Synchronization of local neural networks in the somatosensory cortex: A comparison of stationary and moving stimuli.
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Spontaneous and stimulus-induced responses were recorded from neighboring groups of neurons by an array of electrodes in the primary (SI) somatosensory cortex of intact, halothane-anesthetized cats. Cross-correlation analysis was used to characterize the coordination of spontaneous activity and the responses to peripheral stimulation with moving or stationary air jets. Although synchronization was detected in only 10% (88 of 880) of the pairs of single neurons that were recorded, cross-correlation analysis of multiunit responses revealed significant levels of synchronization in 64% of the 123 recorded electrode pairs. Compared with spontaneous activity, both stationary and moving air jets caused substantial increases in the rate, proportion, and temporal precision of synchronized activity in local regions of SI cortex. Among populations of neurons that were synchronized by both types of air-jet stimulation, the mean rate of synchronized activity was significantly higher during moving air-jet stimulation than during stationary air-jet stimulation. Moving air jets also produced significantly higher correlation coefficients than stationary air jets in the raw cross-correlograms (CCGs) but not in the shift-corrected CCGs. The incidence and rate of stimulus-induced synchronization varied with the distance separating the recording sites. For sites separated by /=500 microm, only 37% of the multiunit responses were synchronized by discrete stimulation with a single air jet. Measurements of the multiunit CCG peak half-widths showed that the correlated activity produced by moving air jets had slightly less temporal variability than that produced by stationary air jets. These results indicate that moving stimuli produce greater levels of synchronization than stationary stimuli among local groups of SI neurons and suggest that neuronal synchronization may supplement the changes in firing rate which code intensity and other attributes of a cutaneous stimulus. (+info)
Cross-correlation study of the temporal interactions between areas V1 and V2 of the macaque monkey.
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Cross-correlation studies performed in cat visual cortex have shown that neurons in different cortical areas of the same hemisphere or in corresponding areas of opposite hemispheres tend to synchronize their activities. The presence of synchronization may be related to the parallel organization of the cat visual system, in which different cortical areas can be activated in parallel from the lateral geniculate nucleus. We wanted to determine whether interareal synchronization of firing can also be observed in the monkey, in which cortical areas are thought to be organized in a hierarchy spanning different levels. Cross-correlation histograms (CCHs) were calculated from pairs of single or pairs of multiunit activities simultaneously recorded in areas V1 and V2 of paralyzed and anesthetized macaque monkeys. Moving bars and flashed bars were used as stimuli. The shift predictor was calculated and subtracted from the raw CCH to reveal interactions of neuronal origin in isolation. Significant CCH peaks, indicating interactions of neuronal origin, were obtained in 11% of the dual single-unit recordings and 46% of the dual multiunit recordings with moving bars. The incidence of nonflat CCHs with flashed bars was 29 and 78%, respectively. For the pairs of recording sites where both flashed and moving stimuli were used, the incidences of significant CCHs were very similar. Three types of peaks were distinguished on the basis of their width at half-height: T (<16 ms), C (between 16 and 180 ms), and H peaks (>180 ms). T peaks were very rarely observed (<1% in single-unit recordings). H peaks were observed in 7-16% of the single-unit CCHs, and C peaks in 6-16%, depending on the stimulus used. C and H peaks were observed more often when the receptive fields were overlapping or distant by <2 degrees. To test for the presence of synchronization between neurons in areas V1 and V2, we measured the position of the CCH peak with respect to the origin of the time axis of the CCH. Only in the case of a few T peaks did we find displaced peaks, indicating a possible drive of the V2 neuron by the simultaneously recorded V1 cell. All the other peaks were either centered on the origin or overlapped the origin of time with their upper halves. Thus similarly to what has been reported for the cat, neurons belonging to different cortical areas in the monkey tend to synchronize the time of emission of their action potentials with three different levels of temporal precision. For peaks calculated from flashed stimuli, we compared the peak position with the difference between latencies of V1 and V2 neurons. There was a clear correlation for single-unit pairs in the case of C peaks. Thus the position of a C peak on the time axis appears to reflect the order of visual activation of the correlated neurons. The coupling strength for H peaks was smaller during visual drive compared with spontaneous activity. On the contrary, C peaks were seen more often and were stronger during visual stimulation than during spontaneous activity. This suggests that C-type synchronization is associated with the processing of visual information. The origin of synchronized activity in a serially organized system is discussed. (+info)
Coherent oscillations in membrane potential synchronize impulse bursts in central olfactory neurons of the crayfish.
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Lateral protocerebral interneurons (LPIs) in the central olfactory pathway of the freshwater crayfish Procambarus clarkii reside within the lateral protocerebrum and receive direct input from projection neurons of the olfactory midbrain. The LPIs exhibit periodic (0.5 Hz) changes in membrane potential that are imposed on them synaptically. Acute surgical experiments indicate that the synaptic activity originates from a group of oscillatory neurons lying within the lateral protocerebrum. Simultaneous intracellular recordings from many LPI pairs indicate that this periodic synaptic input is synchronous and coherent among the population of approximately 200 LPIs on each side of the brain. In many LPIs, specific odors applied to antennules in isolated head preparations generate long-lasting excitatory postsynaptic potentials and impulse bursts. The impulse bursts are generated only near the peaks of the ongoing depolarizations, approximately 1 s after stimulus application, and so the periodic baseline activity is instrumental in timing burst generation. Simultaneous recordings from pairs of LPIs show that, when impulse bursts occur in both cells after an odorant stimulus, they are synchronized by the common periodic depolarizations. We conclude that the common, periodic activity in LPIs can synchronize impulse bursts in subsets of these neurons, possibly generating powerful long-lasting postsynaptic effects in downstream target neurons. (+info)
Sympathetic neuronal oscillators are capable of dynamic synchronization.
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In this paper we show that the discharges of sympathetic neurons innervating an identified peripheral target are driven by multiple oscillators that undergo dynamic synchronization when an entraining force, central respiratory drive (CRD), is increased. Activity was recorded from postganglionic sympathetic neurons (PGNs) innervating the caudal ventral artery of the rat tail: (1) at the population level from the ventral collector nerve (VCN); and (2) from pairs of single PGNs recorded simultaneously using a focal recording technique. Autospectral analysis of VCN activity revealed a more prominent rhythmical component in the presence of CRD than in its absence, suggesting that (1) multiple oscillators drive the discharges of PGNs and (2) these oscillators can be entrained and therefore synchronized by CRD. This interpretation was supported by analysis of the firing behavior of PGN pairs. Autocorrelation and cross-correlation analysis showed that pairs were not synchronized in the absence of CRD but showed significant synchronization when CRD was enhanced. Time-evolving spectral analysis and raster plots demonstrated that the temporal stability of PGN-to-PGN and CRD-to-PGN interactions at a given level of CRD were also dynamic in nature, with stable constant phase relationships predominating as CRD was increased. This is the first reported example of dynamic synchronization in populations of single postganglionic sympathetic neurons, and we suggest that, as in sensory processing and motor control, temporal pattern coding may also be an important feature of neuronal discharges in sympathetic pathways. (+info)
Mechanisms of neural synchrony in the septohippocampal pathways underlying hippocampal theta generation.
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Using urethane-anesthetized rats, 18 simultaneously recorded septohippocampal cell pairs (36 individual cells), each classified as theta-related according to the criteria of, were studied during four spontaneously occurring hippocampal field conditions: (1) large amplitude irregular activity (LIA) only; (2) the transition from LIA to theta; (3) theta only; and (4) the transition from theta to LIA. The main objective was to study the temporal relationships and degree of neural synchrony between the discharges of the cell pairs, using both time-averaged and time-dependent joint peristimulus time histogram correlation techniques, during the four conditions, to determine their contribution to the control of oscillation and synchrony (theta) in the hippocampus. The study demonstrated that the transition from the LIA state to the theta field state in the hippocampus required a temporal sequence of changes in theta-related cellular activity occurring on average 500 msec preceding the transition: (1) the medial septum inhibits hippocampal theta-OFF cells; (2) medial septal tonic theta-ON cells provide tonic depolarizing inputs to initiate membrane potential oscillations (MPOs) in hippocampal phasic theta-ON cells, whereas medial septal phasic theta-ON cells synchronize the MPOs of hippocampal phasic theta-ON cells and the discharges of hippocampal tonic theta-ON cells. Much of the time preceding the LIA to theta transition is accounted for by recruitment of these theta-related cell populations. Conversely, "turning off" the theta state occurs abruptly and involves the medial septal disinhibition of hippocampal theta-OFF cells. (+info)
Synchronization between temporal and parietal cortex during multimodal object processing in man.
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A series of recordings in cat visual cortex suggest that synchronous activity in neuronal cell ensembles serves to bind the different perceptual qualities belonging to one object. We provide evidence that similar mechanisms seem also to be observable in human subjects for the representation of supramodal entities. Electroencephalogram (EEG) was recorded from 19 scalp electrodes (10/20 system) in 19 human subjects and EEG amplitude and coherence were determined during presentation of objects such as house, tree, ball. Objects were presented in three different ways: in a pictorial presentation, as spoken words and as written words. In order to find correlates of modality-independent processing, we searched for patterns of activation common to all three modalities of presentation. The common pattern turned out to be an increase of coherence between temporal and parietal electrodes in the 13-18 Hz beta1 frequency range. This is evidence that population activity of temporal cortex and parietal cortex shows enhanced coherence during presentation of semantic entities. Coherent activity in this low-frequency range might play a role for binding of multimodal ensembles. (+info)
Neuronal response synchronization with millisecond precision has been proposed to serve feature binding in vision and should therefore, like visual experience, depend on central states. Here we test this hypothesis by examining the occurrence and strength of response synchronization in areas 17 and 18 of anesthetized cats as a function of central states. These were assessed from the frequency content of the electroencephalogram, low power in the delta and high power in the gamma frequency ranges (here 20-70 Hz) being considered as a signature of activated states. We evaluated both spontaneous state changes and transitions induced by electrical stimulation of the mesencephalic reticular formation. During states of low central activation, visual responses were robust but lacked signs of precise synchronization. At intermediate levels of activation, responses became synchronized and exhibited an oscillatory patterning in the range of 70-105 Hz. At higher levels of activation, a different pattern of response synchronization and oscillatory modulation appeared, oscillation frequency now being in the range of 20-65 Hz. The strength of response synchronization and oscillatory modulation in the 20-65 Hz range increased with further activation and was associated with a decrease in oscillation frequency. We propose that the oscillatory patterning in the 70-105 Hz range is attributable to oscillatory retinothalamic input and that a minimal level of activation is necessary for cortical neurons to follow this oscillatory pattern. In contrast, the synchronization of responses at oscillation frequencies in the 20-65 Hz range appears to result from intracortical synchronizing mechanisms, which become progressively more effective as central activation increases. Surprisingly, enhanced synchronization and oscillatory modulation in the gamma frequency range were not associated with consistent increases in response amplitude, excluding a simple relation between central activation and neuronal discharge rate. The fact that intracortical synchronizing mechanisms are particularly effective during states of central activation supports the hypothesis that precise synchronization of responses plays a role in sensory processing. (+info)
Spatiotemporal analysis of local field potentials and unit discharges in cat cerebral cortex during natural wake and sleep states.
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The electroencephalogram displays various oscillation patterns during wake and sleep states, but their spatiotemporal distribution is not completely known. Local field potentials (LFPs) and multiunits were recorded simultaneously in the cerebral cortex (areas 5-7) of naturally sleeping and awake cats. Slow-wave sleep (SWS) was characterized by oscillations in the slow (<1 Hz) and delta (1-4 Hz) frequency range. The high-amplitude slow-wave complexes consisted in a positivity of depth LFP, associated with neuronal silence, followed by a sharp LFP negativity, correlated with an increase of firing. This pattern was of remarkable spatiotemporal coherence, because silences and increased firing occurred simultaneously in units recorded within a 7 mm distance in the cortex. During wake and rapid-eye-movement (REM) sleep, single units fired tonically, whereas LFPs displayed low-amplitude fast activities with increased power in fast frequencies (15-75 Hz). In contrast with the widespread synchronization during SWS, fast oscillations during REM and wake periods were synchronized only within neighboring electrodes and small time windows (100-500 msec). This local synchrony occurred in an apparent irregular manner, both spatially and temporally. Brief periods (<1 sec) of fast oscillations were also present during SWS in between slow-wave complexes. During these brief periods, the spatial and temporal coherence, as well as the relation between units and LFPs, was identical to that of fast oscillations of wake or REM sleep. These results show that natural SWS in cats is characterized by slow-wave complexes, synchronized over large cortical territories, interleaved with brief periods of fast oscillations, characterized by local synchrony, and of characteristics similar to that of the sustained fast oscillations of activated states. (+info)