Spontaneous activity


Close your eyes, cover your ears, and do not touch anything. Even without any active afferent stimuli coming to the sensory areas, the brain is known to display a spontaneous activity whose nature and origin is still a matter of debate. Whatever the time is, your brain is constantly active and millions of neurons are emitting action potentials every millisecond. If not, this is a clear clinical sign that you are dead. This spontaneous activity, also called ongoing activity, is by definition the running activity of the brain when not ``facing" or processing particular stimuli. This is somehow the resting state of the brain, when no particular or at least no known actions are performed. The nature of this activity is correlated with behavioural states, being different during awake states and sleep. Its nature can be captured at different scales, depending on the device used to record it. For example with electro-or magneto encephalography (EEG or MEG), the frequency content of large scale brain electrical activity can be used to asses and characterize different cortical states of activity. It is usually divided into frequency bands: rhythm, with frequencies around 8-12 Hz, can be seen as an awake resting state, when eyes are closed. rhythm (10-30 Hz) is a kind of normal working state. oscillations, at more than 30 Hz appear during cross-modal tasks, active and intense concentration and memory tasks (in addition to slow oscillations observed in the EEG signal, such as (4Hz) and (4-10 Hz)).

Origin of Spontaneous activity

The origin of this spontaneous activity in the cortex is far from being clearly understood. Isolated neurons by themselves seem to have some homeostatic processes making them able to be spontaneously active, even if no incoming activity is present. This phenomenon has also been reported in cortical neurons [Llinas1991, Mazzoni2007], either taken in vitro brain slices [Timofeev2000] or in cultures [Gross1982]. Such activity, once created, can easily reverberate and be amplified in the microcircuits made by the neuronal connections, and lead to a self-sustained activity regime. How long this ongoing activity will last depends on the preparation, on the size of the network, and some other unknown parameters. Plasticity, the fact that the efficacy transmission of the synapses is not constant over time, the fact that neurons may be dying during the time of the in vitro preparation: all affect this activity, and progressively silence the network. Nevertheless, even an isolated brain displays such a spontaneous activity, i.e. the brain does not require external inputs to generate its own recurrent activity.

To focus on the sensory systems in vivo, the origins of ongoing activity are already found in the transduction layers, where the external world is transformed into electrical activities that are relayed to the cortex. The resting state of the brain is then an active one, and relevant information need to be extracted from these continuous and ongoing flows of sensory inputs. To illustrate this, one can look at recent data from techniques that allow to record more and more accurately the detailed and exact ongoing activity in awake animals. In Figure nearby adapted from [Lin2006], one can see the spiking activity in an awake mouse, and the subtle difference when the animal receives a clear external stimulation (red line). More than 250 neurons are recorded in parallel with a multi-electrode array. Understanding how pertinent information is extracted from this ongoing activity is a crucial step.



Left: spontaneous spiking activity, as a raster plot, for 285 neurons recorded in awake behaving mouse. Stimulation time (a puff of air is made on the leg of the animal) is indicated by a red line. Right: picture of the device.



Adapted from (Lin et al, 2006). Left: spontaneous spiking activity, as a raster plot, for 285 neurons recorded in awake behaving mouse. Stimulation time (a puff of air is made on the leg of the animal) is indicated by a red line. Right: picture of the device.


Intracellular recording of the membrane potential of a cat V1 neuron in spontaneous activity, under anesthesia. Data from Fregnac's lab. The irregularity of the discharge can be observed (and same with the spikes), and the small fluctuations of the membrane potential reflect the ongoing synaptic bombardment..

Nature of the spontaneous activity

The exact nature of the spontaneous activity is hard to capture, for several reasons. The first one is that the dynamical nature of this resting state is not that clear, and the question of its stationarity remains open. Imaging tools available nowadays (from intracellular recordings to local field potentials (LFP), voltage-sensitive dyes (VSD), two-photons) can give an insight about its nature, but not a full and exhaustive view of the electrical activity over large portions of the brain.

Age, wakefulness and anaesthetic dependence: statistics of this spontaneous activity recorded in vivo depend on the age and the state of the animal. Anaesthetics are known to perturb the balance between excitation and inhibition [Winters1976], leading to pathological activity that may be sometimes far from the awake regime. More and more efforts are devoted to developing awake recordings that will be as precise and controlled as in the anaesthetized context [Lin2006, Ferezou2006, Greenberg2008], to draw a better picture of the brain's activity. An observation that can be made from these awake recordings is that ongoing activity is rather sparse and neurons fire spontaneously at relatively low firing rates. Again the situation varies as a function of the age, the area, the species, and is used the anaesthetic, but in freely moving awake rats, sparse activity was observed intra-cellularly [Lee2006].

Slow Oscillations: In spontaneous activity under anaesthesia, slow oscillations observed (in the EEG but also in the membrane potential of individual neurons [Steriade1993a, Steriade1993]) have been considered as reflecting a switch between "up" and "down" states. In the membrane potential trace recorded in vivo, one observes some silent periods, where the membrane stays close to its resting potential (``down” state), and some very active periods where the membrane is strongly depolarized and the neuron sustains a strong irregular spiking activity (``up” state).

Irregularity: Oscillatory or not, it has been observed that the spiking activity of neurons in vivo is rather sparse and highly irregular. Most V1 neurons for example display Poissonian or supra-Poisson spike count variability in response to low dimensional stimuli such as bars and gratings [Dean1981]. This and other experimental data are in favour of the synchronous or asynchronous irregular regimes explained in the Balanced Network Section: neurons fire as Poisson sources, irregularly, with a coefficient of variation for their inter-spike intervals close to 1 [Nawrot2008]. The origin of this irregular activity observed in the sub-threshold voltage and/or in spiking activity is linked to synaptic activity [Pare1998, Destexhe1999]. To illustrate the irregularity, one can see on the left the membrane potential of a cat V1 neuron in absence of stimulation (data taken from Frégnac's lab). As we can see, the cell is spontaneously firing action potentials, and its membrane potential is fluctuating, as indirect evidence of the synaptic bombardment received by the neuron.



[Llinas1991] R. R. Llinás, A. A. Grace, and Y. Yarom, "In vitro neurons in mammalian cortical layer 4 exhibit intrinsic oscillatory activity in the 10- to 50-Hz frequency range.," Proceedings of the national academy of sciences of the united states of america, vol. 88, iss. 3, pp. 897-901, 1991.
abstract = {We report here the presence of fast subthreshold oscillatory potentials recorded in vitro from neurons within layer 4 of the guinea pig frontal cortex. Two types of oscillatory neurons were recorded: (i) One type exhibited subthreshold oscillations whose frequency increased with membrane depolarization and encompassed a range of 10-45 Hz. Action potentials in this type of neuron demonstrated clear after-hyperpolarizations. (ii) The second type of neuron was characterized by narrow-frequency oscillations near 35-50 Hz. These oscillations often outlasted the initiating depolarizing stimulus. No calcium component could be identified in their action potential. In both types of cell the subthreshold oscillations were tetrodotoxin-sensitive, indicating that the depolarizing phase of the oscillation was generated by a voltage-dependent sodium conductance. The initial depolarizing phase was followed by a potassium conductance responsible for the falling phase of the oscillatory wave. In both types of cell, the subthreshold oscillation could trigger spikes at the oscillatory frequency, if the membrane was sufficiently depolarized. Combining intracellular recordings with Lucifer yellow staining showed that the narrow-frequency oscillatory activity was produced by a sparsely spinous interneuron located in layer 4 of the cortex. This neuron has extensive local axonal collaterals that ramify in layers 3 and 4 such that they may contribute to the columnar synchronization of activity in the 40- to 50-Hz range. Cortical activity in this frequency range has been proposed as the basis for the "conjunctive properties" of central nervous system networks.},
author = {Llin\'{a}s, R R and Grace, A A and Yarom, Y},
file = {:home/pierre/Mendeley/Llin\'{a}s, Grace, Yarom - 1991.pdf:pdf},
issn = {0027-8424},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
keywords = {Animals,Cerebral Cortex,Cerebral Cortex: physiology,Electric Conductivity,Electrophysiology,Electrophysiology: methods,Guinea Pigs,Neurons,Neurons: physiology,Oscillometry},
month = feb,
number = {3},
pages = {897--901},
pmid = {1992481},
title = {{In vitro neurons in mammalian cortical layer 4 exhibit intrinsic oscillatory activity in the 10- to 50-Hz frequency range.}},
url = {http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=50921\&tool=pmcentrez\&rendertype=abstract},
volume = {88},
year = {1991}
[Mazzoni2007] [doi] A. Mazzoni, F. D. Broccard, E. Garcia-Perez, P. Bonifazi, M. E. Ruaro, and V. Torre, "On the dynamics of the spontaneous activity in neuronal networks.," Plos one, vol. 2, iss. 5, p. e439, 2007.
abstract = {Most neuronal networks, even in the absence of external stimuli, produce spontaneous bursts of spikes separated by periods of reduced activity. The origin and functional role of these neuronal events are still unclear. The present work shows that the spontaneous activity of two very different networks, intact leech ganglia and dissociated cultures of rat hippocampal neurons, share several features. Indeed, in both networks: i) the inter-spike intervals distribution of the spontaneous firing of single neurons is either regular or periodic or bursting, with the fraction of bursting neurons depending on the network activity; ii) bursts of spontaneous spikes have the same broad distributions of size and duration; iii) the degree of correlated activity increases with the bin width, and the power spectrum of the network firing rate has a 1/f behavior at low frequencies, indicating the existence of long-range temporal correlations; iv) the activity of excitatory synaptic pathways mediated by NMDA receptors is necessary for the onset of the long-range correlations and for the presence of large bursts; v) blockage of inhibitory synaptic pathways mediated by GABA(A) receptors causes instead an increase in the correlation among neurons and leads to a burst distribution composed only of very small and very large bursts. These results suggest that the spontaneous electrical activity in neuronal networks with different architectures and functions can have very similar properties and common dynamics.},
author = {Mazzoni, Alberto and Broccard, Fr\'{e}d\'{e}ric D and Garcia-Perez, Elizabeth and Bonifazi, Paolo and Ruaro, Maria Elisabetta and Torre, Vincent},
doi = {10.1371/journal.pone.0000439},
file = {:home/pierre/Mendeley/Mazzoni et al. - 2007.pdf:pdf},
issn = {1932-6203},
journal = {PloS one},
keywords = {Action Potentials,Animals,Hippocampus,Hippocampus: cytology,Hippocampus: physiology,Nerve Net,Neurons,Neurons: cytology,Rats,Rats, Wistar},
month = jan,
number = {5},
pages = {e439},
pmid = {17502919},
title = {{On the dynamics of the spontaneous activity in neuronal networks.}},
url = {http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1857824\&tool=pmcentrez\&rendertype=abstract},
volume = {2},
year = {2007}
[Timofeev2000] I. Timofeev, F. Grenier, M. Bazhenov, T. J. Sejnowski, and M. Steriade, "Origin of slow cortical oscillations in deafferented cortical slabs.," Cereb cortex, vol. 10, pp. 1185-1199, 2000.
abstract = {An in vivo preparation has been developed to study the mechanisms underlying spontaneous sleep oscillations. Dual and triple simultaneous intracellular recordings were made from neurons in small isolated cortical slabs (10 mm x 6 mm) in anesthetized cats. Spontaneously occurring slow sleep oscillations, present in the adjacent intact cortex, were absent in small slabs. However, the isolated slabs displayed brief active periods separated by long periods of silence, up to 60 s in duration. During these silent periods, 60$\backslash$\% of neurons showed non-linear amplification of low-amplitude depolarizing activity. Nearly 40$\backslash$\% of the cells, twice as many as in intact cortex, were classified as intrinsically bursting. In cortical network models based on Hodgkin-Huxley-like neurons, the summation of simulated spontaneous miniature excitatory postsynaptic potentials was sufficient to activate a persistent sodium current, initiating action potentials in single neurons that then spread through the network. Consistent with this model, enlarging the isolated cortical territory to an isolated gyrus (30 mm x 20 mm) increased the probability of initiating large-scale activity. In these larger territories, both the frequency and regularity of the slow oscillation approached that generated in intact cortex. The frequency of active periods in an analytical model of the cortical network accurately predicted the scaling observed in simulations and from recordings in cortical slabs of increasing size.},
author = {Timofeev, I and Grenier, F and Bazhenov, M and Sejnowski, T J and Steriade, M},
file = {:home/pierre/Mendeley/Timofeev et al. - 2000.pdf:pdf},
journal = {Cereb Cortex},
keywords = {Animals; Cats; Cerebral Cortex; Denervation; Elect,Neurological; Nerve Net; Neurons; Oscillometry; Th},
pages = {1185--1199},
pmid = {11073868},
title = {{Origin of slow cortical oscillations in deafferented cortical slabs.}},
volume = {10},
year = {2000}
[Gross1982] G. W. Gross, N. a Williams, and J. H. Lucas, "Recording of spontaneous activity with photoetched microelectrode surfaces from mouse spinal neurons in culture.," Journal of neuroscience methods, vol. 5, iss. 1-2, pp. 13-22, 1982.
abstract = {A matrix of photoetched gold conductors integrated into the floor of a tissue culture chamber has been used to record from mammalian spinal cord neurons grown on the insulation layer of the multielectrode plate. Spontaneous activity has been monitored from tissue microfragments less than 150 micrometers in diameter and from thin sheets of spinal cell aggregates. Maximum spike amplitudes of 360 microV with signal-to-noise ratios of 8:1 have so far been achieved and the spontaneous activity maintained for several days. Recording electrode impedances measured between 4 and 7 M omega at 1 kHz. Conductor tips were deinsulated with laser pulses that formed shallow craters 2 micrometers deep and 12 micrometers in diameter. Addition of colloidal gold or platimum black was not necessary to achieve satisfactory recordings.},
author = {Gross, G W and Williams, a N and Lucas, J H},
file = {:home/pierre/Mendeley/Gross, Williams, Lucas - 1982.pdf:pdf},
issn = {0165-0270},
journal = {Journal of neuroscience methods},
keywords = {Animals,Culture Techniques,Membrane Potentials,Mice,Microelectrodes,Neurons,Neurons: physiology,Neurophysiology,Neurophysiology: instrumentation,Spinal Cord,Spinal Cord: cytology},
month = jan,
number = {1-2},
pages = {13--22},
pmid = {7057675},
title = {{Recording of spontaneous activity with photoetched microelectrode surfaces from mouse spinal neurons in culture.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/7057675},
volume = {5},
year = {1982}
[Lin2006] [doi] L. Lin, G. Chen, K. Xie, K. A. Zaia, S. Zhang, and J. Z. Tsien, "Large-scale neural ensemble recording in the brains of freely behaving mice.," Journal of neuroscience methods, vol. 155, iss. 1, pp. 28-38, 2006.
abstract = {With the availability of sophisticated genetic techniques, the mouse is a valuable mammalian model to study the molecular and cellular basis of cognitive behaviors. However, the small size of mice makes it difficult for a systematic investigation of activity patterns of neural networks in vivo. Here we report the development and construction of a high-density ensemble recording array with up to 128-recording channels that can be formatted as single electrodes, stereotrodes, or tetrodes. This high-density recording array is capable of recording from hundreds of individual neurons simultaneously in the hippocampus of the freely behaving mice. This large-scale in vivo ensemble recording techniques, once coupled with mouse genetics, should be valuable to the study of complex relationship between the genes, neural network, and cognitive behaviors.},
author = {Lin, Longnian and Chen, Guifen and Xie, Kun and Zaia, Kimberly A and Zhang, Shuqing and Tsien, Joe Z},
doi = {10.1016/j.jneumeth.2005.12.032},
issn = {0165-0270},
journal = {Journal of neuroscience methods},
keywords = {Action Potentials,Action Potentials: physiology,Animals,Behavior, Animal,Behavior, Animal: physiology,Electrodes, Implanted,Electrodes, Implanted: standards,Electrophysiology,Electrophysiology: instrumentation,Electrophysiology: methods,Hippocampus,Hippocampus: physiology,Mice,Microelectrodes,Microelectrodes: standards,Movement,Movement: physiology,Nerve Net,Nerve Net: physiology,Neural Pathways,Neural Pathways: physiology,Neurophysiology,Neurophysiology: instrumentation,Neurophysiology: methods,Pyramidal Cells,Pyramidal Cells: physiology,Signal Processing, Computer-Assisted,Signal Processing, Computer-Assisted: instrumentat},
month = jul,
number = {1},
pages = {28--38},
pmid = {16554093},
title = {{Large-scale neural ensemble recording in the brains of freely behaving mice.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/16554093},
volume = {155},
year = {2006}
[Winters1976] [doi] W. D. Winters, "Effects of drugs on the electrical activity of the brain: anesthetics.," Annual review of pharmacology and toxicology, vol. 16, pp. 413-26, 1976.
abstract = {The major concepts presented in this review can be summarized as follows: 1. There is a multidirectional continuum of anesthetic states--some represented by CNS excitation and others by depression. 2. The reticular activating system is influenced by all anesthetics; some inhibit its action (stage III) and some hyperexcite the system resulting in a function disorganization (stage II-C). 3. Some agents traverse both excitation and depression, diethyl ether (I, II, III). 4. Others induce only stage II--catalepsia, e.g. nitrous oxide, ketamine, gamma-hydroxybutyrate, alpha-chloralose, phencyclidine, trichlorethylene, and enflurane. 5. Others induce no stage II but progress directly from stage I stage III, e.g. halothane and barbiturates. 6. Cataleptic agents may induce further CNS excitation manifested by seizures, e.g. gamma-hydroxybutyrate, phencyclidine, ketamine, alpha-chloralose, trichlorethylene, and enflurane. 7. The functional definition of surgical anesthesia is: a stage induced by a drug that makes the subject relatively unresponsive to painful stimuli and amnestic. Thus, the subject does not respond during surgery and cannot recall what happened afterwards. This state can be achieved by functional disruption of CNS systems by marked stimulation or depression.},
author = {Winters, W D},
doi = {10.1146/annurev.pa.16.040176.002213},
issn = {0362-1642},
journal = {Annual review of pharmacology and toxicology},
keywords = {Acoustic Stimulation,Anesthetics,Anesthetics: classification,Anesthetics: pharmacology,Animals,Brain,Brain: drug effects,Cats,Electroencephalography,Electrophysiology,Evoked Potentials,Evoked Potentials: drug effects,Humans,Reticular Formation,Reticular Formation: drug effects},
month = jan,
pages = {413--26},
pmid = {779620},
title = {{Effects of drugs on the electrical activity of the brain: anesthetics.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/779620},
volume = {16},
year = {1976}
[Ferezou2006] [doi] I. Ferezou, S. Bolea, and C. C. H. Petersen, "Visualizing the cortical representation of whisker touch: voltage-sensitive dye imaging in freely moving mice.," Neuron, vol. 50, iss. 4, pp. 617-29, 2006.
abstract = {Voltage-sensitive dye imaging resolves the spatiotemporal dynamics of supragranular subthreshold cortical activity with millisecond temporal resolution and subcolumnar spatial resolution. We used a flexible fiber optic image bundle to visualize voltage-sensitive dye dynamics in the barrel cortex of freely moving mice while simultaneously filming whisker-related behavior to generate two movies matched frame-by-frame with a temporal resolution of up to 2 ms. Sensory responses evoked by passive whisker stimulation lasted longer and spread further across the barrel cortex in awake mice compared to anesthetized mice. Passively evoked sensory responses were large during behaviorally quiet periods and small during active whisking. However, as an exploring mouse approached an object while whisking, large-amplitude, propagating cortical sensory activity was evoked by active whisker-touch. These experiments demonstrate that fiber optics can be used to image cortical sensory activity with high resolution in freely moving animals. The results demonstrate differential processing of sensory input depending upon behavior.},
author = {Ferezou, Isabelle and Bolea, Sonia and Petersen, Carl C H},
doi = {10.1016/j.neuron.2006.03.043},
issn = {0896-6273},
journal = {Neuron},
keywords = {Anesthesia, General,Animals,Behavior, Animal,Brain Mapping,Diagnostic Imaging,Evoked Potentials, Somatosensory,Evoked Potentials, Somatosensory: physiology,Fiber Optic Technology,Fiber Optic Technology: methods,Fluorescent Dyes,Image Processing, Computer-Assisted,Mice,Optical Fibers,Patch-Clamp Techniques,Somatosensory Cortex,Somatosensory Cortex: physiology,Vibrissae,Vibrissae: innervation,Wakefulness,Wakefulness: physiology},
month = may,
number = {4},
pages = {617--29},
pmid = {16701211},
title = {{Visualizing the cortical representation of whisker touch: voltage-sensitive dye imaging in freely moving mice.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/16701211},
volume = {50},
year = {2006}
[Greenberg2008] [doi] D. S. Greenberg, A. R. Houweling, and J. N. D. Kerr, "Population imaging of ongoing neuronal activity in the visual cortex of awake rats.," Nature neuroscience, vol. 11, iss. 7, pp. 749-51, 2008.
abstract = {It is unclear how the complex spatiotemporal organization of ongoing cortical neuronal activity recorded in anesthetized animals relates to the awake animal. We therefore used two-photon population calcium imaging in awake and subsequently anesthetized rats to follow action potential firing in populations of neurons across brain states, and examined how single neurons contributed to population activity. Firing rates and spike bursting in awake rats were higher, and pair-wise correlations were lower, compared with anesthetized rats. Anesthesia modulated population-wide synchronization and the relationship between firing rate and correlation. Overall, brain activity during wakefulness cannot be inferred using anesthesia.},
author = {Greenberg, David S and Houweling, Arthur R and Kerr, Jason N D},
doi = {10.1038/nn.2140},
issn = {1097-6256},
journal = {Nature neuroscience},
keywords = {Action Potentials,Action Potentials: physiology,Algorithms,Anesthesia,Animals,Animals, Newborn,Calcium,Calcium: metabolism,Diagnostic Imaging,Egtazic Acid,Egtazic Acid: analogs \& derivatives,Egtazic Acid: diagnostic use,Electroencephalography,Electroencephalography: methods,Neurons,Neurons: physiology,Photons,Rats,Rats, Long-Evans,Rats, Sprague-Dawley,Rhodamines,Rhodamines: diagnostic use,Spectrum Analysis,Statistics, Nonparametric,Visual Cortex,Visual Cortex: cytology,Wakefulness,Wakefulness: physiology},
month = jul,
number = {7},
pages = {749--51},
pmid = {18552841},
title = {{Population imaging of ongoing neuronal activity in the visual cortex of awake rats.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/18552841},
volume = {11},
year = {2008}
[Lee2006] [doi] A. K. Lee, I. D. Manns, B. Sakmann, and M. Brecht, "Whole-cell recordings in freely moving rats.," Neuron, vol. 51, iss. 4, pp. 399-407, 2006.
abstract = {Intracellular recording, which allows direct measurement of the membrane potential and currents of individual neurons, requires a very mechanically stable preparation and has thus been limited to in vitro and head-immobilized in vivo experiments. This restriction constitutes a major obstacle for linking cellular and synaptic physiology with animal behavior. To overcome this limitation we have developed a method for performing whole-cell recordings in freely moving rats. We constructed a miniature head-mountable recording device, with mechanical stabilization achieved by anchoring the recording pipette rigidly in place after the whole-cell configuration is established. We obtain long-duration recordings (mean of approximately 20 min, maximum 60 min) in freely moving animals that are remarkably insensitive to mechanical disturbances, then reconstruct the anatomy of the recorded cells. This head-anchored whole-cell recording technique will enable a wide range of new studies involving detailed measurement and manipulation of the physiological properties of identified cells during natural behaviors.},
author = {Lee, Albert K and Manns, Ian D and Sakmann, Bert and Brecht, Michael},
doi = {10.1016/j.neuron.2006.07.004},
file = {:home/pierre/Mendeley/Lee et al. - 2006.pdf:pdf},
issn = {0896-6273},
journal = {Neuron},
keywords = {Animal; Brain; Electrodes,Animals; Animals,Implanted; Male; Membrane Potentials; Microelectro,Newborn; Behavior,Sprague-Dawley; Rats,Wistar; Wakefulness},
month = aug,
number = {4},
pages = {399--407},
pmid = {16908406},
shorttitle = {Neuron},
title = {{Whole-cell recordings in freely moving rats.}},
url = {http://dx.doi.org/10.1016/j.neuron.2006.07.004},
volume = {51},
year = {2006}
[Steriade1993a] M. Steriade, "Central core modulation of spontaneous oscillations and sensory transmission in thalamocortical systems.," Current opinion in neurobiology, vol. 3, iss. 4, pp. 619-25, 1993.
abstract = {Central core (brainstem, diencephalic and basal forebrain) systems influence the functional modes of thalamic and cortical neurons during behavioral states of vigilance. Recent studies in vivo and in vitro have focused on the cellular properties of central core systems and their modulation of slow sleep oscillations, fast rhythms during arousal and dreaming state, and the fine inhibitory sculpturing of afferent signals.},
author = {Steriade, M},
issn = {0959-4388},
journal = {Current opinion in neurobiology},
keywords = {Animals,Arousal,Arousal: physiology,Brain,Brain Stem,Brain Stem: physiology,Brain: physiology,Cerebral Cortex,Cerebral Cortex: physiology,Diencephalon,Diencephalon: physiology,Dreams,Dreams: physiology,Humans,Models, Neurological,Neurons,Neurons: physiology,Perception,Perception: physiology,Sleep,Sleep: physiology,Synaptic Transmission,Synaptic Transmission: physiology,Thalamus,Thalamus: physiology},
month = aug,
number = {4},
pages = {619--25},
pmid = {8219730},
title = {{Central core modulation of spontaneous oscillations and sensory transmission in thalamocortical systems.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/8219730},
volume = {3},
year = {1993}
[Steriade1993] M. Steriade, D. A. McCormick, and T. J. Sejnowski, "Thalamocortical oscillations in the sleeping and aroused brain.," Science (new york, n.y.), vol. 262, iss. 5134, pp. 679-85, 1993.
abstract = {Sleep is characterized by synchronized events in billions of synaptically coupled neurons in thalamocortical systems. The activation of a series of neuromodulatory transmitter systems during awakening blocks low-frequency oscillations, induces fast rhythms, and allows the brain to recover full responsiveness. Analysis of cortical and thalamic networks at many levels, from molecules to single neurons to large neuronal assemblies, with a variety of techniques, ranging from intracellular recordings in vivo and in vitro to computer simulations, is beginning to yield insights into the mechanisms of the generation, modulation, and function of brain oscillations.},
author = {Steriade, M and McCormick, D A and Sejnowski, T J},
issn = {0036-8075},
journal = {Science (New York, N.Y.)},
keywords = {Animals,Arousal,Arousal: physiology,Cerebral Cortex,Cerebral Cortex: physiology,Electroencephalography,Sleep,Sleep: physiology,Thalamus,Thalamus: physiology},
month = oct,
number = {5134},
pages = {679--85},
pmid = {8235588},
title = {{Thalamocortical oscillations in the sleeping and aroused brain.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/8235588},
volume = {262},
year = {1993}
[Dean1981] A. F. Dean, "The relationship between response amplitude and contrast for cat striate cortical neurones.," The journal of physiology, vol. 318, pp. 413-427, 1981.
abstract = {1. The activity of forty-three neurones in the cat's striate cortex in response to laterally moving sinusoidal gratings of various contrasts was recorded, in order to examine the relationship between response amplitude and contrast. 2. Neurones seemed to exhibit contrast thresholds: stimuli of very low contrast failed to evoke a change in the response amplitude from the concurrent levels of spontaneous activity. 3. The suprathreshold portion of the response-contrast relation was found to be monotonic. Typically, the relation was adequately described as linear up to contrasts of about 0.3, above which, varying degrees of saturation were evident. 4. The response-contrast relation had a higher threshold and a shallower slope when the spatial frequency was not optimal for the neurone. 5. The slope, or gain, of the response-contrast relation for a stimulus of optimal orientation and spatial frequency varied considerably from neurone to neurone. The gains of special complex cells were significantly greater than those of either standard complex cells or simple cells. 6. The distributions of contrast threshold and contrast gain were examined for their dependence on optimal spatial frequency. Contrast threshold was significantly positively correlated with optimal spatial frequency, while contrast gain was significantly negatively correlated with optimal spatial frequency. This behaviour is consistent with an optical contribution to the measured response properties of striate cortical neurones.},
annote = {
From Duplicate 1 (
The relationship between response amplitude and contrast for cat striate cortical neurones.
- Dean, A F )
From Duplicate 1 (
The relationship between response amplitude and contrast for cat striate cortical neurones.
- Dean, A F )
author = {Dean, AF F},
file = {:home/pierre/Mendeley/Dean - 1981(2).pdf:pdf;:home/pierre/.local/share/data/Mendeley Ltd./Mendeley Desktop/Downloaded/Dean - 1981.pdf:pdf},
issn = {0022-3751},
journal = {The Journal of Physiology},
keywords = {Action Potentials,Animals,Cats,Form Perception,Form Perception: physiology,Neurons,Neurons: physiology,Pattern Recognition,Visual,Visual Cortex,Visual Cortex: physiology,Visual: physiology},
month = sep,
pages = {413--427},
pmid = {7320898},
title = {{The relationship between response amplitude and contrast for cat striate cortical neurones.}},
url = {http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1245500\&tool=pmcentrez\&rendertype=abstract http://jp.physoc.org/content/318/1/413.short},
volume = {318},
year = {1981}
[Nawrot2008] [doi] M. P. Nawrot, C. Boucsein, V. {Rodriguez Molina}, A. Riehle, A. Aertsen, and S. Rotter, "Measurement of variability dynamics in cortical spike trains.," Journal of neuroscience methods, vol. 169, iss. 2, pp. 374-90, 2008.
abstract = {We propose a method for the time-resolved joint analysis of two related aspects of single neuron variability, the spiking irregularity measured by the squared coefficient of variation (CV(2)) of the ISIs and the trial-by-trial variability of the spike count measured by the Fano factor (FF). We provide a calibration of both estimators using the theory of renewal processes, and verify it for spike trains recorded in vitro. Both estimators exhibit a considerable bias for short observations that count less than about 5-10 spikes on average. The practical difficulty of measuring the CV(2) in rate modulated data can be overcome by a simple procedure of spike train demodulation which was tested in numerical simulations and in real spike trains. We propose to test neuronal spike trains for deviations from the null-hypothesis FF=CV(2). We show that cortical pyramidal neurons, recorded under controlled stationary input conditions in vitro, comply with this assumption. Performing a time-resolved joint analysis of CV(2) and FF of a single unit recording from the motor cortex of a behaving monkey we demonstrate how the dynamic change of their quantitative relation can be interpreted with respect to neuron intrinsic and extrinsic factors that influence cortical variability in vivo. Finally, we discuss the effect of several additional factors such as serial interval correlation and refractory period on the empiric relation of FF and CV(2).},
author = {Nawrot, Martin P and Boucsein, Clemens and {Rodriguez Molina}, Victor and Riehle, Alexa and Aertsen, Ad and Rotter, Stefan},
doi = {10.1016/j.jneumeth.2007.10.013},
issn = {0165-0270},
journal = {Journal of neuroscience methods},
keywords = {Algorithms,Animals,Calibration,Cerebral Cortex,Cerebral Cortex: physiology,Electroencephalography,Electrophysiology,Excitatory Postsynaptic Potentials,Excitatory Postsynaptic Potentials: physiology,Haplorhini,Motor Cortex,Motor Cortex: physiology,Neurons,Neurons: physiology,Poisson Distribution,Pyramidal Cells,Pyramidal Cells: physiology,Rats,Rats, Long-Evans,Refractory Period, Electrophysiological,Refractory Period, Electrophysiological: physiolog,Stochastic Processes,Synapses,Synapses: physiology},
month = apr,
number = {2},
pages = {374--90},
pmid = {18155774},
title = {{Measurement of variability dynamics in cortical spike trains.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/18155774},
volume = {169},
year = {2008}
[Pare1998] D. Paré, E. Shink, H. Gaudreau, A. Destexhe, and E. J. Lang, "Impact of spontaneous synaptic activity on the resting properties of cat neocortical pyramidal neurons In vivo.," Journal of neurophysiology, vol. 79, iss. 3, pp. 1450-60, 1998.
abstract = {The frequency of spontaneous synaptic events in vitro is probably lower than in vivo because of the reduced synaptic connectivity present in cortical slices and the lower temperature used during in vitro experiments. Because this reduction in background synaptic activity could modify the integrative properties of cortical neurons, we compared the impact of spontaneous synaptic events on the resting properties of intracellularly recorded pyramidal neurons in vivo and in vitro by blocking synaptic transmission with tetrodotoxin (TTX). The amount of synaptic activity was much lower in brain slices (at 34 degrees C), as the standard deviation of the intracellular signal was 10-17 times lower in vitro than in vivo. Input resistances (Rins) measured in vivo during relatively quiescent epochs ("control Rins") could be reduced by up to 70\% during periods of intense spontaneous activity. Further, the control Rins were increased by approximately 30-70\% after TTX application in vivo, approaching in vitro values. In contrast, TTX produced negligible Rin changes in vitro (approximately 4\%). These results indicate that, compared with the in vitro situation, the background synaptic activity present in intact networks dramatically reduces the electrical compactness of cortical neurons and modifies their integrative properties. The impact of the spontaneous synaptic bombardment should be taken into account when extrapolating in vitro findings to the intact brain.},
author = {Par\'{e}, D and Shink, E and Gaudreau, H and Destexhe, A and Lang, E J},
issn = {0022-3077},
journal = {Journal of neurophysiology},
keywords = {Animals,Brain,Brain: physiology,Cats,Electroencephalography,Guinea Pigs,Membrane Potentials,Membrane Potentials: physiology,Neocortex,Neocortex: drug effects,Neocortex: physiology,Nerve Net,Nerve Net: physiology,Pyramidal Cells,Pyramidal Cells: physiology,Reaction Time,Synapses,Synapses: drug effects,Synapses: physiology,Tetrodotoxin,Tetrodotoxin: pharmacology},
month = mar,
number = {3},
pages = {1450--60},
pmid = {9497424},
title = {{Impact of spontaneous synaptic activity on the resting properties of cat neocortical pyramidal neurons In vivo.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/9497424},
volume = {79},
year = {1998}
[Destexhe1999] A. Destexhe and D. Paré, "Impact of network activity on the integrative properties of neocortical pyramidal neurons in vivo.," Journal of neurophysiology, vol. 81, iss. 4, pp. 1531-47, 1999.
abstract = {During wakefulness, neocortical neurons are subjected to an intense synaptic bombardment. To assess the consequences of this background activity for the integrative properties of pyramidal neurons, we constrained biophysical models with in vivo intracellular data obtained in anesthetized cats during periods of intense network activity similar to that observed in the waking state. In pyramidal cells of the parietal cortex (area 5-7), synaptic activity was responsible for an approximately fivefold decrease in input resistance (Rin), a more depolarized membrane potential (Vm), and a marked increase in the amplitude of Vm fluctuations, as determined by comparing the same cells before and after microperfusion of tetrodotoxin (TTX). The model was constrained by measurements of Rin, by the average value and standard deviation of the Vm measured from epochs of intense synaptic activity recorded with KAc or KCl-filled pipettes as well as the values measured in the same cells after TTX. To reproduce all experimental results, the simulated synaptic activity had to be of relatively high frequency (1-5 Hz) at excitatory and inhibitory synapses. In addition, synaptic inputs had to be significantly correlated (correlation coefficient approximately 0.1) to reproduce the amplitude of Vm fluctuations recorded experimentally. The presence of voltage-dependent K+ currents, estimated from current-voltage relations after TTX, affected these parameters by <10\%. The model predicts that the conductance due to synaptic activity is 7-30 times larger than the somatic leak conductance to be consistent with the approximately fivefold change in Rin. The impact of this massive increase in conductance on dendritic attenuation was investigated for passive neurons and neurons with voltage-dependent Na+/K+ currents in soma and dendrites. In passive neurons, correlated synaptic bombardment had a major influence on dendritic attenuation. The electrotonic attenuation of simulated synaptic inputs was enhanced greatly in the presence of synaptic bombardment, with distal synapses having minimal effects at the soma. Similarly, in the presence of dendritic voltage-dependent currents, the convergence of hundreds of synaptic inputs was required to evoke action potentials reliably. In this case, however, dendritic voltage-dependent currents minimized the variability due to input location, with distal apical synapses being as effective as synapses on basal dendrites. In conclusion, this combination of intracellular and computational data suggests that, during low-amplitude fast electroencephalographic activity, neocortical neurons are bombarded continuously by correlated synaptic inputs at high frequency, which significantly affect their integrative properties. A series of predictions are suggested to test this model.},
author = {Destexhe, A and Par\'{e}, D},
issn = {0022-3077},
journal = {Journal of neurophysiology},
keywords = {Action Potentials,Action Potentials: drug effects,Action Potentials: physiology,Adrenergic alpha-Agonists,Adrenergic alpha-Agonists: pharmacology,Animals,Awareness,Awareness: physiology,Cats,Dendrites,Dendrites: drug effects,Dendrites: physiology,Electric Conductivity,Electroencephalography,Excitatory Amino Acid Antagonists,Excitatory Amino Acid Antagonists: pharmacology,Excitatory Postsynaptic Potentials,Excitatory Postsynaptic Potentials: drug effects,Excitatory Postsynaptic Potentials: physiology,Ketamine,Ketamine: pharmacology,Neocortex,Neocortex: cytology,Neocortex: physiology,Nerve Net,Neural Pathways,Pyramidal Cells,Pyramidal Cells: physiology,Synapses,Synapses: drug effects,Synapses: physiology,Tetrodotoxin,Tetrodotoxin: pharmacology,Xylazine,Xylazine: pharmacology},
month = apr,
number = {4},
pages = {1531--47},
pmid = {10200189},
title = {{Impact of network activity on the integrative properties of neocortical pyramidal neurons in vivo.}},
url = {http://www.ncbi.nlm.nih.gov/pubmed/10200189},
volume = {81},
year = {1999}

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