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Ventral sector of zona incerta (ZIv) was postulated to provide a significant GABA-ergic input to the higher-order thalamic nuclei. The aim of this study was to characterize, at the population level, the electrical activity evoked by a whisker stimulation in ZIv. In anesthetized rats microelectrodes were positioned into several locations encompassing ZI. EPs were recorded in response to deflection of mystacial vibrissae. The strongest response occurred in the posteriomedial part of ZIv with EPs starting at 3 ms post-stimulus with a large phasic negative wave followed by two low-amplitude slow positive and negative waves. The known connectivity of ZI suggest that short latency negative waves result from glutamatergic input from the spinal trigeminal nuclei, whereas longer-latency negative waves could originate from the cortical projections. Positive waves might reflect the activation of inhibitory input from anterior pretectal nucleus. Supported by the polish National Science Centre grant N N401 533040.
Local fi eld potential (LFP) – the result of summed postsynaptic potentials from cell populations – reveal the most characteristic neural activity at the recording site in the brain. Thus LFPs are well suited for study of neural networks, specifi cally those involved in processing of sensory information. We propose a method of assessing functional brain connectivity through LFP analysis. The method is applied to multi-site signals representing potentials evoked by a repeated, stereotyped stimulus. In spite of a stereotyped stimulus, all responses are different due to, inter alia, ongoing background activity of the brain and this trial-to-trial variability is utilized in our analysis. The method is based on calculation of correlations between trial-to-trial LFP variations at every post-stimulus latency at every recoding site. The results show how neuronal activities at different sites and latencies correspond to activation at other sites with a given time delays. We used this method to analyze the functional connectivity in thalamocortical network involved in processing of somatosensory (vibrissal) information in non-anaesthetised rat. One result is that the cortical activation at 25–50 ms post-stimulus correlates with thalamic LFP measured at 50–150 ms post stimulus, thus implying this late latency thalamic activity depends on a corticothalamic feedback. Apart from raw LFP, the method is applicable to results of various decomposition methods of brain signals (PCA, ICA, etc.)
We investigated the dynamics of gamma oscillations in thalamo-cortical part of the rat vibrissa-barrel system. LFPs were recorded by multiwire arrays implanted chronically in the barrel cortex and somatosensory thalamus in non-anesthetized rats at two arousal levels: quiescence (induced by long lasting habituation process) and arousal (elicited by contextual aversive stimuli). As compared to quiescence, in an aroused state we observed enhancement of power in gamma frequency (45–90 Hz) band arranged in a specific temporal pattern: the high gamma (73–90 Hz) bursts appeared ca. 230 ms after stimulus onset and developed into the lower gamma (53–73 Hz) activity at ~300 ms after stimulus. The effect was observed in 7 out of 14 examined sessions (in four animals) in which novelty component was raised by the first introduction of new arousing stimuli. Research supported by the Polish National Science Centre grant N N401-533040
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