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ABSTRACT: Models of brain function predict that the recurrence of a process or state will be reflected in repeated patterns of correlated activity. Previous work on medullary raphe assembly dynamics revealed transient changes in impulse synchrony. This study tested the hypothesis that these variations in synchrony include distributed nonrandom patterns of association. Spike trains were recorded simultaneously in the ventrolateral medulla, n. raphe obscurus, and n. raphe magnus of four anesthetized (Dial), vagotomized, paralyzed, and artificially ventilated adult cats. The "gravitational" representation of spike trains was used to detect moments of impulse synchrony in neuronal assemblies visualized as variations in the aggregation velocities of particles corresponding to each neuron. Template matching algorithms were developed to identify excessively repeating patterns of particle condensation rates. Repeating patterns were detected in each animal. The reiterated patterns represented an emergent property not apparent in either corresponding firing rate histograms or conventional gravity representations. Overlapping subsets of neurons represented in different patterns were unmasked when the template resolution was changed. The results demonstrate repeated transient network configurations defined by the tightness and duration of synchrony in different combinations of neurons and suggest that multiple information streams are conveyed concurrently by fluctuations in the synchrony of on-going activity.
Journal of Neurophysiology 10/1997; 78(3):1714-9. · 3.32 Impact Factor
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ABSTRACT: 1. The initial objective of this study was to determine whether respiratory-related neural assemblies exist in the brain stem midline. A second goal was to seek evidence for concurrent relationships among the neurons that could generate the detected synchrony. 2. Experiments were conducted on anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Spike trains of four to nine simultaneously monitored neurons were recorded in the regions of n. raphe obscurus-n. raphe pallidus and n. raphe magnus. 3. Data were analyzed with cycle-triggered histograms, cross-correlograms, snowflakes, and the gravitational representation. A significance test for the gravity method was developed and tested with spike trains generated by simulated networks with defined connections. 4. Ninety-three groups of neurons from 24 cats were studied. Thirty-nine groups from 19 cats included neurons that discharged synchronously on a millisecond time scale; less than or equal to 19 pairs of synchronously discharging neurons were found in one group. Twenty-seven of these 39 groups included neurons that had respiratory-modulated firing rates and discharged synchronously with other group members. Synchronous assemblies included cells monitored at rostral or caudal locations, or both. 5. Six classes of relationships were inferred from groups of neurons with multiple correlations: divergence (n = 11); convergence (n = 7); connections with opposite actions between neurons (n = 5); projections of synchronous neurons to separate targets (n = 5); projections to one neuron in a synchronous group (n = 4); and projections between two synchronous groups with common elements (n = 6). 6. The results document the existence of assemblies of synchronously discharging respiratory-related neurons in midline regions of the brain stem and suggest that divergent excitatory and inhibitory connections within the midline participate in the generation of that synchrony. Links between assemblies may operate to stabilize their collective activity in a particular state.
Journal of Neurophysiology 05/1992; 67(4):905-22. · 3.32 Impact Factor
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ABSTRACT: 1. The objective of this work was to determine whether configurations of midline brain stem neural assemblies change during the respiratory cycle. 2. Spike trains of several single neurons were recorded simultaneously in anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Data were analyzed with cross-correlational and gravity methods. 3. Sequential samples from each of eight groups of neurons known to contain synchronously discharging neurons exhibited temporal variations in that synchrony. 4. Gravity analysis of short (less than 200-s) samples of spike train data revealed 20 pairs of clustered particles that were not predicted from cross-correlation analysis of the parent data sets (greater than 20 min). 5. Twenty-nine groups of three to eight simultaneously monitored neurons, each with at least two synchronously discharging neurons, were analyzed for evidence of respiratory phase-dependent modulation of that coordinated activity. Spikes from successive interleaved inspiratory and expiratory intervals were analyzed separately. 6. Neurons pairs in 11 groups were more synchronous during the inspiratory interval; six groups had pairs that were more synchronous during the expiratory period. In two groups, different pairs were synchronous in different respiratory phases. In 11 of the 26 pairs that exhibited phase-dependent differences in synchrony, neither neuron had a respiratory-modulated firing rate as judged by either the cycle-triggered histogram or an analysis of variance of their firing rates. 7. Configurations of respiratory-related brain stem neural networks changed with time and the phases of breathing. Neurons with no apparent respiratory modulation of their individual firing rates collectively exhibited respiratory phase-dependent modulation of their impulse synchrony.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal of Neurophysiology 05/1992; 67(4):923-30. · 3.32 Impact Factor
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ABSTRACT: Experiments designed to study concurrent processes in neural networks have been hampered by limitations of available analytical methods. A recently described gravitational representation of spike train data was used to evaluate groups of simultaneously monitored medullary respiratory related neurons in anesthetized, vagotomized cats. The results establish that the method can detect and define functional associations among elements of such groups after as few as 20 respiratory cycles.
Brain Research 05/1989; 483(2):373-8. · 2.73 Impact Factor
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ABSTRACT: 1. Action potentials of crayfish claw motor neurons were recorded during both imposed constant-velocity displacements and imposed alternating sequences of opening and closing step movements of the dactyl. 2. Peristimulus time (PST) histograms show that the firing probabilities of two neurons, the opener inhibitor (OI) and the slow closer excitor (CE) consistently increased during opening ramp movements and declined during closing ramp movements. Hyperpolarizing synaptic potentials were observed in both cells during closing movements. 3. The proprioceptive field organizations of OI and CE were analyzed with response planes and contour planes. Each PST histogram in a plane displays the firing probability of the neuron as a function of time following step displacements at a given position. A relatively uniform early primary response followed each successive opening step. The probability of occurrence of later activity, when present, usually became more pronounced as the joint angle increased. Often both cells were silent during closing steps; when the cells were active, their firing probabilities were highest at the more open joint angles. 4. When both OI and CE were active, their spike trains were usually temporally correlated. 5. The other claw efferents did not respond to imposed movements in a consistent manner. When CE was active it was most likely to respond to closing movements near the closed position. 6. It is concluded that OI and CE are strongly and similarly influenced by proprioceptive reflexes. The responses of the two cells to imposed dactyl movements change as a function of joint angle, time after movement, and direction of movement.
Journal of Neurophysiology 04/1979; 42(2):368-82. · 3.32 Impact Factor
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ABSTRACT: 1. Action potentials of crayfish propodite-dactyl (PD) chordotonal organ receptors and two claw motor neurons, the opener inhibitor (OI) and slow closer excitor CE) were simultaneously monitored during imposed step and ramp movements of the dactyl or while the dactyl was held at various positions. 2. The activities of the cells during imposed displacements were analyzed using peristimulus time histograms and response and contour planes. The proprioceptive fields (PFs) of individual receptors resemble components of the more complex motor neuron PFs. Some receptors are briefly active after each successive opening step, while others do not respond to steps near the closed position but respond as the joint angle increases, becoming active when the claw is held open. Another type of receptor responds to closing movements. 3. Interactions among the various types of receptors and the two motor neurons were detected and analyzed by various statistical methods and intracellular recording techniques. The results indicate that receptors activated during opening movements and when the dactyl is held at open positions excite OI and CE via divergent functional connections. The efficacies of the connections made by a receptor may differ. Receptors activated by closing movements produce hyperpolarizing synaptic potentials in both efferents, possible directly or via interneurons. 4. It is concluded that several types of chordotonal organ receptors form an ensemble of parallel input channels, which modulates the activities of OI and CE and contributes to the generation of the spatial-temporal nonuniformities of their proprioceptive reflex responses.
Journal of Neurophysiology 04/1979; 42(2):383-99. · 3.32 Impact Factor
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Brain Research 08/1977; 130(2):348-53. · 2.73 Impact Factor
