Lateral geniculate spikes in sleeping,awake, and reserpine-treated cats: Correlated excitability changes in superior colliculus and related structures

Spiking activity in lateral geniculate nucleus (LGN) may be recorded from cats during fast-wave sleep, with awake eye movements and following drug administration. The present experiments were undertaken to analyze visual system excitability changes correlated with these LGN spikes in fast-wave sleep, and to test whether comparable changes occur correlated with the LGN spikes in other conditions. Cats bearing chronically implanted electrodes were used to study the excitability of superior colliculus and related structures as a function of time during and following LGN spikes recorded under three conditions: fast-wave sleep; following reserpine administration; and with awake eye movements. Under these conditions, postsynaptic potentials in superior colliculus, cerebellum, pontine reticular formation, and visual cortex increased in amplitude throughout a 300-msec period beginning with the LGN spike. Eye movements elicited by optic nerve stimulation increased in amplitude along with postsynaptic potentials. Changes in response amplitude in all structures investigated were similar in the reserpinetreated and awake eye movement conditions to those of fast-wave sleep. This indicates that similar neuronal activity is associated with the LGN spikes of these three states. LGN spikes appear to signify neither a blanking circuit nor a corollary discharge, but rather are related to phasic activity in the midbrain reticular formation.     

Measuring spike strength in patients with continuous spikes and waves during sleep: Comparison of methods for prospective use as a clinical index

ObjectiveTo compare methods of estimating spike strength as a potential index in the assessment of continuous spikes and waves during sleep (CSWS).MethodsSpikes were searched and averaged automatically from pre- and postoperative EEGs of ten patients with CSWS who underwent corpus callosotomy (eight) or resective epilepsy surgery (two). From the most prominent spike, we measured peak amplitude and root mean square (RMS) over ±150 ms window around the peak. In order to compensate for spatiotemporal instability of spikes, the cumulative amplitude and RMS were computed from the highest quartile of electrodes (Ampl-Q and RMS-Q, respectively). The stability of parameters was studied by comparing two ten minute epochs during the first hour of NREM sleep, as well as by analyzing overnight variation of indices in further ten patients with CSWS. The Ampl-Q and RMS-Q were compared between pre- and postoperative recordings.ResultsAll four measures, amplitude, RMS, Ampl-Q and RMS-Q, were correlated with each other and highly dependent on NREM/REM-sleep stage and arousals. Expectedly, Ampl-Q and RMS-Q had the greatest intra-individual stability. The amplitude had up to 71% intra-individual variation making it unhelpful for clinical use. Ampl-Q and RMS-Q were comparable in assessing change following surgical treatment.ConclusionsComputing an integrated RMS over multiple electrodes during steady NREM sleep offers a stable and reliable parameter for evaluating the strength of spikes in CSWS.SignificanceAnalyzing spike strength with RMS-Q may offer a clinically useful, supplementary index for EEG monitoring of CSWS where spike index has been of limited value.     

Phasic activation of lateral geniculate and perigeniculate thalamic neurons during sleep with ponto-geniculo-occipital waves

Ponto-geniculo-occipital (PGO) waves are spiky field potentials generated in cholinergic nuclei of the dorsolateral mesopontine tegmentum just prior to and during rapid-eye-movement (REM) sleep and transferred toward thalamic nuclei. These events are commonly regarded as physiological correlates of oneiric behavior. We have examined the PGO-related discharges of physiologically identified neurons located in the dorsal lateral geniculate (LG) nucleus and perigeniculate (PG) sector of the reticular thalamic complex in chronically implanted, naturally sleeping cats. PGO focal waves and associated unit discharges were simultaneously recorded by the same microelectrode. PGO waves herald the other signs of REM sleep (EEG desynchronization and muscular atonia), appearing 30-90 sec before REM sleep over the EEG-synchronized activity of slow-wave sleep (pre-REM epoch). (1) Most PG neurons discharged bursts of action potentials in relation to PGO waves during both pre-REM and REM sleep. (2) The PGO-related activity of LG neurons was quite different. During the pre-REM stage, PGO waves correlated with a short (7-15 msec), high-frequency (300-500 Hz) spike burst of LG neurons, followed by a long (0.2-0.4 sec) train of single spikes, whereas during REM sleep, the PGO-related activity lacked the initial burst and consisted of a spike train that only slightly exceeded the tonically increased background firing of LG cells. The stereotyped characteristics of the PGO-related spike bursts during the pre-REM epoch suggest that they are the extracellular reflection of a low-threshold spike deinactivated by the tonic membrane hyperpolarization of LG cells associated with the EEG-synchronized sleep state. Such bursts are inactivated during the tonic depolarization of LG cells that occurs in REM sleep. The synchronous spike bursts discharged by LG cells in relation with the PGO waves of the pre-REM epoch probably underlie the much larger amplitude of the PGO waves of the pre-REM epoch as compared with those of the REM-sleep state. Since LG neurons have relatively low spontaneous firing rates during the EEG-synchronized pre-REM epoch, the PGO-related activity of this transitional stage leads to a higher signal-to-noise ratio in the visual thalamocortical channel than during REM sleep. We suggest that the PGO-related activity during the pre-REM epoch is related to vivid imagery during this stage of sleep.     

Effect of Isoflurane (Forane) on Intraoperative Electrocorticogram

Isoflurane, an inhalation agent often used for general anesthesia during craniotomy, has been reported to suppress spike activity in the intraoperative electrocor-ticogram (ECoG) during epilepsy surgery. We studied the effect of isoflurane concentrations of 0.25, 0.5, 0.75, 1, and 1.25% on the number of spike bursts per 5-min epochs in 15 patients undergoing ECoG during epilepsy surgery. N₂O in O₂ was maintained at 50% in 10 patients, at 60% in 2, and at 70% in 3. End tidal CO₂ concentration was maintained in the hypocarbic range, and analgesia was maintained with the narcotic alfentanil in the range of 0.5–2 μg/kg/min. The median number of spikes for each isoflurane concentration was 29 (range 3–107) at 0.25%, 27 (range 2–73) at 0.5%; 29 (range 5–90) at 0.75%, 33 (range 2–100) at 1%, and 40 (range 32–140) in 5 patients who tolerated 1.25% without occurrence of burst suppression pattern. No significant difference (Student's paired t test) was noted in the number of spikes for each isoflurane concentration. Therefore, if isoflurane concentrations are maintained between 0.25 and 1.25% or before burst suppression pattern occurs and N₂O/O₂ is maintained in the 50–70% range, isoflurane has no significant effect on spike activity.     

Functional brain connectivity in electrical status epilepticus in sleep

Aims. Electrical status epilepticus in sleep (ESES) is an age‐related, self‐limited epileptic encephalopathy. The syndrome is characterized by cognitive and behavioral abnormalities and a specific EEG pattern of continuous spikes and waves during slow‐wave sleep. While spikes and sharp waves are known to result in transient cognitive impairment during learning and memory tasks performed during the waking state, the effect of epileptiform discharges during sleep on cognition and behavior is unclear. There is increasing evidence that abnormalities of coherence, a measure of the consistency of the phase difference between two EEG signals when compared over time, is an important feature of brain oscillations and plays a role in cognition and behavior. The objective of this study was to determine whether coherence of EEG activity is altered during slow‐wave sleep in children with ESES when compared to typically developing children. Methods. We examined coherence during epochs of ESES versus epochs when ESES was not present. In addition, we compared coherence during slow‐wave sleep between typically developing children and children with ESES. Results. ESES was associated with remarkably high coherences at all bandwidths and most electrode pairs. While the high coherence was largely attributed to the spikes and spike‐and‐wave discharge, activity between spikes and spike‐and‐wave discharge also demonstrated high coherence. Conclusions. This study indicates that EEG coherence during ESES is relatively high. Whether these increases in coherence correlate with the cognitive and behavioral abnormalities seen in children with this EEG pattern remains to be determined.     

Spike patterns surrounding sleep and seizures localize the seizure-onset zone in focal epilepsy

Objective

Interictal spikes help localize seizure generators as part of surgical planning for drug-resistant epilepsy. However, there are often multiple spike populations whose frequencies change over time, influenced by brain state. Understanding state changes in spike rates will improve our ability to use spikes for surgical planning. Our goal was to determine the effect of sleep and seizures on interictal spikes, and to use sleep and seizure-related changes in spikes to localize the seizure-onset zone (SOZ).

Methods

We performed a retrospective analysis of intracranial electroencephalography (EEG) data from patients with focal epilepsy. We automatically detected interictal spikes and we classified different time periods as awake or asleep based on the ratio of alpha to delta power, with a secondary analysis using the recently published SleepSEEG algorithm. We analyzed spike rates surrounding sleep and seizures. We developed a model to localize the SOZ using state-dependent spike rates.

Results

We analyzed data from 101 patients (54 women, age range 16–69). The normalized alpha-delta power ratio accurately classified wake from sleep periods (area under the curve = .90). Spikes were more frequent in sleep than wakefulness and in the post-ictal compared to the pre-ictal state. Patients with temporal lobe epilepsy had a greater wake-to-sleep and pre- to post-ictal spike rate increase compared to patients with extra-temporal epilepsy. A machine-learning classifier incorporating state-dependent spike rates accurately identified the SOZ (area under the curve = .83). Spike rates tended to be higher and better localize the seizure-onset zone in non–rapid eye movement (NREM) sleep than in wake or REM sleep.

Significance

The change in spike rates surrounding sleep and seizures differs between temporal and extra-temporal lobe epilepsy. Spikes are more frequent and better localize the SOZ in sleep, particularly in NREM sleep. Quantitative analysis of spikes may provide useful ancillary data to localize the SOZ and improve surgical planning.     

The role of the temporal lobe amygdala in ponto-geniculo-occipital activity and sleep organization in cats

Ponto-geniculo-occipital (PGO) spikes propagate to different structures of the limbic system, including the temporal lobe amygdala. There is direct connection between the amygdala and the pontine nuclei involved in the generation of PGO spikes. It has also been shown that both the amount and the pattern of PGO spike discharges are under the influence of several brainstem and forebrain structures. In the present work, PGO activity was analyzed in unrestrained cats submitted to low-intensity amygdaloid electrical stimulation during paradoxical sleep (PS) episodes. General sleep organization as well as number, mean duration and percentage of PS episodes, were assessed in 8-h sleep recordings during amygdaloid stimulation. Amygdaloid stimulation significantly increased PGO number, spike density and, specially, PGO burst density. No significant changes were found in PS episodes or in the slow-wave sleep. It is concluded that the amygdala plays a role in the modulation of PGO activity by means of a facilitatory influence. It is proposed that this influence is probably exerted through a positive feedback mechanism. The independence between PGO generation and PS maintenance mechanisms is emphasized.     

Sleep modulation of interictal spike configuration in untreated children with partial seizures

Spontaneous changes in interictal spike morphology were evaluated before initiation of antiepileptic drug (AED) therapy in 38 children with uncontrolled partial seizures. Nonrapid eye movement (NREM) sleep during the first third of the night was associated with spikes of higher amplitude, longer duration, and lower degree of sharpness than those observed in wakefulness or REM sleep. Spike amplitude decreased in subsequent NREM epochs, but duration and sharpness remained relatively consistent. A NREM/REM modulatory pattern was identified, with REM periods exhibiting spikes of decreased amplitude, shorter duration, and increased sharpness as compared with NREM periods in each third of the night. The spike changes associated with REM sleep are similar to the alterations previously described as occurring coincidentally with attainment of seizure control and thus may reflect inherent modulation of epileptogenicity in synchrony with sleep cycles.     

Benign EEG variants in the sleep–wake cycle: A prospective observational study using the 10–20 system and additional electrodes

ObjectivesTo study the prevalence of benign EEG variants (BEVs) in the sleep–wake cycle among 1163 consecutive patients.MethodsProspective, observational EEG study using the 10–20 system with systematically two additional anterior-temporal electrodes. Depending on clinical indications, other electrodes were added. REM sleep identification was based on its characteristic EEG grapho-elements and rapid eye movements, clearly detectable with the additional anterior-temporal and fronto-polar electrodes due to eye proximity. The video-EEG monitoring duration was between 24 hours and eight days.ResultsWe identified 710 patients (61%) with BEVs. Positive occipital sharp transients of sleep (POSTs) were observed in 36.4% of participants, mu rhythm in 22.4%, lambda waves in 16.7%, wicket spikes (WS) in 15%, 14- and 6-Hz positive bursts in 8.3%, benign sporadic sleep spikes (BSSS) in 3.3%, rhythmic mid-temporal theta burst of drowsiness (RMTD) in 2.15%, midline theta rhythm in 2.1% and six-Hz spike and wave (SW) bursts in 0.1%. WS and RMTD were present during wakefulness, NREM (14.1%, 1.3%, respectively) and REM sleep (3.3%, 1.1%, respectively). Mu rhythm was also observed during NREM (1.5%) and REM sleep (7.7%). Fourteen- and 6-Hz positive bursts were present during NREM (4.5%) and REM sleep (6.5%). BSSS and six-Hz SW bursts were only observed during NREM sleep.ConclusionsThe prevalence of BEVs is much higher than current estimates. POSTs and WS can no longer be considered as unusual patterns but physiological patterns of NREM sleep. RMTD and mu rhythm may be observed during NREM and REM sleep.     

Influences of hippocampal place cell firing in the awake state on the activity of these cells during subsequent sleep episodes

Rat hippocampal (CA1) complex spike "place cells" of freely behaving rats were recorded in pairs continuously during a series of waking (exploration and still-alert), drowsy (quiet-awake), and sleeping (slow-wave, pre-rapid-eye-movement and rapid-eye-movement sleep) behaviors. Pairs of units were selected that had nonoverlapping place fields. The rats were restricted from entering the place field of either cell overnight, and on the day of recording cells were exposed to their individual place fields independently and in a counterbalanced manner. Following exposure, recordings were made in the subsequent sleep episodes and the firing characteristics of both cells were analyzed. Following exposure, significant increases in the spiking activity of the exposed cell were observed in the subsequent sleeping states that were not evident in the unexposed cell. The increased activity was observed in the rate of firing (spikes/sec), the rate of occurrence of bursts with multiple spikes, as well as the number of bursts displaying short (2-4 msec) interspike intervals. The findings suggest that neuronal activity of hippocampal place cells in the awake states may influence the firing characteristics of these cells in subsequent sleep episodes. The increased firing rates along with the greater number of multiple spike bursts and the shorter interspike intervals within the burst, following exposure to a cell's place field, may represent possible information processing during sleep.     

Lateral geniculate spikes, muscle atonia and startle response elicited by auditory stimuli as a function of stimulus parameters and arousal state

We have investigated the motor and ponto-geniculo-occipital (PGO) wave response to startle eliciting stimuli in the unanesthetized cat. We found that the amplitude of the PGO spike recorded in the lateral geniculate nucleus (LGN) increases monotonically with increasing intensities of auditory stimuli. In contrast, the motor response to low intensity (less than 75 dB) stimuli is characterized by electromyographic (EMG) suppression, while at higher intensities an EMG excitation is superimposed on this suppression. Thus PGO elicitation is accompanied by EMG suppression at low intensities and by a net EMG excitation at high intensities. While the amplitude of the auditory elicited PGO response is a graded function of stimulus intensity, somatic stimuli tend to elicit the PGO response in all-or-none fashion. Both the motor and PGO responses to sensory stimulation change with behavioral state. The EMG suppression by auditory stimulation increases in duration during the transition to rapid eye movement (REM) sleep. Elicited PGO amplitude is highest in transitional sleep, lower in quiet waking and REM sleep and lowest in active waking. Prepulse inhibition of PGO spikes is greatly attenuated during transitional and REM sleep. We hypothesize the existence of 3 phasic response systems, a motor suppression system, a motor excitation (startle) system and a PGO elicitation system. While these systems are triggered concurrently by intense phasic stimuli in waking, they are modulated independently by stimulus intensity and behavioral state, and have different rates of habituation. These systems act in concert to produce behavioral responses to sudden onset stimuli.     

Magnetoencephalography localizing spike sources of atypical benign partial epilepsy

Rationale: Atypical benign partial epilepsy (ABPE) is characterized by centro-temporal electroencephalography (EEG) spikes, continuous spike and waves during sleep (CSWS), and multiple seizure types including epileptic negative myoclonus (ENM), but not tonic seizures. This study evaluated the localization of magnetoencephalography (MEG) spike sources (MEGSSs) to investigate the clinical features and mechanism underlying ABPE. Methods: We retrospectively analyzed seizure profiles, scalp video EEG (VEEG) and MEG in ABPE patients. Results: Eighteen ABPE patients were identified (nine girls and nine boys). Seizure onset ranged from 1.3 to 8.8 years (median, 2.9 years). Initial seizures consisted of focal motor seizures (15 patients) and absences/atypical absences (3). Seventeen patients had multiple seizure types including drop attacks (16), focal motor seizures (16), ENM (14), absences/atypical absences (11) and focal myoclonic seizures (10). VEEG showed centro-temporal spikes and CSWS in all patients. Magnetic resonance imaging (MRI) was reported as normal in all patients. MEGSSs were localized over the following regions: both Rolandic and sylvian (8), peri-sylvian (5), peri-Rolandic (4), parieto-occipital (1), bilateral (10) and unilateral (8). All patients were on more than two antiepileptic medications. ENM and absences/atypical absences were controlled in 14 patients treated with adjunctive ethosuximide. Conclusion: MEG localized the source of centro-temporal spikes and CSWS in the Rolandic-sylvian regions. Centro-temporal spikes, Rolandic-sylvian spike sources and focal motor seizures are evidence that ABPE presents with Rolandic-sylvian onset seizures. ABPE is therefore a unique, age-related and localization-related epilepsy with a Rolandic-sylvian epileptic focus plus possible thalamo-cortical epileptic networks in the developing brain of children.     

Somatic reflex response-reversal of reticular origin

This study was undertaken in order to determine the role played by the ponto-mesencephalic reticular formation in regulating somatic reflex activity during states of sleep and wakefulness. The amplitude of the brain stem masseteric (jaw closing) reflex, induced continuously in freely-moving adult cats, served as a baseline control for this analysis of reflex modulation. At randomly-spaced intervals, high frequency stimulation was applied to the ponto-mesencephalic reticular formation for 4-sec periods. In the states of wakefulness and quiet sleep, the amplitude of the masseteric reflex increased significantly during superimposed reticular stimulation. When the animal entered into active sleep, however, the result of reticular stimulation (using identical parameters) was a profound decrease in reflex amplitude. This single neural region, then, previously thought to be responsible only for facilitation of somatic motor activity, appears to be capable of expressing another diametrically opposite function, i.e., reflex inhibition. Thus, a role is suggested for the ponto-mesencephalic reticular formation in the modulation of somatic motor activity, not only during wakefulness, but also throughout sleep. Since the direction of reflex control is governed by the state of the animal, this region of the brain may also be responsible for the state of the animal itself.     

NMDA receptor antagonists attenuate a portion of the penicillin-induced epileptiform burst

In the CA1 region of the rat hippocampal slice, epileptiform activity was induced by the GABAA antagonist penicillin (PEN, 3.4 mM). The competitive N-methyl-D-aspartate (NMDA) receptor antagonists D-2-amino-7-phosphonoheptanoate (D-AP7) and D-2-amino-5-phosphonovolerate (D-AP5) attenuated extracellularly recorded evoked burst duration, the number of population spikes per evoked bursts and the frequency of spontaneously occurring bursts, but did not affect the sum of the population spike amplitudes or the evoked burst coastline measures due to increases in amplitude of the remaining secondary population spikes. Intracellular recordings showed that many of the secondary action potentials in the PEN burst were decreased in amplitude and broadened in duration, perhaps due to spike inactivation. D-AP7 allowed these secondary action potentials to increase in amplitude, which could explain the increases in secondary population spike amplitude seen extracellularly. Decrements in stimulus strength can mimic the effect of D-AP7 on PEN bursts. These data suggest that there is a portion of the PEN-induced epileptiform burst which is sensitive to NMDA antagonists.     

Evidence for two types of firing pattern during the sleep-waking cycle in the reticular thalamic nucleus of the cat

The activity of 23 neurons was recorded extracellularly in the nucleus reticularis thalami (RT) of four chronically implanted cats. Patterns of discharge were studied and their relationship to wakefulness (W), slow-wave sleep (SS), and paradoxical sleep (PS) were examined. The firing pattern was analyzed using zero-order (firing rate), first-order (interspike interval histogram), and second-order (joint interval histogram and autocorrelogram histogram) statistics. The SS bursting pattern was investigated taking into account the duration of the intervals between the bursts, the number of spikes per burst, and the duration of the bursts. Zero- and first-order characterizations during W and PS were found to be comparable. However, the joint interval histogram revealed a state-specific pattern during W for 74% of the cells. This pattern was characterized by a nonrandom occurrence of some categories of adjacent intervals. This was not found during PS. Two-thirds of the cells recorded, called “fast” neurons, exhibited firing rates higher than 15 spikes/s during W and PS. Those remaining, called “slow” neurons, showed a mean discharge rate lower than 10 spikes/s. In SS “fast” neurons fired long-duration bursts with interburst intervals generally shorter than 1 s. Conversely, “slow” neurons discharged shortduration bursts interrupted by long interburst intervals (greater than 1 s). Nevertheless, both types of cells had the same number of spikes within the burst and a similar intraburst pattern. Approximately half of the cells studied depicted a “slow rhythm” in the autocorrelogram histogram. Its periodicity was independent of firing rates and behavioral states.     

Different cellular types in mesopontine cholinergic nuclei related to ponto-geniculo-occipital waves

The only mesopontine neurons previously described as involved in the transfer of ponto-geniculo-occipital (PGO) waves from the brain stem to the thalamus were termed PGO-on bursting cells. We have studied, in chronically implanted cats, neuronal activities in brain-stem peribrachial (PB) and laterodorsal tegmental (LDT) cholinergic nuclei in relation to PGO waves recorded from the lateral geniculate (LG) thalamic nucleus during rapid-eye-movement (REM) sleep. We constructed peri-PGO histograms of PB/LDT cells' discharges and analyzed the interspike interval distribution during the period of increased neuronal activity related to PGO waves. Six categories of PGO-related PB/LDT neurons with identified thalamic projections were found: 4 classes of PGO-on cells: PGO-off but REM-on cells: and post-PGO cells. The physiological characteristics of a given cell class were stable even during prolonged recordings. One of these cell classes (1) represents the previously described PGO-on bursting neurons, while the other five (2-6) are newly discovered neuronal types. (1) Some neurons (16% of PGO-related cells) discharged stereotyped low-frequency (120-180 Hz) spike bursts preceding the negative peak of the LG-PGO waves by 20-40 msec. These neurons had low firing rates (0.5-3.5 Hz) during all states. (2) A distinct cell class (22% of PGO-related neurons) fired high-frequency spike bursts (greater than 500 Hz) about 20-40 msec prior to the thalamic PGO wave. These bursts were preceded by a period (150-200 msec) of discharge acceleration on a background of tonically increased activity during REM sleep. (3) PGO-on tonic neurons (20% of PGO-related neurons) discharged trains of repetitive single spikes preceding the thalamic PGO waves by 100-150 msec, but never fired high-frequency spike bursts. (4) Other PGO-on neurons (10% of PGO-related neurons) discharged single spikes preceding thalamic PGO waves by 15-30 msec. On the basis of parallel intracellular recordings in acutely prepared, reserpine-treated animals, we concluded that the PGO-on single spikes arise from conventional excitatory postsynaptic potentials and do not reflect tiny postinhibitory rebounds. (5) A peculiar cellular class, termed PGO-off elements (8% of PGO-related neurons), consisted of neurons with tonic, high discharge rates (greater than 30 Hz) during REM sleep. These neurons stopped firing 100-200 msec before and during the thalamic PGO waves. (6) Finally, other neurons discharged spike bursts or tonic spike trains 100-300 msec after the initially negative peak of the thalamic PGO field potential (post-PGO elements, 23% of PGO-related neurons).(ABSTRACT TRUNCATED AT 400 WORDS)     

Recovery curves of the blink reflex during wakefulness and sleep

Summary The paired shock technique was used to study the effect of sleep on the excitability of the short latency R₁ and long latency R₂ components of the electrically elicited blink reflex. During wakefulness, R₁ returned, after transient potentiation, to its original level in about 150 ms following the conditioning stimulus. Contrastingly, R₂ remained profoundly suppressed up to 800 ms, suggesting sustained reduction of excitability of the polysynaptic reflex pathways after the passage of a preceeding impulse. During non-REM and REM sleep, the recovery curve of R₁ was similar in character, although different in time course to the one obtained during wakefulness. However, R₂ was potentiated rather than suppressed by the conditioning stimulus during both phases of sleep. These findings indicate that, during sleep, the polysynaptic reflex pathways are not inhibited by a preceeding impulse to the same degree as in wakefulness.A part of this study was done when the authors were associated with the Department of Internal Medicine (Neurology), Faculty of Medicine, University of Manitoba.     

An Electroencephalographic Study of Nocturnal Sleep in Temporal Lobe Epilepsy

• 1) A whole night EEG study was carried out on twenty temporal lobe epileptics and fourteen normal subjects. ECG, respiratory curve, GSR and horizontal eye movements were also simultaneously recorded polygraphically. Primary attention was devoted to the changes of temporal spikes in different stages of nocturnal sleep and also to the characteristics of sleep course of the patients.
• 2) The electrographic depth of sleep was divided into the following five stages; A (wakefulness), B (drowsiness and light sleep), C (moderately deep sleep), D (deep sleep) and P (paradoxical phase of sleep or REM sleep). The sleep diagrams were drawn on all the patients and the rate of incidence of spike discharges throughout a whole night was demonstrated in each stage of sleep on seven patients.
• 3) As to the pattern of sleep cycles during a whole night, the majority of twenty patients with temporal lobe epilepsy showed some disorganizations of the pattern of sleep cycles to more or less degree. Although there were great individual differences, the most characteristic features observed on the sleep course of the patients were prolongation and frequent appearance of C stage, shortening or poor appearance of D stage and irregular appearance of P stage. These changes were observed more remarkably in younger patients. The disorganizations of sleep cycles observed on temporal lobe epileptics seemed partly due to the dysfunctions or lesions of limbic system of the brain. Spindle-formed rhythmical waves with frequencies ranging from 8 to 12 c/s were found during C stage of the patients. The lower voltage of delta waves during the deepest stage of sleep and the poor appearance of humps during light stage of sleep were also observed.
• 4) The most frequent incidence of temporal spikes was observed during C stage on most of the patients. Only a few patients showed the most frequent incidence of spikes during B stage. No clear correlation was found between the types of the incidence of spike discharges and etiological or clinical factors. During P stage, spike discharges were generally suppressed as well as during A stage in most of the patients. On the patients with bilateral multifoci, the mode of incidence of spikes during sleep almost the same in both hemispheres.
• 5) Nine clinical seizures were observed on seven patients during nocturnal recordings. Two seizures occurred during C stage, three during D stage, three during P stage and one during B stage. On a female patient, three seizures were provoked during B stage and P stage in one night. So the predilected depth of sleep for nocturnal seizures was never found in this study. After clinical seizures, the depth of sleep did not alter, the patients did not generally awake and could not remember their nocturnal fits next morning. Ictal EEG patterns were rhythmic slow waves started at the region of the EEG spike focus with a exception of a case which showed irregular spike and wave complex.
• 6) The neuronal mechanisms underlying the modifications of incidence of spike discharges during sleep were discussed in terms of interrelation between the activity level of the brain and the mechanism producing seizure discharges.

     

The role of pedunculopontine nucleus in isolated REM sleep behavior disorder and REM sleep without atonia

IntroductionThe aim of this study was to analyze the functions of pedunculopontine nucleus (PPN) in isolated REM sleep behavior disorder (iRBD) and REM sleep without atonia (RSWA) to investigate the role of PPN in dream-enacting motor behaviors in RBD. We evaluated the activity of PPN through the prepulse modulation (PPM) together with other brainstem reflexes to investigate the differences in changes at brainstem.MethodsWe included nine patients with isolated RSWA and 10 patients with iRBD. For diagnosis, all patients underwent polysomnography. None of the patients had parkinsonism or dementia. We also included 17 healthy participants with similar age and sex. Blink reflex (BR), PPM of BR, recovery excitability of BR, and auditory startle reflex (ASR) were recorded in all participants.ResultsThere was a prepulse inhibition deficit in iRBD and RSWA groups compared to healthy subjects. The BR-R2 recovery at 200 ms interval was also higher in patients with iRBD and RSWA. In ASR recordings, the response probabilities were higher in the RBD group compared to RSWA and control groups.ConclusionThe PPM was abnormal in both iRBD and RSWA whereas ASR was enhanced in iRBD. We suggest that there are certain similarities and differences in the pathophysiologies of iRBD and RSWA.     

Effects of optic nerve section in baboons on the geniculate and cortical spike activity during various states of vigilance]

Eye movement potentials during wakefulness (EMPs) and so-called spike (PGO) activities were studied in 4 adult baboons before and after optic nerve (ON) section. The latter was performed either in two stages at a 23-day interval or simultaneously. During wakefulness in the intact animal, triphasic EMPs were observed in darkness with smaller amplitude and longer duration than in the light. After section of one ON, the 3 EMP components persisted, but with a smaller amplitude of the first wave. After section of the second ON morphological changes appeared: the amplitude and duration of the potentials were intermediate between those noted in darkness and light but with an intermingled sharp spike. Geniculate EMPs reappeared 11 days after simultaneous ON section, with the same evolution as previously described. During slow wave and REM sleep, intact animals presented lateral geniculate (LG) monophasic and biphasic spikes, called spikes I and II. At the cortex, they occurred either generalized or limited to one area (anterior or posterior) and were called pontogeniculocortical spikes (PGC). After section of one ON, the pattern of occurrence of phasic activities remained identical in LG. Sharp spikes (spike III) appeared; then their occurrence increased. At the end of the second month after the second section, only spikes II and III remained, spike I disappearing, while PGC amplitude diminished. When both ONs were cut simultaneously, spike III was observed from the first day and PGC activity tended to disappear partially for 11 days. Their later evolution was similar to that noted previously. However, changes were seen earlier (the highest rate of spike III occurring at day 35). In both cases, PGC spikes at the cortex increased in amplitude and frequency of occurrence.