The spontaneous activity of neurones in the cat’s cerebral cortex

1976 ◽  
Vol 194 (1115) ◽  
pp. 211-223 ◽  
Keyword(s):  
Standard Deviation ◽  
Action Potentials ◽  
Quantitative Description ◽  
Primary Auditory Cortex ◽  
Geometric Standard Deviation ◽  
Quiet Sleep ◽  
Modal Interval ◽  
Spontaneous Action ◽  
Log Normal ◽  
Two Parameters

Chronically implanted microelectrodes have been used to obtain extracellular records of trains of spontaneous action potentials from 30 neurones in the cerebral cortices of 13 unrestrained cats. Recorded neurones were in or near to primary visual cortex, primary auditory cortex, and in the supra-sylvian gyrus. Records were made with animals in several different behavioural states, which included sleep with rapid eye-movements and quiet sleep, peacefully awake, and alarmed. Interval distributions derived from trains of 200 action potentials recorded in less than 80 s did not differ significantly from curves in which the probability of any interval is normally distributed about a modal interval, when plotted on a logarithmic time-axis. Thus the complete interval distributions of neurones firing faster than 2.5/s can be described by two parameters – a modal interval, and a geometric standard deviation. This quantitative description of interval distributions proved equally applicable to neurones in all three cortical areas and was valid over the whole range of behavioural states examined. It does not usually hold when the discharge frequency of a neurone is lower than 2.5 action potentials per second. An acceptable fit for a log-normal curve can then only be obtained for intervals that are shorter than about ten times the modal interval. It is pointed out that mean frequency of discharge is a measure of neural activity which is a secondary parameter, since it is dependent upon both modal interval and geometric standard deviation. Our preliminary data show that the two parameters which define the best-fit log-normal curves can vary independently with the behavioural state of the animal in a way that suggests that they may be physiologically important.

The effects of changing levels of arousal on the spontaneous activity of cortical neurones II. Relaxation and alarm

1976 ◽  
Vol 194 (1115) ◽  
pp. 239-251 ◽  
Keyword(s):  
Spontaneous Activity ◽  
Temporal Pattern ◽  
Discharge Rate ◽  
Geometric Standard Deviation ◽  
Sudden Increase ◽  
Lateral Cortex ◽  
Infrared Telescope ◽  
Modal Interval ◽  
Log Normal ◽  
Two Parameters

In a previous paper it has been shown that interval distributions derived from the activity of single cortical neurones can be described by log-normal curves. A cell’s temporal pattern of discharge can therefore be defined by the values of two parameters – a modal interval, and a geometric standard deviation (g. s. d.). It has also been shown that the values of both parameters change when an animal falls asleep. The modal interval becomes shorter, and the g. s. d. usually becomes larger. This paper deals with the effects of changes in arousal of animals which are awake; and, in particular, with the effects of the transition from relaxation to alarm. Single unit recordings have been made from neurones in the post-lateral and supra-sylvian gyri of unrestrained cats. In order to eliminate the direct effects of eye-movements, the experiments were carried out in complete darkness, and the animal was observed through an infrared telescope. Alarm was produced by the hiss of compressed air. An animal was said to be alarmed when he stood up abruptly and turned towards the source of the noise. Alarm produced a marked fall in the discharge frequency of those cells in post-lateral cortex which initially showed a low ( < 2 action potentials per second) rate of spontaneous activity. The discharge rate of the remaining neurones (whether in suprasylvian or post-lateral cortex) was unaffected by the sudden increase in arousal. But the temporal pattern of discharge of every cell was altered. The modal interval became longer when the animal was alarmed, and the g. s. d. usually became smaller. Such changes could have been predicted from a knowledge of the neural concomitants of the transition from sleep to wakefulness. These results suggest that the activity of all cortical neurones is affected by the level of arousal of the animal, and that this modulation takes the form of a continuum of possible modal intervals, and possible g.s.ds.

The effects of changing levels of arousal on the spontaneous activity of cortical neurones I. Sleep and wakefulness

1976 ◽  
Vol 194 (1115) ◽  
pp. 225-237 ◽  
Keyword(s):  
Preceding Paper ◽  
Geometric Standard Deviation ◽  
Modal Interval ◽  
Efficient Test ◽  
Single Neurones ◽  
Single Interval ◽  
Log Normal ◽  
Two Parameters ◽  
Interval Distribution ◽  
Comparative Measure

In the preceding paper (Burns & Webb 1976), it was shown that the interval distributions derived from the activity of single cortical neurones can be described by log-normal curves. This description proved satisfactory for cells in visual parietal and auditory cortex. Thus, two parameters – a modal interval and a geometric standard deviation (g. s. d.) – are sufficient to define the whole temporal pattern of discharge for neurones that fire faster than 2.5/s. The same two parameters may be used to describe the first parts of the interval distributions of cells firing less frequently. The purpose of the present paper is to find out whether the values of these two parameters vary systematically with an animal’s state of alertness. Records have therefore been made from single neurones in various parts of the cerebral cortex of unrestrained male cats, when the animals were awake and when they were sleeping. A cat was said to be asleep when he lay with his head supported by some part of the apparatus, with eyes shut, and pinnae unresponsive to laboratory noises. R. e. m. sleep was identified by jerky movements of limbs and eyes. If one records from the same neurone when the cat is awake and when he is asleep, the values of both mode and g. s. d. change with the onset of sleep. Thus either parameter will provide a comparative measure of the animal’s state of alertness. On average the modal interval shortens by a factor of three when an animal falls asleep. This coincides with an increase of 42 % in the size of the g. s. d. The geometric coefficient of variation, which is a dimensionless measure of scatter about the mode - g. c. v. = [log (g. s. d. )]/[log (modal interval)] - also showed systematic changes. On average the g. c. v. increased by a factor of 2.4 when an animal fell asleep. The animal’s state of arousal could also be assessed by examining a single train of action potentials. Interval distributions with modal intervals which are shorter than 20 ms appear to be characteristic of neural activity recorded from a sleeping cat. This rule offers an 88 % chance of successfully classifying a single interval distribution. The size of the g. c. v. can also serve as an efficient ‘test’ of arousal. If one assumes that g. c. vs larger than 0.32 are diagnostic of records taken from animals which are asleep, one’s chance of making an accurate classification is also 88 %. No similar distinction could be made between quiet and r. e. m. sleep.

scholarly journals Inferring the size distribution of volcanic ash from IASI measurements and optimal estimation

2016 ◽  
Author(s):  
Luke M. Western ◽  
Peter N. Francis ◽  
I. Matthew Watson ◽  
Shona Mackie
Keyword(s):  
Particle Size ◽  
Standard Deviation ◽  
Size Distribution ◽  
Volcanic Ash ◽  
Optimal Estimation ◽  
Geometric Standard Deviation ◽  
Using Data ◽  
Log Normal ◽  
Cloud Top Pressure ◽  
Ash Cloud

Abstract. This study demonstrates a method of retrieving the mass column loading and cloud-top pressure of a volcanic ash cloud, together with the effective radius and spread of the ash particle size distribution, as well as the cloud top pressure of any underlying water cloud, using an optimal estimation technique applied to Infrared Atmospheric Sounding Interferometer data. Two shapes of particle size distribution are considered, a log-normal and a gamma distribution. Results show that it is viable to retrieve a measure of the size distribution spread, namely the geometric standard deviation, when a log-normal distribution is assumed, whereas this is not the case for an assumed gamma distribution in terms of its effective variance. The volcanic conditions under which the method works well are discussed, as are its shortcomings. The method is applied to two volcanic eruptions: Eyjafjallajökull, Iceland using data from 6th May 2010 and Kasatochi, Alaska using data from 8th August 2008. The results show that the retrieved geometric standard deviation of these ash clouds is spatially variable, and is generally similar to what is assumed in many passive infrared remote sensing techniques. An abrupt change in the retrieved geometric standard deviation has been observed for the Eyjafjallajökull eruption along the trajectory of the ash cloud, and possible explanations for this are discussed.

The effects of sleep on neurons in isolated cerebral cortex

1979 ◽  
Vol 206 (1164) ◽  
pp. 281-291 ◽  
Keyword(s):  
Cerebral Cortex ◽  
Neural Activity ◽  
Geometric Standard Deviation ◽  
Neural Connections ◽  
Modal Interval ◽  
Isolated Cortex ◽  
Log Normal ◽  
Intact Cortex ◽  
The Brain ◽  
Unrestrained Animal

Slabs of cat parietal cortex with some 2 mm of underlying white matter were surgically isolated from the rest of the nervous system, without interference with the superficial blood supply. Wire micro-recording electrodes were inserted into the isolated cortex; bone, muscle and skin wounds were repaired and the animal allowed to recover from anaesthesia. The adequacy of surgical isolation was examined histologically 8-12 weeks after operation. Only one of the six preparations reported here showed surviving neural connections with the rest of the brain. Soon after operation, spontaneous bursts of neural activity appeared within the isolated area. These became more frequent until neural dis­charge was continuous but irregular. Our records were made from this time onwards. The interval distributions obtained from neurons within the isolated area did not differ significantly from log-normal curves. When the unrestrained animal fell asleep, there was no significant alteration in the modal interval or geometric standard deviation of interval distributions recorded from cells in isolated cortex. The interval distributions of neurons in isolated cerebral cortex resembled those of neurons in the intact cortex of an alarmed animal. It is concluded that the reduction of modal interval that is shown by neurons in intact cortex when an animal falls asleep is probably due to the neural influence of infracortical structures.

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