An interpretation of 1/f fluctuations in neuronal spike trains during dream sleep

The mesencephalic reticular formation (MRF) neurons are regarded as contributing to the activation of the cerebral cortex. We have investigated the statistical characteristics of the single neuronal activity in the MRF of cat during two activated states: paradoxical sleep (PS) and state in which the animal is watching birds (BW). 1/f-like spectra are observed for both PS and BW states, being more pronounced for PS state. For the interpretation of these findings, we have applied the clustering Poisson process, which not only gives rise to a 1/f spectrum but also suggests a generation mechanism. The MRF neuronal activities in PS and BW are closely fitted by the clustering Poisson process, both in terms of power spectral density and counting statistics. These results strongly suggest that the activities of MRF neurons in PS and BW can be interpreted as the superpositions of randomly occurring clusters which consist of various number of impulses.     

Control of motoneuron function and muscle tone during REM sleep, REM sleep behavior disorder and cataplexy/narcolepsy

REM sleep triggers a potent suppression of postural muscle tone - i.e., REM atonia. However, motor control during REM sleep is paradoxical because overall brain activity is maximal, but motor output is minimal. The skeletal motor system remains quiescent during REM sleep because somatic motoneurons are powerfully inactivated. Determining the mechanisms triggering loss of motoneuron function during REM sleep is important because breakdown in REM sleep motor control underlies sleep disorders such as REM sleep behavior disorder (RBD) and cataplexy/narcolepsy. For example, RBD is characterized by dramatic REM motor activation resulting in dream enactment and subsequent patient injury. In contrast, cataplexy a pathognomonic symptom of narcolepsy - is caused by the involuntary onset of REM-like atonia during wakefulness. This review highlights recent work from my laboratory that examines how motoneuron function is lost during normal REM sleep and it also identifies potential biochemical mechanisms underlying abnormal motor control in both RBD and cataplexy. First, I show that both GABAB and GABAA/glycine mediated inhibition of motoneurons is required for generating REM atonia. Next, I show that impaired GABA and glycine neurotransmission triggers the cardinal features of RBD in a transgenic mouse model. Last, I show that loss of an excitatory noradrenergic drive onto motoneurons is, at least in part, responsible for the loss of postural muscle tone during cataplexy in narcoleptic mice. Together, this research indicates that multiple transmitters systems are responsible for regulating postural muscle tone during REM sleep, RBD and cataplexy.     

Interpretation of 1/f fluctuations in ion conducting membranes

The main objective of this work is to resolve some uncertainties associated with the analysis of conductance fluctuations that exhibit 1/f spectral density. To this end, we derive mathematical conditions under which a discrete summation of Lorentzian functions best approximates a strictly 1/f density over a given frequency range. The intrinsic errors associated with spectral density estimates are considered and used as a constraint to determine the smallest number of optimally chosen Lorentzians required to fit a 1/f-like spectrum in a statistically acceptable manner. The results provide criteria concerning the extent to which mechanisms generating a strictly 1/f spectra may be distinguished from those generating sums of Lorentzian spectra. It is found, in particular, that 1/f-like fluctuation spectra observed in a variety of biological and model membranes may well arise from the summation of a few Lorentzian components having appropriate amplitudes and corner frequencies. Consideration of physically realistic models of ion conductive channels indicates that 1/f-like conductance fluctuation spectra could originate naturally as a direct consequence of thermodynamic constraints upon the coefficients of Lorentzian components.     

Counting statistics of 1/f fluctuations in neuronal spike trains

The mesencephalic reticular formation (MRF) neurons are regarded as contributing to the activation of the celebral cortex. In this paper, the statistical features of single neuronal activities in MRF of cat during dream sleep are investigated; the neuronal spike train exhibits 1/f fluctuations. Counting statistics is applied to the neuronal spike train giving rise to a variance/mean curve which follows at -law. For an interpretation of these findings, the clustering Poisson process is applied which not only gives rise to at -law but also suggests a generation mechanism. The MRF neuronal activities are closely fitted by the clustering Poisson process and the underlying statistical parameters can be estimated. These findings strongly suggest that neuronal activities can be interpreted as superposition of randomly occuring clusters ( = bursts of spikes).     

Further study of soma,dendrite, and axon excitation in single neurons

The present investigation continues a previous study in which the soma-dendrite system of sensory neurons was excited by stretch deformation of the peripheral dendrite portions. Recording was done with intracellular leads which were inserted into the cell soma while the neuron was activated orthodromically or antidromically. The analysis was also extended to axon conduction. Crayfish, Procambarus alleni (Faxon) and Orconectes virilis (Hagen), were used. 1. The size and time course of action potentials recorded from the soma-dendrite complex vary greatly with the level of the cell's membrane potential. The latter can be changed over a wide range by stretch deformation which sets up a "generator potential" in the distal portions of the dendrites. If a cell is at its resting unstretched equilibrium potential, antidromic stimulation through the axon causes an impulse which normally overshoots the resting potential and decays into an afternegativity of 15 to 20 msec. duration. The postspike negativity is not followed by an appreciable hyperpolarization (positive) phase. If the membrane potential is reduced to a new steady level a postspike positivity appears and increases linearly over a depolarization range of 12 to 20 mv. in various cells. At those levels the firing threshold of the cell for orthodromic discharges is generally reached. 2. The safety factor for conduction between axon and cell soma is reduced under three unrelated conditions, (a) During the recovery period (2 to 3 msec.) immediately following an impulse which has conducted fully over the cell soma, a second impulse may be delayed, may invade the soma partially, or may be blocked completely. (b) If progressive depolarization is produced by stretch, it leads to a reduction of impulse height and eventually to complete block of antidromic soma invasion, resembling cathodal block, (c) In some cells, when the normal membrane potential is within several millivolts of the relaxed resting state, an antidromic impulse may be blocked and may set up within the soma a local potential only. The local potential can sum with a second one or it may sum with potential changes set up in the dendrites, leading to complete invasion of the soma. Such antidromic invasion block can always be relieved by appropriate stretch which shifts the membrane potential out of the "blocking range" nearer to the soma firing level. During the afterpositivity of an impulse in a stretched cell the membrane potential may fall below or near the blocking range. During that period another impulse may be delayed or blocked. 3. Information regarding activity and conduction in dendrites has been obtained indirectly, mainly by analyzing the generator action under various conditions of stretch. The following conclusions have been reached: The large dendrite branches have similar properties to the cell body from which they arise and carry the same kind of impulses. In the finer distal filaments of even lightly depolarized dendrites, however, no axon type all-or-none conduction occurs since the generator potential persists to a varying degree during antidromic invasion of the cell. With the membrane potential at its resting level the dendrite terminals contribute to the prolonged impulse afternegativity of the soma. 4. Action potentials in impaled axons and in cell bodies have been compared. It is thought that normally the over-all duration of axon impulses is shorter. Local activity during reduction of the safety margin for conduction was studied. 5. An analysis was made of high frequency grouped discharges which occasionally arise in cells. They differ in many essential aspects from the regular discharges set up by the generator action. It is proposed that grouped discharges occur only when invasion of dendrites is not synchronous, due to a delay in excitation spread between soma and dendrites. Each impulse in a group is assumed to be caused by an impulse in at least one of the large dendrite branches. Depolarization of dendrites abolishes the grouped activity by facilitating invasion of the large dendrite branches.     

Enhancement of REM sleep during extraocular light exposure in humans

This study examined the effects on sleep of light administered to an extraocular site. A 3-h photic stimulus was applied to the popliteal region during sleep in 14 human subjects. Each subject also underwent a control stimulus condition during a separate laboratory session. The proportion of rapid eye movement (REM) sleep during the 3-h light administration session increased by an average of 31% relative to the control condition. The frequency but not the duration of REM episodes was altered during light exposure, thereby shortening the REM/non-REM (NREM) cycle length. No other sleep stages were significantly affected during light administration nor was sleep architecture altered after the light-exposure interval. These results confirm that extraocular light is transduced into a signal that is received and processed by the human central nervous system. In addition, they expand to a novel sensory modality previous findings that REM sleep can be enhanced by sensory stimulation.     

Further study on seasonal fluctuations of Egyptian soil fungi

The seasonal fluctuations of fungi were studied in 72 soil samples collected at 10-day intervals between January 1972 and December 1973. The richest periods in the fungal population were January, March and September–December 1972, and April, May, September, November and December 1973. The poorest months were consistently June and July of 1972 and 1973 and August 1973 which are all summer months. Thirty-nine genera were isolated of which Aspergillus, Penicillium, Fusarium, Mucor, Rhizopus and Humicola were of high seasonal occurrence. Seven genera were of moderate occurrence and these were Cochliobolus,Stachybotrys, Paecilomyces, Cunninghamella, Myrothecium, Chaetomium and Sepedonium. The remaining genera were of low or rare seasonal occurrence. Aspergillus showed its highest prevalence during the periods May-September 1972 and April-August 1973. Twenty-four species of Aspergillus in addition to two varieties of A. nidulans were isolated, of which A. niger, A. fumigatus, A. terreus, A. nidulans and A. sydowii were dominant. Thirty species of Penicillium were identified, of which P. notatum, P. funiculosum and P. chrysogenum were of high seasonal occurrence. Penicillium predominated during winter and spring months. Fusarium showed its highest percentage populations during the periods February, March, April, October, November and December 1972 and February, August, September, October and November 1973. Four species of Mucor were recorded of which M. racemosus was the commonest; and its highest percentage populations were recorded in November 1972; and February, March and November 1973 which are moderate temperature months. Rhizopus was represented by two species of which R. nigricans was of high seasonal occurrence. Three species of Humicola were isolated of which H. grisea was the most common.     

Selective REM sleep deprivation during daytime. II. Muscle atonia in non-REM sleep

One of the hallmarks of rapid eye movement (REM) sleep is muscle atonia. Here we report extended epochs of muscle atonia in non-REM sleep (MAN). Their extent and time course was studied in a protocol that included a baseline night, a daytime sleep episode with or without selective REM sleep deprivation, and a recovery night. The distribution of the latency to the first occurrence of MAN was bimodal with a first mode shortly after sleep onset and a second mode 40 min later. Within a non-REM sleep episode, MAN showed a U-shaped distribution with the highest values before and after REM sleep. Whereas MAN was at a constant level over consecutive 2-h intervals of nighttime sleep, MAN showed high initial values when sleep began in the morning. Selective daytime REM sleep deprivation caused an initial enhancement of MAN during recovery sleep. It is concluded that episodes of MAN may represent an REM sleep equivalent and that it may be a marker of homeostatic and circadian REM sleep regulating processes. MAN episodes may contribute to the compensation of an REM sleep deficit.     

Cutaneous vasomotion during REM sleep in the rabbit's ear, after alpha-receptor blockade

Cutaneous vasoconstriction in the rabbit's ear during REM sleep in a warm environment is not abolished by alpha-receptor blockade (phenoxybenzamine 6 mg/kg i.v.), thus confirming that the vasomotor response during REM sleep is independent of the activity of circulating catecholamines. The decrease in cardiac output during REM sleep may be responsible for the slight fall in transmural pressure which underlies cutaneous ear vasoconstriction during REM sleep.     

Effects of bromocriptine and alpha-flupenthixol on sleep in REM sleep deprived rats.

Administration of bromocriptine mesylate (5 mg/kg, i.p.), a dopamine receptor stimulant, to rats which were deprived of REM sleep for 24 hours resulted in a significant increase in wakefulness as well as significant reduction of REM sleep during the first 5 hours of EEG recording. These effects were completely abolished by pretreatment with α-flupenthixol (0.2 mg/kg, i.p.), a dopamine receptor blocker. The loss of REM sleep has not been regained during the next 25 hours of EEG recording suggesting that the stimulation of dopamine receptors reduced REM sleep without causing subsequent REM rebound. These data raise questions on the negative dopamine control of REM sleep and on the potential use of dopamine stimulants in clinical situations characterized by excessive REM or by REM sleep dysfunction (narcolepsy).     

Markov process of maintained impulse activity in central single neurons

To clarify the stochast properties of the maintained impulse activity of the central nervous system, we proposed a measure of statistical dependency on the basis of Shannon's entropy. This measure could provide the Markov properties of the neural impulse sequences, representing the necessary and sufficient condition for the statistical dependence. The order of Markov process of the sequence is determined by the conditional entropy which is derived from the joint entropy. Here the joint entropy in the case of Gaussian process is directly related with the covariance matrix which is substituted for the matrix of the serial correlation coefficients. Therefore the condition to determine the order of Markov process is obtained by the equation of the matrices of the serial correlation coefficients. The order of Markov process of the neural impulse sequences recorded from the mesencephalic reticular formation (MRF), red nucleus (RN), and lateral geniculate nucleus (LGN) neurons has been estimated. The maintained impulse activity of the MRF and RN neurons had from the 2-nd to 4-th order Markov property, while that of the LGN had no Markov property, in the consecutive impulse sequences.     

Pupillary behavior during wakefulness,non-REM sleep,and REM sleep in birds is opposite that of mammals

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