Functional connectivity in auditory cortex using chronic, multichannel unit recordings.
ABSTRACT Chronic, multichannel recordings provide a method for reliable detection and determination of long-term dynamic functional connectivity. Using chronically implanted multichannel electrode arrays, we simultaneously recorded 30–70 units in guinea pig auditory cortex in daily recording sessions for implant durations of six months. We examined stimulus response properties and correlation strengths in neuron pairs in four animals. Preliminary results from these `snapshots’ of functional connectivity suggest sparse functional connections among widely distributed neurons. Some of these functional connections were found to persist for several days. These results provide a framework upon which further investigations of functional dynamic connectivity can be developed.
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ABSTRACT: The activities of several single units (6-10) were recorded simultaneously in the auditory cortex and in frontal cortical areas of cats and monkeys. The response properties of the single units and the interaction between them were studied. It is shown that single units in both areas may participate in prolonged processes and be involved in more than one process. Adjacent neurons need not function in unison; while some neurons are activated, others may stay inactive. The interactions among adjacent neurons are weak, and can be modulated by sensory stimulation, and by arousal and behavioral states. These properties lead us to hypothesize that information is represented in the cortex by coactivation of sets of neurons rather than by independent modulation of the single-unit firing rate. A single unit may be a member of several representing sets. Thus, each neuron may participate in more than one function and each small cortical area may contain members of several functional sets. A mechanism for computing and transmitting information, based on converging-diverging links, between neuronal sets is described and tested by simulations and analysis of experimental data.IEEE Transactions on Biomedical Engineering 02/1989; 36(1):25-35. · 2.35 Impact Factor
Article: Neuronal assemblies.[show abstract] [hide abstract]
ABSTRACT: This paper examines the concept of neuronal assembly as it has appeared in selected portions of the literature. The context is experimental access to real neuronal assemblies in working brains, as made possible by recent technological progress. One current measure of assembly organization is based on correlation of firing among neurons; recent observations show that such correlations can vary rapidly. In this paper, we demonstrate that dynamic firing correlation can be caused either by dynamic changes in neuronal connection strengths or, alternatively, by the effects of an unobserved (large) pool of other neurons. The static connectivity within the pool appears to be important in determining these effects.IEEE Transactions on Biomedical Engineering 02/1989; 36(1):4-14. · 2.35 Impact Factor
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ABSTRACT: Simultaneous extracellular recordings from one electrode of 'local' groups of 3-6 neurons were obtained from the auditory cortex of unanesthetized, paralyzed cats. The activity and functional connectivity of local microenvironments were examined under various auditory stimuli. Single cell response patterns were examined using peri-stimulus (PST) histograms and functional connectivity among neighboring cells by the cross renewal density (CRD) histograms. Analysis of the PST histograms suggested that a high percentage of single cells demonstrated different response patterns to different stimuli. Analysis of the CRD histograms suggested, on the one hand, that only small numbers of neighboring cells behaved as if there were direct connections from one cell to another, and that these direct connections appeared to be excitatory. On the other hand, many cell pairs shared input from shared sources which lay outside the local groups. The majority of functional connections were altered by at least one of the stimuli delivered, thus demonstrating the system's plasticity. It is suggested that long-term gates at the synaptic level are responsible for this phenomenon.Brain Research 09/1983; 272(2):211-21. · 2.88 Impact Factor