin injections also produced occasional paroxysms of drowsiness with the appearance of high voltage slow waves in all the EEG records.

Activity of single neurons in the hypothalamic feeding centers: Effect of 2-deoxy-d-glucose

Abstract Spontaneous activity of neurons of the ventromedial nucleus of hypothalamus (satiety center) and of the lateral hypothalamus (feeding center) was recorded in cats paralyzed with gallamine. Spontaneous discharges of satiety neurons were generally between 1 and 5 and of feeding neurons between 2 and 12 spikes per sec. When 2-deoxy-d-glucose, an analogue of glucose, was administered by slow intracarotid infusion, in a dosage of 100–200 mg/kg body weight, the frequency of units from the ventromedial nuclei was decreased to about 20 per cent of the normal, while that of units from lateral hypothalamus was increased to 16 per cent of the normal in a period of about 50 min. Saline infusion did not produce such an effect. Other units from anterior, middle and posterior hypothalamus also did not respond to infusions of 2-deoxy-d-glucose. With the dosage used in this study, 2-deoxy-d-glucose did not produce any generalized changes in blood sugar or an arterior-venous glucose difference in the cat. The significance of the specific response of hypothalamic feeding centers to glucopenia is discussed.

Effect of fenfluramine on the electrical activity of the hypothalamic feeding centers

Abstract Electrodes were stereotaxically implanted in the lateral hypothalamic feeding center and medial satiety center as well as in other hypothalamic and cerebral regions in male rhesus monkeys. Electrical activity of these regions was recorded electroencephalographically, before and following iv injections of Fenfluramine given daily for 7–10 days in doses of 1.5 mg/kg and 3 mg/kg body-weight respectively. In addition changes in the eating behavior, daily food intake, body weight and general behavior were observed. In another set of animals arteriovenous glucose differences (to provide indices of glucose utilization in the body) in response to Fenfluramine injections were estimated. Fenfluramine in doses of 1.5 mg/kg gradually resulted in slow wave activity in the feeding center, which became more pronounced after subsequent injections thus demonstrating a cumulative effect. This coincided with anorexic behavior and decrease in food intake. The activity of the satiety center changed to low voltage fast response, specially in starving animals. Arteriovenous glucose estimations suggest that the effects of Fenfluramine may be due to the increased level of glucose utilization in the body. Injections in doses of 3 mg/kg however produced a generalized drowsy response.

Electro-ontogenesis of cerebral and cardiac activities in the chick embryo

Abstract Spontaneous and metrazol-enhanced EEG activity was serially investigated in 55 chick embryos of 4 to 21 days incubation age. EKG was also recorded in 43 of these, either separately or simultaneously in 21. Occasional slow EEG waves, with intermittent silent intervals, were first recorded at the 4th day of incubation. These slow waves gradually became more regular and increased in amplitude as the days went by. By the 13th day fairly well marked low voltage fast activity appeared and became predominant in the later periods of incubation. On topical application of metrazol there was a potentiation of the cerebral activity, but no spikes appeared, and similar potentiation was occassionally produced by topical application of glucose, insulin and saline. Marked variations in rate, rhythm and regularity of the cardiac activity, with variable quiescent periods in between in younger ages, were recorded in different chick embryos. The EEG activity, however, did not show any variations between the rhythmically active or quiescent periods of the heart.

Influence of gonadal hormones and genital afferents on EEG activity of the hypothalamus in adult male rhesus monkeys

Electrodes were stereotaxically implanted in hypothalamic and cerebral cortical regions of 15 adult male gonadally intact rhesus monkeys. The electrical activity of these regions was recorded electroencephalographically before and after genital stimulation. Observations were also taken after stimulation on skin, abdomen and nipples and repeated daily for 4 to 6 days, before and after intravenous injections of testosterone propionate (0.4 mg/kg). The experiment was repeated on the same animal after gonadectomy. The influence of gential afferents appears to produce focal inhibition of electroencephalographic (EEG) activity in ventromedial nucleus (VMN) in monkeys with intact gonads. Exogenous administration of testosterone propionate produces EEG facilitation in VMN with simultaneous inhibition of the anterior hypothalamic area. With continued increase in amounts of circulating hormone, the EEG activity in the posterior hypothalamic area is also inhibited by the incoming genital afferent information. Gonadectomy brings about EEG slowing with genital stimulation in ventromedial nucleus before hormone injection but this was less marked than that observed in EEG records of intact preparation.

Effect of Fenfluramine on the single neuron activities of the hypothalamic feeding centers

Electrical activity of single neurons of the hypothalamic satiety and feeding centers and other adjacent areas was recorded by means of stereotaxically guided steel microelectrodes, before and after Fenfluramine infusion in doses of 1.5 mg/kg body wt. In addition arterial and venous blood glucose estimations were carried out to assess the levels of glucose utilization. The spike frequency of satiety center units increased while that of feeding center units decreased, in response to Fenfluramine while other hypothalamic units did not show any changes. The A-V glucose differences also increased showing increased level of glucose utilization. The significance of these findings in explaining the effects of Fenfluramine in depressing appetite have been discussed.

Electroencephalographic responses produced by genital stimulation and hormone administration in sexually immature rhesus monkeys

EEG activity from different hypothalamic, limbic and some other brain regions was recorded in unanaesthetised sexually immature male and female monkeys, through chronically implanted electrodes. On genital stimulation no specific changes in EEG responses were produced except a generalised arousal. Daily injections of testosterone given to male monkeys did not result in any specific EEG changes per se. Genital stimulation following this, however, resulted in high voltage low frequency waves mostly in the rostral hypothalamic regions. Daily injections of estrogen in female monkeys after a few days produced spontaneous spindling in the rostral hypothalamic regions, later on spreading to other areas. Genital stimulation following even the first estrogen injection produced spindling in the preoptic area. With spontaneous spindles appearing resultant to estrogen injections, genital stimulation further pronounced these.

Electrographic studies on the nature of sleep and wakefulness

Electroencephalographic activity of the neocortical gyri, ventral hippocampus, caudate nucleus and reticular formation (diencephalon to medulla) and other regions was investigated during natural sleep-wakefulness cycles spread over 88 sessions in 34 cats, free moving with implanted electrodes. The electrooculgram and the electromyogram of neck nuchal muscles were simultaneously recorded and correlated with the behavior. Regional EEG cycles differed in 4 ways: (a) those with synchronized EEG throughout the sleep and wakefulness, as in the ventral hippocampus, (b) those with desynchronised activity throughout, as in the bulbo-pontine reticular formation, (c) those with desynchronized EEG during wakefulness and active sleep and synchronized patterns during slow sleep, as in the neocortical gyri, caudate nucleus and near by regions, and (d) those that follow the pattern of (c) with slow waves superimposed, as in the mesencephalic reticular formation. Low voltage, low frequency stimulations given to the area lateral to the massa intermedia, nucleus reticularis pontis caudalis, nucleus reticularis ventralis, optic chiasma and the sciatic nerve induced EEG synchronization occasionally, but never an active sleep. A region more dynamogenic than the other diencephatic and reticular areas explored, was observed near the nucleus tractus trigemini. In view of the observations that the activation of restricted hypnogenic centres did not consistently produce somnolence and that the EEG changes during natural sleep-wakefulness cycles are simultaneous in the different regions and involve almost the whole structure of the brain, it is discussed that the involved integratory networks are likely to be much more extensive including the hypnogenic and the dynamogenic regions investigated here.