Phasic motor activity reduction occurring with horizontal rapid eye movements during active sleep in human

Theta wave amplitude and frequency are differentially correlated with pontine waves and rapid eye movements during REM sleep in rats

The present study examined the correlations between the dynamics of hippocampal theta waves and pontine waves (P waves) and rapid eye movements (REMs) densities during REM sleep. Theta wave peak frequency and theta amplitude were estimated as the parameters of theta wave dynamics in each 3s segment. The peak frequency and theta amplitude were positively correlated with P wave and REMs densities, however their detailed correlation properties were distinct from each other. Dependency of peak frequency on P wave/REMs density did not change significantly from that on REMs/P wave density. On the other hand, dependency of the theta amplitude on P wave/REMs density significantly increased with an increased REMs/P wave density. Because hippocampal theta waves and P waves are involved in learning and memory functions during REM sleep, the correlation between theta parameters and P wave density might help to clarify these functions.

Disturbance of phasic chin muscle activity during rapid-eye-movement sleep

In patients with Rett syndrome (RS), a peculiar type of disturbance in phasic chin muscle activity during rapid-eye-movement sleep (REMS) (e.g. an elevation of phasic inhibition index (PII) without an affection of tonic inhibition index (TII)) has been reported. The similar disturbance in REMS was reported not only in child patients with infantile spasms, severe myoclonic epilepsy in infancy (SMEI), severe nocturnal enuresis, and autism but also in adult patients with Parkinson's disease (PD). Except for SMEI and PD, patients with the other four clinical entities including RS could express autistic tendency. Since the responsible lesion for the occurrence of an elevation of PII with a normal TII value is likely to be in the pontine tegmentum, this subcortical structure is hypothesized to be involved in the appearance of autistic tendency.

Neurophysiology of Rett syndrome

Neurophysiological studies on Rett syndrome (RTT) are reviewed, and pathophysiology of RTT is discussed. The electroencephalography (EEG), sensory evoked potentials (SEP), sleep-wake rhythm study and polysomnography (PSG) study showed age-dependent characteristics. PSG revealed the brainstem and midbrain monoaminergic systems are deranged from early developmental stage, that is serotonin and noradrenaline systems seem to be hypoactive and dopaminergic system is also hypoactive associated with receptor supersensitivity. These monoaminergic systems are known to influence the maturation of the higher neuronal systems at specific areas and at specific ages. Particularly the synaptogenesis of the cerebral cortex is modulated by region or layer specifically from an early stage of the development. The observations made in EEG and SEP studies also suggested specific subcortical and cortical involvements taking place during the development. The age-dependent appearance of characteristic clinical features of RTT, and the variation of the clinical severities, e.g. classical, variant, form fruste, etc., can also be explained by the specific features of these monoaminergic systems. Furthermore, analysis of the components of rapid eye movement sleep suggested the onset of RTT lies between 36 gestational weeks to 3-4 months postnatally. The discovery of the mutations of methyl-CpG-binding protein 2 (MECP2) gene as the causative gene of RTT is an epoch helping not only to understand the pathophysiology of RTT but also various neurodevelopmental disorders.

Polysomnographical assessment of the pathophysiology of West syndrome

In this brief review, the sleep studies on patients with West syndrome (WS) were summarized. In addition to the previously reported common finding for sleep in WS--reduction of the amount of rapid-eye-movement (REM) sleep--weakness of phasic suppression of chin muscle activity in WS patients has recently been found. The degree of this weakness is quantified by the phasic inhibition index (PII), which has been found to reflect a patient's prognosis as to convulsions. PII is proposed to be a useful parameter for assessing the prognosis of WS. Since the pontine tegmentum is involved in the production of the REM-related phasic loss of muscle activity in REM sleep, WS patients are hypothesized to have a functional instability of the pontine tegmentum. After adrenocorticotropin (ACTH) treatment, PII decreased significantly in all WS patients examined. Taken together with the effects of corticosteroids on PII, and the incidence of phasic chin muscle activity in patients with congenital adrenal hyperplasia and nephrotic syndrome, ACTH is hypothesized to suppress the spasms in WS patients not only through corticosteroids, but also through a direct action on the pontine tegmentum. Since PII has been reported to be elevated in patients with an autistic tendency, the appearance of an autistic tendency is also hypothesized to be involved in the functional disturbance of the pontine tegmentum.

Bilateral phrenic nerve palsy as a complication of anterior decompression and fusion for cervical ossification of the posterior longitudinal ligament

STUDY DESIGN

A case report of bilateral phrenic nerve palsy as a complication of anterior decompression and fusion for cervical ossification of the posterior longitudinal ligament (OPLL).

OBJECTIVES

To present a case of a rare and serious complication of cervical spinal surgery and to investigate its cause.

SUMMARY OF BACKGROUND DATA

There have been a number of reports of phrenic nerve palsy after cardiac surgery, but the authors have found no previous description of this complication related to spinal surgery.

METHODS

The authors describe the clinical presentation and management of a case of bilateral phrenic nerve palsy subsequent to the surgery for cervical OPLL. Also, the literature is reviewed concerning surgical approaches for the treatment of OPLL and the occurrence of phrenic nerve palsy subsequent to any form of therapy.

RESULTS

Bilateral phrenic nerve palsy occurred after anterior decompression and fusion for cervical OPLL. Bilateral phrenic nerve palsy was diagnosed radiographically: postoperative chest radiograph showed bilateral laxity of the diaphragm. Movement of the bilateral diaphragm appeared 3 weeks after surgery. The patient successfully returned to normal daily life after ventilatory support for 3 months, although nocturnal oxygen support was still necessary at the latest follow-up, 3 years after surgery. The possible causes of this complication include bilateral C4 nerve root stretching, iatrogenic injury of the gray matter in the ventral horn, alteration of blood circulation related to spinal edema, or re-impingement on the spinal cord at the cranial part of the decompression site.

CONCLUSIONS

Bilateral phrenic nerve palsy occurred after anterior decompression and fusion for cervical OPLL. Bilateral phrenic nerve palsy should be kept in mind as a serious complication of spinal surgery. It should be considered when patients unexpectedly fail to wean from the ventilator after surgery.

Asynchronous breathing during sleep

BACKGROUND

Children rarely complain of symptoms associated with sleep disordered breathing (SDB). Paradoxical inward rib cage movement (PIRCM) during sleep might prove useful for detecting SDB.

AIMS

(1) To determine the correlation between the degree of PIRCM and other measures of disordered breathing during sleep. PIRCM occurs physiologically throughout rapid eye movement sleep in neonates, while no PIRCM has been reported during sleep in adolescents. (2) To determine the chronological changes in the degree of PIRCM.

METHODS

PIRCM was quantified by means of the laboured breathing index (LBI). LBI was determined by respiratory inductive plethysmography; PIRCM accompanies a high LBI. Sleep recordings obtained for 101 subjects for various reasons (aged from 3.5 months to 19 years) were analysed.

RESULTS

In 22 records, the minimum SaO2 value was 90% or more and no obstructive apnoea of more than 10 seconds was observed. In these 22 records, LBI during rapid eye movement sleep decreased significantly with age, reaching the mature low level at 3.3 years of age. In the other 79 records, LBI correlated well with measures of obstructed breathing during sleep.

CONCLUSIONS

By paying more attention to PIRCM, more obstructed breathing during sleep might be found among children aged 3 years or more.

REM sleep atonia: responsible brain regions, quantification, and clinical implication

Muscle tone is profoundly suppressed during rapid-eye-movement sleep. Two indices that quantify this muscle activity suppression were introduced: the tonic inhibition index (TII) and the phasic inhibition index (PII). TII expresses the shortening of phasic chin muscle activity, and PII indicates the degrees of suppression of the occurrence of phasic chin muscle activity in the period of the burst of rapid eye movements. TII increased significantly with age, while PII decreased significantly. TII was found to reach the adult level at 12.3 years of age, while PII decreased to the adult value at 0.4 years. According to this difference in age between their maturation, the human nervous systems involved in muscle activity suppression are hypothesized to comprise at least two independent systems. TII and PII are also hypothesized to be affected by the activity of the brainstem inhibitory centers, which might be implicated in the suppression of muscle activity during wakefulness as well.

REM sleep components predict the response to initial treatment of infantile spasms

PURPOSE

The phasic inhibition index (PII) is the rate of the simultaneous occurrence of rapid eye movement bursts (RBs) and phasic chin muscle activity (PCMA) during rapid eye movement sleep (REMS). PII is low insofar as physiologically occurring REM-related phasic inhibition acts on chin muscles. Previously we found that PII was significantly higher in patients with infantile spasms (ISs) who had a recurrence of convulsions than in patients with ISs who exhibited no recurrence. We aimed to predict the response of patients with ISs to conventional anticonvulsants (AEDs) by means of REMS components including PII, expecting to facilitate avoidance of potentially hazardous hormonal therapy.

METHODS

REMS, recorded before the beginning of any medication, was retrospectively examined in 15 patients with ISs. The patients were classified into two groups according to the response to initial treatment with conventional AEDs. Conventional AEDs were enough to control the spasms in six good responders (GRs), whereas further hormonal therapy was required in nine poor responders (PRs) to control the spasms.

RESULTS

The amount of REMS was significantly lower in patients with ISs than in controls. GRs had less REMS than did PRs, although no significant difference was observed. Although the frequencies of RB and PCMA showed no significant differences among GRs, PRs, and controls, the average PII value in PRs (12.6+/-3.4; mean+/-SD) was significantly (p < 0.001) higher than that in GRs (6.1+/-1.7).

CONCLUSIONS

PII is a useful parameter for differentiating GRs from PRs.

Development of REM sleep atonia

OBJECTIVES

To study the functional development of neuronal systems that suppress muscle activity, we quantified the chronological change of atonia in rapid-eye-movement sleep (REMS).

METHODS

REMS atonia was quantified by the tonic and phasic inhibition indices (TII and PII). TII indicates the shortness of chin muscle activity, whereas PII standardizes the simultaneous occurrence of chin muscle activity and bursts of rapid eye movements. TII and PII were calculated in REMS of 135 polysomnographical recordings obtained in healthy humans from premature babies to a 77-year-old man.

RESULTS

TII increased significantly with age, while PII decreased significantly. TII reached an adult level at preadolescence, while PII at early infancy.

CONCLUSION

Human nervous systems involved in both tonic and phasic inhibition in REMS raise their activities with age. Since TII and PII reach adult levels at different ages, suppression of muscle activity is hypothesized to be mediated through at least 2 independent systems in humans.

Changes in reflex responses of the masseter and digastric muscles during sleep in freely behaving rabbits

The aim of this study was to clarify the modulation of motoneuron excitability in masticatory muscles during sleep. For this purpose, changes in the reflex responses of the masseter and digastric muscles between sleep and wakefulness were studied in freely behaving rabbits. Stimulation of the jaw closing muscle spindle afferents induced the masseteric monosynaptic reflex (MMR). During quiet sleep (QS), which gradually replaced quiet wakefulness, the mean MMR amplitude showed no change. During active sleep (AS). MMR amplitudes were markedly reduced, but they were confounded by the occasional occurrence of facilitation in the amplitude. The facilitatory reflexes were often related to rapid eye movements (REMs). However, the excitatory input probably did not originate from the same region as the REM generator, since the REM and the large MMR did not always occur simultaneously. On the other hand, jaw opening reflexes remained inhibited. The results indicated that there is mainly a difference in the excitability between the two groups of motoneurons during AS; masseter motoneuron activity was inhibited but occasionally facilitated by excitatory inputs occurring in association with REMs, however, the digastric motoneuron activity was remained inhibited. The excitatory inputs may induce dysfunctional muscle contraction of the jaw closing muscles as seen in bruxism.

Reticulospinal systems mediate atonia with short and long latencies

The pontomedullary region is responsible for both the tonic and phasic reduction of muscle activity in rapid-eye-movement sleep and contributes to the control of muscle tone in waking. This study focused on determining the time course of activity in the pontomedullary systems mediating atonia. Short-train stimulations (3 0.2-ms pulses at 330 Hz) of the pons and medulla suppressed neck and hindlimb muscle activity in decerebrate cats. We identified two distinct phases of suppression, early and late. The anatomic sites that produced each suppression were intermixed. We estimated the dividing value of the conduction velocity for reticulospinal projections responsible for early and late phases of hindlimb muscle tone suppression to be 22.8 m/s. In the medial medulla, 238 reticulospinal units, which send axons to the L1 level of the spinal cord, were identified. Pontine stimulation that suppressed hindlimb muscle tone increased the firing rate of 138 units (type I). Sixteen type I units showed a delayed response to the pontine stimulation with a latency of 10 ms or longer (type Id), whereas 122 type I units exhibited an earlier response (type Ie). Seven type Ie units had an axonal conduction velocity of <22.8 m/s, whereas the remaining 115 conducted at faster than 22.8 m/s. Early and late hindlimb muscle tone suppressions were hypothesized to be mediated through fast and slow conducting type Ie reticulospinal units. The activity of type Id neurons may contribute to the cessation of the early-phase suppression as well as to the induction, maintenance, or cessation of the late-phase suppression.

Drop episodes in Coffin-Lowry syndrome: exaggerated startle responses treated with clonazepam

A 16-year-old girl had fully manifested Coffin-Lowry syndrome and drop episodes. Her drop episodes were precipitated by sudden unexpected tactile or auditory stimuli associated with the electrostatic circumstances in her leg muscles immediately after the stimuli. Studies revealed that her drop episode symptom was an unusual type of startle response and that it may be associated with Coffin-Lowry syndrome.

[Phasic activity of REM sleep in newborns and infants and its relationship with apnea episodes]

When the apnea hypothesis turned to be an explanation for sudden infant death syndrome (SIDS) many authors tried to find if near-miss or apparent life-threatening events (ALTE) could be markers of SIDS. It was suggested that phasic REM activity is associated with increased respiratory neuron activity and prevents prolonged apnea in near-miss SIDS. In a previous retrospective study with newborns we did not confirm these results, nevertheless we had several babies with serious neurological disturbances. The aim of this study was to verify the relationship of phasic activity (rapid eyes movement and sucking bursts) with both apneic and non-apneic epochs during REM sleep. We studied 86 children referred for evaluation because they presented an ALTE during sleep or apneas. The subjects were divided in three groups by age (newborns, n = 31; 1-6 months, n = 48; and > 6 < 12 months, n = 7). They were all submitted to a clinical and neurological evaluation in order to detect possible etiological factors to the apneic episode. The polysomnograms (PS) consisted of EEG, submental EMG, electro-oculogram and cardiorespiratory monitoring. The records were made between 11 am and 15 pm for 2 or 3 hours. The electrodes were disposed in the 10-20 system. During one five-minutes epoch of REM sleep we verified the incidence of phasic activity (rapid eyes movement or sucking bursts) time locked to apneic episodes and compared with a similar duration non-apneic epoch. To evaluate the relationship of phasic activity with apneic and non-apneic eopchs we compared the incidence of rapid eyes movements and sucking bursts in each group. Our results showed that phasic activity of REM sleep (sucking bursts) seems to be more frequent in newborns in non-apneic epochs (p < 0.05). Between 1-6 months the number of rapid eyes movements were more frequent in non-apneic epochs (p = 0.001). In conclusion our findings suggest that phasic activity of REM sleep seems to be more evident in nonapneic epochs during the first six months of life. Although central apneas may have their origin in an intrinsic disturb of the respiratory control center they may be influenced by the phasic activity of REM sleep. The rapid eyes movements and sucking bursts may have a protection effect against apneas at least in the first 6 months of life. which is the predominant period for SIDS. We suggest that the excitatory driving related to generation of phasic activity in REM sleep may block or atenuate tonic inhibition of respiratory motoneuron and avoid apnea. It is still open for discussion the possible relation between failure of this protective mechanism and SIDS.

Maturation of motility and motor inhibition in rapid-eye-movement sleep

OBJECTIVE

To describe the age-related changes in the number of movements in rapid eye movement (REM) sleep, and to quantify the functional maturation of motor inhibition.

STUDY DESIGN

Gross movements, phasic mentalis muscle activity (PMMA), and a new index that expressed the shortness of PMMA (the proportion of short PMMA among all PMMA) were examined cross-sectionally in 87 healthy children from premature babies to preadolescents by means of a single (all-night) polysomnography.

RESULTS

The incidence of gross movements and long PMMA decreased with age, whereas that of short PMMA increased with age. The new index exhibited an age-related increase, with the highest correlation with age among sleep parameters examined, and reached an adult level after 6 years of age.

CONCLUSION

We found that the age-related reduction of PMMA duration, which was expressed by a new index, occurred in parallel with the maturation of the inhibitory system that is tonically activated during REM sleep. We named this index the tonic inhibition index and concluded that the neuronal system involved in motor inhibition during REM sleep was still maturing during early childhood. We propose the tonic inhibition index as a useful quantitative indicator for the maturity of the inhibitory system.

A quantitative assessment of the maturation of phasic motor inhibition during REM sleep

During rapid eye movement (REM) sleep, phasic and further motor inhibition occurs during clusters of REMs besides tonic motor inhibition. We describe the age-related quantitative change of the activity of this REM-related phasic motor inhibition. For this purpose, we introduced the phasic inhibition index (PII). PII is the rate of simultaneous occurrence of bursts of horizontal REMs and phasic mentalis muscle activity during REM sleep. We examined these phasic REM sleep parameters in 87 healthy children from premature babies to preadolescents. The incidence of bursts of REMs showed no age-related change, while that of the phasic mentalis muscle activity increased with age. The simple ratio between the incidence of bursts of REMs and that of phasic mentalis muscle activity showed no significant age-related change, whereas PII decreased rapidly during infancy and reached low constant values thereafter. We concluded that this age-related PII decline reflected the maturation of REM-related phasic motor inhibition. This is the first quantitative description on the development of human motor inhibition. Taken with the neuronal basis underlying REM-related phasic motor inhibition, we hypothesize that a PII value is within the normal low range as far as both the rostral pontine tegmentum and the brainstem inhibitory pathways are functionally intact.

Phasic motor activity reduction occurring with horizontal rapid eye movements during REM sleep is disturbed in infantile spasms

Single polysomnography was performed before treatment in 17 patients with infantile spasms (IS) (13 with a cryptogenic type and 4 with a symptomatic one). Their sleep components during rapid eye movement (REM) sleep were compared with those in 22 age-matched controls. The tonic muscle atonia during REM sleep was observed in all IS patients as in controls. The amount of REM sleep in IS patients was significantly lower, while the incidences of gross movements, phasic chin muscle activity, and bursts of horizontal rapid eye movements were identical with those in controls. The phasic inhibition index (PII), i.e., the rate of simultaneous occurrence of phasic chin muscle activity and bursts of horizontal rapid eye movements, was significantly higher in IS than in controls. The PII value was the only parameter that reflected our patients' prognosis among the obtained REM sleep parameters. We presume that the elevated PII in IS reflects the weakness of the phasic motor activity reduction occurring with horizontal rapid eye movements, and attribute this disturbance to a functional instability of the rostral pontine tegmentum. We propose that PII is a useful parameter for assessing the prognosis of IS. Considering the neural basis for elevated PII in IS, this index is expected to provide a clue for explaining the pathophysiology of IS.