@article {1596, title = {Waking-sleep modulation of paroxysmal activities induced by partial cortical deafferentation.}, journal = {Cereb Cortex}, volume = {17}, year = {2007}, month = {2007 Feb}, pages = {272-83}, abstract = {

We investigated the dependency of electrical seizures produced by cortical undercut upon behavioral states of vigilance in chronically implanted cats. Experiments were performed 1-12 weeks after white matter transection. Multisite field potentials and intracellular activity were recorded from suprasylvian and marginal gyri. Paroxysmal activity developed within days and consisted of spike-wave complexes at 3-4 Hz occurring during the waking state (correlated with eye movements), being enhanced during slow-wave sleep (SWS) and blocked during rapid eye movement (REM) sleep. Prolonged hyperpolarizing events were seen not only during SWS (which is the case in normal animals) but also during both waking and REM, thus resulting in bimodal distribution of the membrane potential in all 3 natural states of vigilance. The increased synchrony of field potential activity expressed by shorter time of propagation over the cortical surface and the tendency toward generalization are ascribed to changes in intrinsic neuronal properties and potential disinhibition following cortical undercut.

}, keywords = {Adaptation, Physiological, Afferent Pathways, Animals, Brain Injuries, Cats, Cerebral Cortex, Circadian Rhythm, Cortical Synchronization, Denervation, Epilepsy, Post-Traumatic, Female, Male, Seizures, Sleep, Wakefulness}, issn = {1047-3211}, doi = {10.1093/cercor/bhj145}, author = {Nita, Dragos A and Ciss{\'e}, Youssouf and Igor Timofeev and Steriade, Mircea} } @article {1598, title = {Increased propensity to seizures after chronic cortical deafferentation in vivo.}, journal = {J Neurophysiol}, volume = {95}, year = {2006}, month = {2006 Feb}, pages = {902-13}, abstract = {

Cortical injury may lead to clinical seizures. We investigated the changing patterns of the sleeplike slow oscillation and its tendency to develop into paroxysmal activity consisting of spike-wave (SW) complexes at 2-4 Hz after partial deafferentation of the suprasylvian gyrus. Experiments were carried out in anesthetized cats, at different time intervals (wk 1 to wk 5, W1-W5) after cortical undercut. Multisite field potentials and single or dual intracellular recordings from the whole extent of the deafferented gyrus were used. The field components of the slow oscillation increased in amplitudes and were transformed into paroxysmal patterns, expressed by increased firing rates and tendency to neuronal bursting. The incidence of SW seizures was higher with transition from semiacute (W1) to chronic (W2-W5) stages after cortical undercut. The propagation delay of low-frequency activities decreased from W1 to W5, during both the slow oscillation and seizures. The initiation of seizures took place in territories contiguous to the relatively intact cortex (area 5 in the anterior part of the gyrus), as shown by cross-correlations of field potentials from different sites and simultaneous intracellular recordings from the anterior and posterior parts of the gyrus. The increased amplitudes of both slow oscillation and SW seizures, and their enhanced synchrony expressed by shorter time of propagation, are ascribed to increased neuronal and network excitability after cortical undercut.

}, keywords = {Action Potentials, Afferent Pathways, Animals, Biological Clocks, Cats, Cerebral Cortex, Chronic Disease, Denervation, Electroencephalography, Female, Male, Seizures}, issn = {0022-3077}, doi = {10.1152/jn.00742.2005}, author = {Nita, Dragos A and Ciss{\'e}, Youssouf and Igor Timofeev and Steriade, Mircea} } @article {1593, title = {Slow state transitions of sustained neural oscillations by activity-dependent modulation of intrinsic excitability.}, journal = {J Neurosci}, volume = {26}, year = {2006}, month = {2006 Jun 7}, pages = {6153-62}, abstract = {

Little is known about the dynamics and mechanisms of transitions between tonic firing and bursting in cortical networks. Here, we use a computational model of a neocortical circuit with extracellular potassium dynamics to show that activity-dependent modulation of intrinsic excitability can lead to sustained oscillations with slow transitions between two distinct firing modes: fast run (tonic spiking or fast bursts with few spikes) and slow bursting. These transitions are caused by a bistability with hysteresis in a pyramidal cell model. Balanced excitation and inhibition stabilizes a network of pyramidal cells and inhibitory interneurons in the bistable region and causes sustained periodic alternations between distinct oscillatory states. During spike-wave seizures, neocortical paroxysmal activity exhibits qualitatively similar slow transitions between fast run and bursting. We therefore predict that extracellular potassium dynamics can cause alternating episodes of fast and slow oscillatory states in both normal and epileptic neocortical networks.

}, keywords = {Animals, Cats, Electric Conductivity, Electrophysiology, Extracellular Fluid, Humans, Models, Neurological, Neocortex, Nerve Net, Neurons, Oscillometry, Potassium, Reaction Time, Synapses}, issn = {1529-2401}, doi = {10.1523/JNEUROSCI.5509-05.2006}, author = {Fr{\"o}hlich, Flavio and Bazhenov, Maxim and Igor Timofeev and Steriade, Mircea and Sejnowski, Terrence J} } @article {1599, title = {Synaptic plasticity in local cortical network in vivo and its modulation by the level of neuronal activity.}, journal = {Cereb Cortex}, volume = {16}, year = {2006}, month = {2006 May}, pages = {618-31}, abstract = {




}, keywords = {Action Potentials, Acute Disease, Animals, Brain Injuries, Cats, Chronic Disease, Denervation, Electrodes, Implanted, Epilepsy, Homeostasis, Models, Neurological, Neocortex, Neuronal Plasticity, Periodicity}, issn = {1047-3211}, doi = {10.1093/cercor/bhh184}, author = {Houweling, Arthur R and Bazhenov, Maxim and Igor Timofeev and Steriade, Mircea and Sejnowski, Terrence J} } @article {1605, title = {Membrane bistability in thalamic reticular neurons during spindle oscillations.}, journal = {J Neurophysiol}, volume = {93}, year = {2005}, month = {2005 Jan}, pages = {294-304}, abstract = {


}, keywords = {Action Potentials, Anesthetics, Local, Animals, Biotin, Cats, Computer Simulation, Dose-Response Relationship, Radiation, Electric Stimulation, Electroencephalography, Evoked Potentials, Excitatory Postsynaptic Potentials, Intralaminar Thalamic Nuclei, Lidocaine, Membrane Potentials, Neural Pathways, Neurons, Patch-Clamp Techniques, Periodicity, Synapses, Time Factors}, issn = {0022-3077}, doi = {10.1152/jn.00552.2004}, author = {Fuentealba, Pablo and Igor Timofeev and Bazhenov, Maxim and Sejnowski, Terrence J and Steriade, Mircea} } @article {1609, title = {Contribution of intrinsic neuronal factors in the generation of cortically driven electrographic seizures.}, journal = {J Neurophysiol}, volume = {92}, year = {2004}, month = {2004 Aug}, pages = {1133-43}, abstract = {

Some electrographic seizures are generated intracortically. The cellular and ionic bases of cortically generated spontaneous seizures are not fully understood. Here we investigated spontaneously occurring seizures consisting of spike-wave complexes intermingled with fast runs in ketamine-xylazine anesthetized cats, using dual intracellular recordings in which one pipette contained a control solution and another pipette contained blockers of K(+), Na(+), or Ca(2+) currents. We show that closely located neocortical neurons display virtually identical fluctuations of the membrane potential during electrographic seizures, thus directly demonstrating a high degree of focal synchrony during paroxysmal activity. In addition to synaptic drives, the persistent Na(+) current [I(Na(p))] and probably the high-threshold Ca(2+) current contributed to the generation of paroxysmal depolarizing shifts (PDSs) during cortically driven seizures. Ca(2+)-activated K(+) current [I(K(Ca))] took also part in the control of the amplitude and duration of PDSs. The hyperpolarizing components of seizures largely depended on Cs(+)-sensitive K(+) currents. I(K(Ca)) played a significant, while not exclusive, role in the mediation of hyperpolarizing potentials related to EEG "waves" during spike-wave seizures. We conclude that intrinsic cellular factors have significant role in the generation of depolarizing and hyperpolarizing components of seizures.

}, keywords = {Action Potentials, Anesthetics, Local, Animals, Calcium Channels, Cats, Cerebral Cortex, Cesium, Chelating Agents, Cortical Synchronization, Egtazic Acid, Electroencephalography, Electrophysiology, Lidocaine, Membrane Potentials, Neurons, Potassium Channels, Seizures, Sodium Channels}, issn = {0022-3077}, doi = {10.1152/jn.00523.2003}, author = {Igor Timofeev and Grenier, Fran{\c c}ois and Steriade, Mircea} } @article {1606, title = {Experimental evidence and modeling studies support a synchronizing role for electrical coupling in the cat thalamic reticular neurons in vivo.}, journal = {Eur J Neurosci}, volume = {20}, year = {2004}, month = {2004 Jul}, pages = {111-9}, abstract = {

Thalamic reticular (RE) neurons are crucially implicated in brain rhythms. Here, we report that RE neurons of adult cats, recorded and stained intracellularly in vivo, displayed spontaneously occurring spikelets, which are characteristic of central neurons that are coupled electrotonically via gap junctions. Spikelets occurred spontaneously during spindles, an oscillation in which RE neurons play a leading role, as well as during interspindle lulls. They were significantly different from excitatory postsynaptic potentials and also distinct from fast prepotentials that are presumably dendritic spikes generated synaptically. Spikelets were strongly reduced by halothane, a blocker of gap junctions. Multi-site extracellular recordings performed before, during and after administration of halothane demonstrated a role for electrical coupling in the synchronization of spindling activity within the RE nucleus. Finally, computational models of RE neurons predicted that gap junctions between these neurons could mediate the spread of low-frequency activity at great distances. These experimental and modeling data suggest that electrotonic coupling within the RE nucleus plays an important role in the generation and synchronization of low-frequency (spindling) activities in the thalamus.

}, keywords = {Action Potentials, Anesthetics, Inhalation, Animals, Cats, Excitatory Postsynaptic Potentials, Gap Junctions, Halothane, Models, Animal, Models, Neurological, Neurons, Patch-Clamp Techniques, Synaptic Transmission, Thalamus, Time Factors}, issn = {0953-816X}, doi = {10.1111/j.1460-9568.2004.03462.x}, author = {Fuentealba, Pablo and Crochet, Sylvain and Igor Timofeev and Bazhenov, Maxim and Sejnowski, Terrence J and Steriade, Mircea} } @article {1607, title = {Prolonged hyperpolarizing potentials precede spindle oscillations in the thalamic reticular nucleus.}, journal = {Proc Natl Acad Sci U S A}, volume = {101}, year = {2004}, month = {2004 Jun 29}, pages = {9816-21}, abstract = {

The thalamic reticular (RE) nucleus is a key structure in the generation of spindles, a hallmark bioelectrical oscillation during early stages of sleep. Intracellular recordings of RE neurons in vivo revealed the presence of prolonged hyperpolarizing potentials preceding spindles in a subgroup (30\%) of neurons. These hyperpolarizations (6-10 mV) lasted for 200-300 ms and were present just before the onset of spontaneously occurring spindle waves. Corticothalamic volleys also were effective in generating such hyperpolarizations followed by spindles in RE neurons. A drop of up to 40\% in the apparent input resistance (R(in)) was associated with these hyperpolarizing potentials, suggesting an active process rather than disfacilitation. Accordingly, the reversal potential was approximately -100 mV for both spontaneous and cortically elicited hyperpolarizations, consistent with the activation of slow K(+) conductances. QX-314 in the recording pipettes decreased both the amplitude and incidence of prolonged hyperpolarizations, suggesting the participation of G protein-dependent K(+) currents in the generation of hyperpolarizations. Simultaneous extracellular and intracellular recordings in the RE nucleus demonstrated that some RE neurons discharged during the hyperpolarizations and, thus, may be implicated in their generation. The prolonged hyperpolarizations preceding spindles may play a role in the transition from tonic to bursting firing of RE neurons within a range of membrane potential (-60 to -65 mV) at which they set favorable conditions for the generation of low-threshold spike bursts that initiate spindle sequences. These data are further arguments for the generation of spindles within the thalamic RE nucleus.

}, keywords = {Action Potentials, Aging, Anesthesia, Animals, Cats, Electric Conductivity, Excitatory Postsynaptic Potentials, Ion Transport, Neurons, Potassium, Sleep, Sodium, Thalamic Nuclei}, issn = {0027-8424}, doi = {10.1073/pnas.0402761101}, author = {Fuentealba, Pablo and Igor Timofeev and Steriade, Mircea} } @article {1602, title = {Synaptic enhancement induced through callosal pathways in cat association cortex.}, journal = {J Neurophysiol}, volume = {92}, year = {2004}, month = {2004 Dec}, pages = {3221-32}, abstract = {

The corpus callosum plays a major role in synchronizing neocortical activities in the two hemispheres. We investigated the changes in callosally elicited excitatory postsynaptic potentials (EPSPs) of neurons from cortical association areas 5 and 7 of cats under barbiturate or ketamine-xylazine anesthesia. Single pulses to callosal pathway evoked control EPSPs; pulse-trains were subsequently applied at different frequencies to homotopic sites in the contralateral cortex, as conditioning stimulation; thereafter, the single pulses were applied again to test changes in synaptic responsiveness by comparing the amplitudes of control and conditioned EPSPs. In 41 of 42 neurons recorded under barbiturate anesthesia, all frequencies of conditioning callosal stimuli induced short-term (5-30 min) enhancement of test EPSPs elicited by single stimuli. Neurons tested with successive conditioning pulse-trains at different frequencies displayed stronger enhancement with high-frequency (40-100 Hz) than with low-frequency (10-20 Hz) rhythmic pulse-trains; >100 Hz, the potentiation saturated. In a neuronal sample, microdialysis of an N-methyl-D-aspartate (NMDA) receptor blocker in barbiturate-treated cats suppressed this potentiation, and potentiation of callosally evoked EPSPs was not detected in neurons recorded under ketamine-xylazine anesthesia, thus indicating that EPSPs{\textquoteright} potentiation implicates, at least partially, NMDA receptors. These data suggest that callosal activities occurring within low-frequency and fast-frequency oscillations play a role in cortical synaptic plasticity.

}, keywords = {2-Amino-5-phosphonovalerate, Adrenergic alpha-Agonists, Anesthetics, Intravenous, Animals, Barbiturates, Cats, Corpus Callosum, Electric Stimulation, Excitatory Amino Acid Antagonists, Excitatory Postsynaptic Potentials, Ketamine, Microdialysis, Neocortex, Neural Pathways, Neurons, Receptors, N-Methyl-D-Aspartate, Synapses, Xylazine}, issn = {0022-3077}, doi = {10.1152/jn.00537.2004}, author = {Ciss{\'e}, Youssouf and Crochet, Sylvain and Igor Timofeev and Steriade, Mircea} } @article {1608, title = {Synaptic interactions between thalamic and cortical inputs onto cortical neurons in vivo.}, journal = {J Neurophysiol}, volume = {91}, year = {2004}, month = {2004 May}, pages = {1990-8}, abstract = {

To study the interactions between thalamic and cortical inputs onto neocortical neurons, we used paired-pulse stimulation (PPS) of thalamic and cortical inputs as well as PPS of two cortical or two thalamic inputs that converged, at different time intervals, onto intracellularly recorded cortical and thalamocortical neurons in anesthetized cats. PPS of homosynaptic cortico-cortical pathways produced facilitation, depression, or no significant effects in cortical pathways, whereas cortical responses to thalamocortical inputs were mostly facilitated at both short and long intervals. By contrast, heterosynaptic interactions between either cortical and thalamic, or thalamic and cortical, inputs generally produced decreases in the peak amplitudes and depolarization area of evoked excitatory postsynaptic potentials (EPSPs), with maximal effect at approximately 10 ms and lasting from 60 to 100 ms. All neurons tested with thalamic followed by cortical stimuli showed a decrease in the apparent input resistance (R(in)), the time course of which paralleled that of decreased responses, suggesting that shunting is the factor accounting for EPSP{\textquoteright}s decrease. Only half of neurons tested with cortical followed by thalamic stimuli displayed changes in R(in). Spike shunting in the thalamus may account for those cases in which decreased synaptic responsiveness of cortical neurons was not associated with decreased R(in) because thalamocortical neurons showed decreased firing probability during cortical stimulation. These results suggest a short-lasting but strong shunting between thalamocortical and cortical inputs onto cortical neurons.

}, keywords = {Action Potentials, Animals, Biofeedback, Psychology, Cats, Cerebral Cortex, Electric Stimulation, Electroencephalography, Electrophysiology, Excitatory Postsynaptic Potentials, Kinetics, Neural Pathways, Neurons, Synapses, Thalamus}, issn = {0022-3077}, doi = {10.1152/jn.01105.2003}, author = {Fuentealba, Pablo and Crochet, Sylvain and Igor Timofeev and Steriade, Mircea} } @article {1610, title = {[Cellular basis of transition between sleep and electrographic seizures].}, journal = {Med Sci (Paris)}, volume = {19}, year = {2003}, month = {2003 Oct}, pages = {999-1002}, abstract = {

Epileptic seizures mainly develop during slow-wave sleep. Our experiments, using multi-site, extra- and intracellular recordings, show a transformation without discontinuity from sleep patterns to seizures. The cerebral cortex is the minimal substrate of paroxysms with spike-wave complexes at ~3 Hz. Simultaneously, thalamocortical neurons are steadily inhibited and cannot relay signals from the outside world to cortex. This may explain the unconsciousness during certain types of epilepsy.

}, keywords = {Cerebral Cortex, Electroencephalography, Humans, Seizures, Sleep, Unconsciousness}, issn = {0767-0974}, doi = {10.1051/medsci/20031910999}, author = {Steriade, Mircea and Amzica, Florin and Igor Timofeev} } @article {1613, title = {Electrophysiological properties and input-output organization of callosal neurons in cat association cortex.}, journal = {J Neurophysiol}, volume = {89}, year = {2003}, month = {2003 Mar}, pages = {1402-13}, abstract = {

Intracellular recordings from association cortical areas 5 and 7 were performed in cats under barbiturate or ketamine-xylazine anesthesia to investigate the activities of different classes of neurons involved in callosal pathways, which were electrophysiologically characterized by depolarizing current steps. Excitatory postsynaptic potentials (EPSPs), inhibitory postsynaptic potentials (IPSPs), and/or antidromic responses were elicited by stimulating homotopic sites in the contralateral cortical areas. Differential features of EPSPs related to latencies, amplitudes, and slopes were detected in closely located (50 microm or less) neurons recorded in succession along the same electrode track. In contrast to synchronous thalamocortical volleys that excited most neurons within a cortical column, stimuli applied to homotopic sites in the contralateral cortex activated neurons at restricted cortical depths. Median latencies of callosally evoked EPSPs were 1.5 to 4 ms in various cortical cell-classes. Fast-rhythmic-bursting neurons displayed EPSPs whose amplitudes were threefold larger, and latencies two- or threefold shorter, than those found in the three other cellular classes. Converging callosal and thalamic inputs were recorded in the same cortical neuron. EPSPs or IPSPs were elicited by stimulating foci spaced by <1 mm in the contralateral cortex. In the overwhelming majority of neurons, latencies of antidromic responses were between 1.2 and 3.1 ms; however, some callosal neurons had much longer latencies, }, keywords = {Animals, Cats, Cerebral Cortex, Corpus Callosum, Excitatory Postsynaptic Potentials, Neural Inhibition, Neural Pathways, Neurons, Thalamus}, issn = {0022-3077}, doi = {10.1152/jn.0871.2002}, author = {Ciss{\'e}, Youssouf and Grenier, Fran{\c c}ois and Igor Timofeev and Steriade, Mircea} } @article {1611, title = {Hyperexcitability of intact neurons underlies acute development of trauma-related electrographic seizures in cats in vivo.}, journal = {Eur J Neurosci}, volume = {18}, year = {2003}, month = {2003 Aug}, pages = {486-96}, abstract = {

Cortical trauma can lead to development of electrographic paroxysmal activities. Current views of trauma-induced epileptogenesis suggest that chronic neuronal hyperexcitability and extensive morphological reorganization of the traumatized cortex are required for the generation of electrographic seizures. However, the mechanisms responsible for the initiation of electrographic seizures shortly after cortical injury are poorly understood. Here we show that, in the experimental model of partially deafferented (undercut) cortex, an increase in intrinsic and synaptic excitability of neurons in areas adjacent to the undercut cortex is sufficient for the generation of electrographic paroxysmal activity within few hours after partial cortical deafferentation. Locally increased and spatially restricted neuronal excitability arose from the increased incidence of intrinsically bursting neurons, enhanced intrinsic and synaptic neuronal responsiveness, and slight disinhibition. These mechanisms only operate in neurons located in the vicinity of partially deafferented sites because, after the cortical injury, partially deafferented neurons are mostly silent and hypoexcitable. Our results suggest that trauma-induced electrographic seizures first arise in cortical fields that are closest to the site of injury and such seizures do not require long-term neuronal reorganization.

}, keywords = {Animals, Brain Injuries, Cats, Cerebral Cortex, Denervation, Electroencephalography, Electrophysiology, Epilepsy, Female, Male, Neural Inhibition, Neurons, Synapses}, issn = {0953-816X}, author = {Topolnik, Lisa and Steriade, Mircea and Igor Timofeev} } @article {1615, title = {Neocortical very fast oscillations (ripples, 80-200 Hz) during seizures: intracellular correlates.}, journal = {J Neurophysiol}, volume = {89}, year = {2003}, month = {2003 Feb}, pages = {841-52}, abstract = {

Multi-site field potential and intracellular recordings from various neocortical areas were used to study very fast oscillations or ripples (80-200 Hz) during electrographic seizures in cats under ketamine-xylazine anesthesia. The animals displayed spontaneously occurring and electrically induced seizures comprising spike-wave complexes (2-3 Hz) and fast runs (10-20 Hz). Neocortical ripples had much higher amplitudes during seizures than during the slow oscillation preceding the onset of seizures. A series of experimental data from the present study supports the hypothesis that ripples are implicated in seizure initiation. Ripples were particularly strong at the onset of seizures and halothane, which antagonizes the occurrence of ripples, also blocked seizures. The firing of electrophysiologically defined cellular types was phase-locked with ripples in simultaneously recorded field potentials. This indicates that ripples during paroxysmal events are associated with a coordination of firing in a majority of neocortical neurons. This was confirmed with dual intracellular recordings. Based on the amplitude that neocortical ripples reach during paroxysmal events, we propose a mechanism by which neocortical ripples during normal network activity could actively participate in the initiation of seizures on reaching a certain threshold amplitude. This mechanism involves a vicious feedback loop in which very fast oscillations in field potentials are a reflection of synchronous action potentials, and in turn these oscillations help generate and synchronize action potentials in adjacent neurons through electrical interactions.

}, keywords = {Animals, Cats, Chlorides, Electric Stimulation, Electrodes, Electroencephalography, Epilepsy, Membrane Potentials, Neocortex, Neural Pathways, Neuroglia, Neurons, Periodicity}, issn = {0022-3077}, doi = {10.1152/jn.00420.2002}, author = {Grenier, Fran{\c c}ois and Igor Timofeev and Steriade, Mircea} } @article {1614, title = {Neuronal plasticity in thalamocortical networks during sleep and waking oscillations.}, journal = {Neuron}, volume = {37}, year = {2003}, month = {2003 Feb 20}, pages = {563-76}, abstract = {


}, keywords = {Animals, Biological Clocks, Cats, Cerebral Cortex, Electroencephalography, Humans, Nerve Net, Neuronal Plasticity, Neurons, Rats, Sleep, Thalamus, Wakefulness}, issn = {0896-6273}, author = {Steriade, Mircea and Igor Timofeev} } @article {1612, title = {Partial cortical deafferentation promotes development of paroxysmal activity.}, journal = {Cereb Cortex}, volume = {13}, year = {2003}, month = {2003 Aug}, pages = {883-93}, abstract = {

This study tested the hypothesis that early functional alterations in neuronal synchrony in the partially deafferented cortex may lead to spontaneously occurring electrographic seizures. In vivo experiments with partial deafferentation of cat suprasylvian gyrus after extensive undercut of the white matter were conducted using multi-site EEG, extracellular unit and intracellular recordings. The amplitudes of EEG waves were much higher in the areas surrounding deafferented cortical fields as compared with control and with undercut cortex. In 40\% of animals with undercut cortex, paroxysmal activity occurred 2-3 h after the undercut and was initiated in the relatively intact cortex, adjacent to the more disconnected one. The seizures that followed the undercut consisted of spike-wave/polyspike-wave complexes and fast runs, resembling the electrographic patterns of some clinical epileptic syndromes. An increased local synchrony in the relatively intact cortex evolved into paroxysmal activity that ultimately spread to the deafferented cortex. The electrographic seizures were found only in animals that showed a propagation of the slow sleep-like oscillation in control conditions. The increase of long-range synchrony within a given seizure was associated with seizure termination. These results indicate that alterations in neuronal synchrony following neuronal trauma can be a critical factor triggering electrographic seizures.

}, keywords = {Animals, Cats, Cerebral Cortex, Electroencephalography, Female, Male, Narcolepsy, Seizures}, issn = {1047-3211}, author = {Topolnik, Lisa and Steriade, Mircea and Igor Timofeev} } @article {1619, title = {Cortical hyperpolarization-activated depolarizing current takes part in the generation of focal paroxysmal activities.}, journal = {Proc Natl Acad Sci U S A}, volume = {99}, year = {2002}, month = {2002 Jul 9}, pages = {9533-7}, abstract = {

During paroxysmal neocortical oscillations, sudden depolarization leading to the next cycle occurs when the majority of cortical neurons are hyperpolarized. Both the Ca(2+)-dependent K(+) currents (I(K(Ca))) and disfacilitation play critical roles in the generation of hyperpolarizing potentials. In vivo experiments and computational models are used here to investigate whether the hyperpolarization-activated depolarizing current (I(h)) in cortical neurons also contributes to the generation of paroxysmal onsets. Hyperpolarizing current pulses revealed a depolarizing sag in approximately 20\% of cortical neurons. Intracellular recordings from glial cells indirectly indicated an increase in extracellular potassium concentration ([K(+)](o)) during paroxysmal activities, leading to a positive shift in the reversal potential of K(+)-mediated currents, including I(h). In the paroxysmal neocortex, approximately 20\% of neurons show repolarizing potentials originating from hyperpolarizations associated with depth-electroencephalogram positive waves of spike-wave complexes. The onset of these repolarizing potentials corresponds to maximal [K(+)](o) as estimated from dual simultaneous impalements from neurons and glial cells. Computational models showed how, after the increased [K(+)](o), the interplay between I(h), I(K(Ca)), and a persistent Na(+) current, I(Na(P)), could organize paroxysmal oscillations at a frequency of 2-3 Hz.

}, keywords = {Animals, Bicuculline, Cats, Convulsants, Electroencephalography, Electrophysiology, Evoked Potentials, Neocortex, Neuroglia, Neurons, Potassium, Seizures, Sodium}, issn = {0027-8424}, doi = {10.1073/pnas.132259899}, author = {Igor Timofeev and Bazhenov, Maxim and Sejnowski, Terrence and Steriade, Mircea} } @article {1617, title = {Frequency-selective augmenting responses by short-term synaptic depression in cat neocortex.}, journal = {J Physiol}, volume = {542}, year = {2002}, month = {2002 Jul 15}, pages = {599-617}, abstract = {


}, keywords = {Animals, Brain, Cats, Cortical Spreading Depression, Electric Stimulation, In Vitro Techniques, Interneurons, Models, Neurological, Neocortex, Nerve Net, Neuronal Plasticity, Pyramidal Cells, Synapses, Thalamus, Time Factors}, issn = {0022-3751}, author = {Houweling, Arthur R and Bazhenov, Maxim and Igor Timofeev and Grenier, Fran{\c c}ois and Steriade, Mircea and Sejnowski, Terrence J} } @article {1616, title = {Model of thalamocortical slow-wave sleep oscillations and transitions to activated States.}, journal = {J Neurosci}, volume = {22}, year = {2002}, month = {2002 Oct 1}, pages = {8691-704}, abstract = {


}, keywords = {Action Potentials, Animals, Biological Clocks, Calcium, Cats, Computer Simulation, Electroencephalography, Excitatory Postsynaptic Potentials, Models, Neurological, Neocortex, Neural Networks (Computer), Neurons, Poisson Distribution, Potassium, Sleep, Sleep, REM, Sodium, Thalamus, Wakefulness}, issn = {1529-2401}, author = {Bazhenov, Maxim and Igor Timofeev and Steriade, Mircea and Sejnowski, Terrence J} } @article {1618, title = {Short- and medium-term plasticity associated with augmenting responses in cortical slabs and spindles in intact cortex of cats in vivo.}, journal = {J Physiol}, volume = {542}, year = {2002}, month = {2002 Jul 15}, pages = {583-98}, abstract = {

