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PubMed2006

Spatial representation of neural responses to natural and altered conspecific vocalizations in cat auditory cortex.

This study shows the neural representation of cat vocalizations, natural and altered with respect to carrier and envelope, as well as time-reversed, in four different areas of the auditory cortex. Multiunit activity recorded in primary auditory cortex (AI) of anesthetized cats mainly occurred at onsets (<200-ms latency) and at subsequent major peaks of the vocalization envelope and was significantly inhibited during the stationary course of the stimuli. The first 200 ms of processing appears crucial for discrimination of a vocalization in AI. The dorsal and ventral parts of AI appear to have different roles in coding vocalizations. The dorsal part potentially discriminated carrier-altered meows, whereas the ventral part showed differences primarily in its response to natural and time-reversed meows. In the posterior auditory field, the different temporal response types of neurons, as determined by their poststimulus time histograms, showed discrimination for carrier alterations in the meow. Sustained firing neurons in the posterior ectosylvian gyrus (EP) could discriminate, among others, by neural synchrony, temporal envelope alterations of the meow, and time reversion thereof. These findings suggest an important role of EP in the detection of information conveyed by the alterations of vocalizations. Discrimination of the neural responses to different alterations of vocalizations could be based on either firing rate, type of temporal response, or neural synchrony, suggesting that all these are likely simultaneously used in processing of natural and altered conspecific vocalizations.

Acoustic Stimulation↗
PubMed2004

Statistical method for detection of phase-locking episodes in neural oscillations.

In many networks of oscillatory neurons, synaptic interactions can promote the entrainment of units into phase-coupled groups. The detection of synchrony in experimental data, especially if the data consist of single-trial runs, can be problematic when, for example, phase entrainment is of short duration, buried in noise, or masked by amplitude fluctuations that are uncorrelated among the oscillating units. In the present study, we tackle the problem of detecting neural interactions from pairs of oscillatory signals in a narrow frequency band. To avoid the interference of amplitude fluctuations in the detection of synchrony, we extract a phase variable from the data and utilize statistical indices to measure phase locking. We use three different phase-locking indices based on coherence, entropy, and mutual information between the phase variables. Phase-locking indices are calculated over time using sliding analysis windows. By varying the duration of the analysis windows, we were able to inspect the data at different levels of temporal resolution and statistical reliability. The statistical significance of high index values was evaluated using four different surrogate data methods. We determined phase-locking indices using alternative methods for generating surrogate data and found that results are sensitive to the particular method selected. Surrogate methods that preserve the temporal structure of the individual phase time series decrease substantially the number of false positives when tested on a pair of independent signals.

Acoustic Stimulation↗
PubMed2003

Temperature-induced reciprocal activation of hippocampal field activity.

Hippocampal network activity oscillates between sustained rhythms (e.g., theta) and aperiodic population spikes (e.g., sharp waves, dentate spikes). Although temperature is known to modulate various aspects of rhythmic hippocampal activity, little is known regarding the influence of temperature on the incidence of population spikes. We recorded spontaneous hippocampal activity along the CA1-dentate gyrus axis using multisite silicon electrodes in urethanized infant rats (P2-P16) at brain temperatures of 37 and 27 degrees C. Theta and gamma activity, as well as sharp waves, were detected at 37 degrees C but not at 27 degrees C. In contrast, dentate spikes were rare at 37 degrees C but their incidence increased several-fold at 27 degrees C (epileptiform activity also emerged at 27 degrees C in the oldest pups). This surprising increase in the incidence of dentate spike activity in a cold brain represents the first such demonstration for a neuronal field pattern. In addition, these findings indicate that changes in brain temperature produce systems-level shifts in the balance among reciprocally interacting hippocampal components.

Age Factors↗
PubMed2005

Activation of nucleus basalis facilitates cortical control of a brain stem motor program.

We tested the hypothesis that activation of nucleus basalis magnocellularis (NBM), which provides cholinergic input to cortex, facilitates motor control. Our measures of facilitation were changes in the direction and time-course of vibrissa movements that are elicited by microstimulation of vibrissa motor (M1) cortex. In particular, microstimulation led solely to a transient retraction of the vibrissae in the sessile animal but to a full motion sequence of protraction followed by retraction in the aroused animal. We observed that activation of NBM, as assayed by cortical desynchronization, induced a transition from microstimulation-evoked retraction to full sweep sequences. This dramatic change in the vibrissa response to microstimulation was blocked by systemic delivery of atropine and, in anesthetized animals, an analogous change was blocked by the topical administration of atropine to M1 cortex. We conclude that NBM significantly facilitates the ability of M1 cortex to control movements. Our results bear on the importance of cholinergic activation in schemes for neuroprosthetic control of movement.

Animals↗
PubMed1984

Visual desynchronization of cortical EEG impaired by lesions of superior colliculus in rats.

It is unclear whether rats with lesions of the superior colliculus (SC) neglect visual stimuli because a) they fail to notice the stimuli or b) they notice the stimuli but fail to make specific orienting movements of the eyes and head toward them. To investigate this issue, we used an index of "noticing" that does not involve overt orienting movements, namely, desynchronization of the cortical electroencephalogram (EEG) in drowsy animals. In the first experiment, large collicular lesions with some invasion of surrounding areas severely impaired EEG desynchronization to a brief overhead flash of light but did not significantly affect desynchronization to brief bursts of white noise. No impairment was found after control lesions of cerebral cortex overlying the superior colliculus or of striate cortex. A subsequent experiment found that the visual impairment was still present when lesions were confined to the superior colliculus. It appears that rats with lesions of the superior colliculus can, in certain circumstances, fail to notice visual stimuli and that in rats, the superior colliculus is concerned not only with specific orienting movements to visual stimuli but also with visual desynchronization of the cortical EEG.

Animals↗
PubMed1997

Modulatory effects of regional cortical activation on the onset responses of the cat medial geniculate neurons.

Corticofugal modulation on activity of the medial geniculate body (MGB) was examined by locally activating the primary auditory cortex (AI) and looking for effects on the onset responses of MGB neurons to acoustic stimuli. Of 103 MGB neurons recorded from 13 hemispheres of 11 animals, 91 neurons (88%) showed either a facilitatory or inhibitory effect or both; of these neurons, 72 showed facilitatory effects and 25 inhibitory effects. The average facilitatory effect was large, with a mean increase of 62.4%. Small inhibitory effects (mean: -16.2%) were obtained from a few neurons (6 of 103) when a pure tone stimulus was used, whereas the effect became larger and more frequent when a noise burst stimulus was used (mean: -27.3%, n = 22 of 27 neurons). Activation of an AI site having the same best frequency (BF) as the MGB neuron being recorded from produced mainly a facilitatory effect on MGB neuronal responses to pure tones. Activation of AI at a site neighboring the BF site produced inhibitory effects on the MGB response when noise burst stimuli were used. We found that the effective stimulation sites in AI that could modulate MGB activity formed patchlike maps with a diameter of 1.13 +/- 0.09 (SE) mm (range 0.6-1.9 mm, n = 15) being larger than the patches of thalamocortical terminal fields. Examining the effects of sound intensities, of 18 neurons tested 9 neurons showed a larger effect for low-sound-intensity stimuli and small or no effects for high-sound-intensity stimuli. These were named low-sound-intensity effective neurons. Five neurons showed high sound intensity effectiveness and four were non-intensity specific. Most low-sound-intensity effective neurons were monotonic rate-intensity function neurons. The AI cortical modulatory effect was frequency specific, because 15 of 27 neurons showed a larger facilitatory effect when a BF stimulus was used rather than a stimulus of any other frequency. The corticothalamic connection between the recording site in MGB and the most effective stimulation site in AI was confirmed by injecting wheat germ agglutinin-horseradish peroxidase tracer at the stimulation site and producing a small lesion in the recording site. The results suggest that 1) the large facilitation effects obtained by AI activation at the region that directly projected to the MGB could be the result mainly of the direct projection terminals to the MGB relay neurons; 2) the large size patches of the effective stimulation site in AI could be due to widely ramifying corticothalamic projections; and 3) the corticofugal projection selectively gates auditory information mainly by a facilitatory effect, although there is also an inhibitory effect that depends on the sound stimulus used.

Acoustic Stimulation↗
PubMed1997

Dynamic interactions determine partial thalamic quiescence in a computer network model of spike-and-wave seizures.

In vivo intracellular recording from cat thalamus and cortex was performed during spontaneous spike-wave seizures characterized by synchronously firing cortical neurons correlated with the electroencephalogram. During these seizures, thalamic reticular (RE) neurons discharged with long spike bursts riding on a depolarization, whereas thalamocortical (TC) neurons were either entrained into the seizures (40%) or were quiescent (60%). During quiescence, TC neurons showed phasic inhibitory postsynaptic potentials (IPSPs) that coincided with paroxysmal depolarizing shifts in the simultaneously recorded cortical neuron. Computer simulations of a reciprocally connected TC-RE pair showed two major modes of TC-RE interaction. In one mode, a mutual oscillation involved direct TC neuron excitation of the RE neuron leading to a burst that fed back an IPSP into the TC neuron, producing a low-threshold spike. In the other, quiescent mode, the TC neuron was subject to stronger coalescing IPSPs. Simulated cortical stimulation could trigger a transition between the two modes. This transition could go in either direction and was dependent on the precise timing of the input. The transition did not always follow the stimulation immediately. A larger, multicolumnar simulation was set up to assess the role of the TC-RE pair in the context of extensive divergence and convergence. The amount of TC neuron spiking generally correlated with the strength of total inhibitory input, but large variations in the amount of spiking could be seen. Evidence for mutual oscillation could be demonstrated by comparing TC neuron firing with that in reciprocally connected RE neurons. An additional mechanism for TC neuron quiescence was assessed with the use of a cooperative model of gamma-aminobutyric acid-B (GABA(B))-mediated responses. With this model, RE neurons receiving repeated strong excitatory input produced TC neuron quiescence due to burst-duration-associated augmentation of GABA(B) current. We predict the existence of spatial inhomogeneity in apparently generalized spike-wave seizures, involving a center-surround pattern. In the center, intense cortical and RE neuron activity would be associated with TC neuron quiescence. In the surround, less intense hyperpolarization of TC neurons would allow low-threshold spikes to occur. This surround, an "epileptic penumbra," would be the forefront of the expanding epileptic wave during the process of initial seizure generalization. Therapeutically, we would then predict that agents that reduce TC neuron activity would have a greater effect on seizure onset than on ongoing spike-wave seizures or other thalamic oscillations.

Action Potentials↗
PubMed1997

Physiology, pharmacology, and topography of cholinergic neocortical oscillations in vitro.

Rat neocortical brain slices generated rhythmic extracellular field [microelectroencephalogram (micro-EEG)] oscillations at theta frequencies (3-12 Hz) when exposed to pharmacological conditions that mimicked endogenous ascending cholinergic and GABAergic inputs. Use of the specific receptor agonist and antagonist carbachol and bicuculline revealed that simultaneous muscarinic receptor activation and gamma-aminobutyric acid-A (GABA(A))-mediated disinhibition were necessary to elicit neocortical oscillations. Rhythmic activity was independent of GABA(B) receptor activation, but required intact glutamatergic transmission, evidenced by blockade or disruption of oscillations by 6-cyano-7-nitroquinoxaline-2,3-dione and (+/-)-2-amino-5-phosphonovaleric acid, respectively. Multisite mapping studies showed that oscillations were localized to areas 29d and 18b (Oc2MM) and parts of areas 18a and 17. Peak oscillation amplitudes occurred in layer 2/3, and phase reversals were observed in layers 1 and 5. Current source density analysis revealed large-amplitude current sinks and sources in layers 2/3 and 5, respectively. An initial shift in peak inward current density from layer 1 to layer 2/3 indicated that two processes underlie an initial depolarization followed by oscillatory activity. Laminar transections localized oscillation-generating circuitry to superficial cortical layers and sharp-spike-generating circuitry to deep cortical layers. Whole cell recordings identified three distinct cell types based on response properties during rhythmic micro-EEG activity: oscillation-ON (theta-ON) and -OFF (theta-OFF) neurons, and transiently depolarizing glial cells. Theta-ON neurons displayed membrane potential oscillations that increased in amplitude with hyperpolarization (from -30 to -90 mV). This, taken together with a glutamate antagonist-induced depression of rhythmic micro-EEG activity, indicated that cholinergically driven neocortical oscillations require excitatory synaptic transmission. We conclude that under the appropriate pharmacological conditions, neocortical brain slices were capable of producing localized theta frequency oscillations. Experiments examining oscillation physiology, pharmacology, and topography demonstrated that neocortical brain slice oscillations share many similarities with the in vivo and in vitro theta EEG activity recorded in other brain regions.

Animals↗
PubMed1998

Spike-wave complexes and fast components of cortically generated seizures. II. Extra- and intracellular patterns.

In the previous paper we have demonstrated, by means of field potential and extracellular unit recordings, that bicuculline-induced seizures, which include spike-wave (SW) or polyspike-wave (PSW) complexes, are initiated intracortically and survive ipsilateral thalamectomy. Here, we used multisite field potential and extracellular recordings to validate the patterns of cortical SW/PSW seizures in chronically implanted, behaving cats. To investigate the cellular patterns and excitability during spontaneously occurring and electrically elicited cortical seizures, we used single and dual intracellular recordings from regular-spiking (RS) and fast-rhythmic-bursting (FRB) cortical neurons, in conjunction with field potential recordings from neocortex and related thalamic nuclei, in cats maintained under ketamine-xylazine anesthesia. 1) Invariably, the spontaneous or electrically induced seizures were initiated within the cortex of both behaving and anesthetized animals. Spontaneously occurring, compound seizures consisting of SW/PSW complexes at 2-4 Hz and fast runs at 10-15 Hz, developed without discontinuity from the slow (mainly 0.5-0.9 Hz), sleeplike, cortically generated oscillation. 2) During SW/PSW complexes, RS neurons discharged spike trains during the depth-negative component of the cortical "spike" component of field potentials and were hyperpolarized during the depth-positive field wave. The FRB neurons fired many more action potentials than RS cells during SW/PSW complexes. Averaged activities triggered by the spiky field potentials or by the steepest slope of depolarization in cortical neurons demonstrated similar relations between intracellular activities and field potentials during sleep and seizure epochs, the latter-being an exaggeration of the depolarizing and hyperpolarizing components of the slow sleep oscillation. 3) During the fast runs, RS cells were tonically depolarized and discharged single action potentials or spike doublets (usually with pronounced spike inactivation), whereas FRB cells discharged rhythmic spike bursts, time locked with the depth-negative field potentials. 4) Neuronal excitability, tested by depolarizing current pulses applied throughout the seizures and compared with pre- and postseizure epochs, showed a decreased number of evoked action potentials during both seizure components (SW/PSW complexes and fast runs), eventually leading to null responses during the postictal depression. 5) Data suggest that interconnected FRB neurons may play an important role in the initiation of cortical seizures. We discuss the similarities between the electrographic patterns described in this study and those found in different forms of clinical seizures.

Anesthesia↗
PubMed2006

Spatially filtered magnetoencephalographic analysis of cortical oscillatory changes in basic brain rhythms during the Japanese 'Shiritori' Word Generation Task.

BACKGROUND: 'Shiritori' (capping verses) is a traditional Japanese word generation game, and is very familiar to native Japanese speakers. The shiritori task is expected to more strongly activate temporal language-related regions than conventional word generation to letters because of its characteristic way to make cue letters. OBJECTIVES: The aim of this study was to examine the cortical oscillatory changes in basic brain rhythms during silently performing a shiritori task. METHODS: Using synthetic aperture magnetometry (SAM) analysis of magnetoencephalography, we estimated the tomographic distributions of the statistically significant differences of the power in the alpha and beta frequency bands between the resting and the task periods. RESULTS: Significant event-related desynchronization (ERD) in the 8- to 25-Hz band, thought to reflect neural activation, was localized within task-related cortical regions with left-side dominance. The significant ERDs were estimated in both the frontal and temporal language-related regions encompassing Broca's and Wernicke's areas, although previous neuroimaging studies using word generation to letters showed neural activation predominantly in frontal regions. CONCLUSIONS: Our results show the potential of SAM analysis for reliable brain mapping of language processing, and suggest that the shiritori task might be more suitable for examining the language-related network in the brain than conventional word generation to letters.

Adult↗
PubMed1994

Dexamethasone and hormones related to the hypothalamic-pituitary-adrenal axis modulate inherited neocortical spindling in DBA/2J mice.

The role of dexamethasone and hormones related to the hypothalamic-pituitary-adrenal (HPA) axis (corticotropin-releasing factor, adrenocorticotropic hormone, corticosterone) in the control of the spike-and-wave spindling episodes (S&W) which can be spontaneously recorded in the electrocorticogram (ECoG) of DBA/2J mice was investigated. Both dexamethasone and hormones related to the HPA axis consistently reduced the S&W in DBA/2J mice. Cycloheximide (a protein synthesis inhibitor) pretreatment significantly delayed the reducing effect of dexamethasone on the S&W in mice. After a transitory decrease, the glucocorticoid receptor antagonist RU-38486 induced a dramatic increase in the rate of the S&W episodes. In addition, mice treated with RU-38486 for 4 days showed a significant increase in the S&W 24 h after the 4th treatment. Our results indicate that dexamethasone as well as hormones related to the HPA axis are able to modulate the S&W in DBA/2J mice, suggesting that this effect may be bound to corticosteroid activity. The time lag (30-60 min) which is necessary for revealing the reducing influence of dexamethasone on the S&W in mice and the influence exerted by cycloheximide on dexamethasone activity support the hypothesis that the effect induced by dexamethasone may be at least in part dependent on genomic mechanisms.

Adrenocorticotropic Hormone↗
PubMed1995

Clinical case report: opiate antagonist and event-related desynchronization in 2 autistic boys.

Event-related desynchronization and visual orientational behavior were examined in 2 autistic boys to determine if blockade of endogenous opioid activity facilitates cognitive processing at a cortical level. Before naltrexone, the boys showed no selective alpha blocking during exposure to either mother's pictures or white light. Unlike normals, they exhibited strong alpha band enhancement at temporocentral recording sites. Two hours after administering 0.5 mg/kg naltrexone, mother-as well as light-related alpha blocking appeared at occipital, occipitotemporal, and prefrontal sites. These effects were gone 24 h after dosing in one child, but persisted in the other. A parallel increase in visual pursuit in a social context was observed. These results affirm that autistic gaze aversion can be caused by excessive opioid activity interfering with corticothalamocortical processing of visual stimuli.

Alpha Rhythm↗
PubMed1981

Effect of opiates on the caudate spindle in the cat.

The effect of opiate drugs on the caudate spindle (CS) in the cat was observed following both systemic and intracaudal administration. Systemic administration of morphine, pentazocine and pethidine inhibited the CS. The inhibitory effects of opiates were antagonized by lysergide and methysergide but not by naloxone, chlorpromazine, dehydrobenzperidol, amphetamine and atropine. Contrary to their systemic administration, the investigated opiates morphine, pentazocine, pethidine and Met5-Enkephaline enhanced the CS, when injected into the caudate nucleus close to the site of stimulation. Those facilitating effects of opiates on the CS were completely blocked by naloxone. The results suggest that serotoninergic mechanisms might be involved in the action of opiates on the neuronal activity of the caudate nucleus.

Animals↗
PubMed2005

Rate and synchrony in feedforward networks of coincidence detectors: analytical solution.

We provide an analytical recurrent solution for the firing rates and cross-correlations of feedforward networks with arbitrary connectivity, excitatory or inhibitory, in response to steady-state spiking input to all neurons in the first network layer. Connections can go between any two layers as long as no loops are produced. Mean firing rates and pairwise cross-correlations of all input neurons can be chosen individually. We apply this method to study the propagation of rate and synchrony information through sample networks to address the current debate regarding the efficacy of rate codes versus temporal codes. Our results from applying the network solution to several examples support the following conclusions: (1) differential propagation efficacy of rate and synchrony to higher layers of a feedforward network is dependent on both network and input parameters, and (2) previous modeling and simulation studies exclusively supporting either rate or temporal coding must be reconsidered within the limited range of network and input parameters used. Our exact, analytical solution for feedforward networks of coincidence detectors should prove useful for further elucidating the efficacy and differential roles of rate and temporal codes in terms of different network and input parameter ranges.

Action Potentials↗
PubMed2006

Visual grouping and the focusing of attention induce gamma-band oscillations at different frequencies in human magnetoencephalogram signals.

Neural oscillatory synchrony could implement grouping processes, act as an attentional filter, or foster the storage of information in short-term memory. Do these findings indicate that oscillatory synchrony is an unspecific epiphenomenon occurring in any demanding task, or that oscillatory synchrony is a fundamental mechanism involved whenever neural cooperation is requested? If the latter hypothesis is true, then oscillatory synchrony should be specific, with distinct visual processes eliciting different types of oscillations. We recorded magnetoencephalogram (MEG) signals while manipulating the grouping properties of a visual display on the one hand, and the focusing of attention to memorize part of this display on the other hand. Grouping-related gamma oscillations were present in all conditions but modulated by the grouping properties of the stimulus (one or two groups) in the high gamma-band (70-120 Hz) at central occipital locations. Attention-related gamma oscillations appeared as an additional component whenever attentional focusing was requested in the low gamma-band (44-66 Hz) at parietal locations. Our results thus reveal the existence of a functional specialization in the gamma range, with grouping-related oscillations showing up at higher frequencies than attention-related oscillations. The pattern of oscillatory synchrony is thus specific of the visual process it is associated with. Our results further suggest that both grouping processes and focused attention rely on a common implementation process, namely, gamma-band oscillatory synchrony, a finding that could account for the fact that coherent percepts are more likely to catch attention than incoherent ones.

Adult↗
PubMed2007

Distinction between perceptual and attentional processing in working memory tasks: a study of phase-locked and induced oscillatory brain dynamics.

Working memory involves the short-term storage and manipulation of information necessary for cognitive performance, including comprehension, learning, reasoning and planning. Although electroencephalogram (EEG) rhythms are modulated during working memory, the temporal relationship of EEG oscillations with the eliciting event has not been well studied. In particular, the dynamics of the neural network supporting memory processes may be best captured in induced oscillations, characterized by a loose temporal link with the stimulus. In order to differentiate induced from evoked functional processes, the present study proposes a time-frequency analysis of the 3 to 30 Hz EEG oscillatory activity in a verbal n-back working memory paradigm. Control tasks were designed to identify oscillatory activity related to stimulus presentation (passive task) and focused attention to the stimulus (detection task). Evoked theta activity (4-8 Hz) phase-locked to the visual stimulus was evidenced in the parieto-occipital region for all tasks. In parallel, induced theta activity was recorded in the frontal region for detection and n-back memory tasks, but not for the passive task, suggesting its dependency on focused attention to the stimulus. Sustained induced oscillatory activity was identified in relation to working memory in the theta and beta (15-25 Hz) frequency bands, larger for the highest memory load. Its late occurrence limited to nonmatched items suggests that it could be related to item retention and active maintenance for further task requirements. Induced theta and beta activities displayed respectively a frontal and parietal topographical distribution, providing further functional information on the fronto-posterior network supporting working memory.

Adult↗