Biomedical subjects

Boris Gourévitch

Publications and source records attributed to Boris Gourévitch.

5 recordsLinked to original sources

PubMed2007

Evaluating information transfer between auditory cortical neurons.

Transfer entropy, presented as a new tool for investigating neural assemblies, quantifies the fraction of information in a neuron found in the past history of another neuron. The asymmetry of the measure allows feedback evaluations. In particular, this tool has potential applications in investigating windows of temporal integration and stimulus-induced modulation of firing rate. Transfer entropy is also able to eliminate some effects of common history in spike trains and obtains results that are different from cross-correlation. The basic transfer entropy properties are illustrated with simulations. The information transfer through a network of 16 simultaneous multiunit recordings in cat's auditory cortex was examined for a large number of acoustic stimulus types. Application of the transfer entropy to a large database of multiple single-unit activity in cat's primary auditory cortex revealed that most windows of temporal integration found during spontaneous activity range between 2 and 15 ms. The normalized transfer entropy shows similarities and differences with the strength of cross-correlation; these form the basis for revisiting the neural assembly concept.

Acoustic Stimulation↗

PubMed2006

A nonparametric approach for detection of bursts in spike trains.

In spike-train data, bursts are considered as a unit of neural information and are of potential interest in studies of responses to any sensory stimulus. Consequently, burst detection appears to be a critical problem for which the Poisson-surprise (PS) method has been widely used for 20 years. However, this method has faced some recurrent criticism about the underlying assumptions regarding the interspike interval (ISI) distributions. In this paper, we avoid such assumptions by using a nonparametric approach for burst detection based on the ranks of ISI in the entire spike train. Similar to the PS statistic, a "Rank surprise" (RS) statistic is extracted. A new algorithm performing an exhaustive search of bursts in the spike trains is also presented. Compared to the performances of the PS method on realizations of gamma renewal processes and spike trains recorded in cat auditory cortex, we show that the RS method is very robust for any type of ISI distribution and is based on an elementary formalization of the definition of a burst. It presents an alternative to the PS method for non-Poisson spike trains and is simple to implement.

Action Potentials↗

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↗

PubMed2006

Linear and nonlinear causality between signals: methods, examples and neurophysiological applications.

In this paper, we will present and review the most usual methods to detect linear and nonlinear causality between signals: linear Granger causality test (Geweke in J Am Stat Assoc 77:304-313, 1982) extended to direct causality in multivariate case (LGC), directed coherence (DCOH, Saito and Harashima in Recent advances in EEG and EMG data processing, Elsevier, Amsterdam, 1981), partial directed coherence (PDC, Sameshima and Baccala 1999) and nonlinear Granger causality test of Baek and Brock (in Working Paper University of Iowa, 1992) extended to direct causality in multivariate case (partial nonlinear Granger causality, PNGC). All these methods are tested and compared on several ARX, Poisson and nonlinear models, and on neurophysiological data (depth EEG). The results show that LGC, DCOH and PDC are not very robust in relation to nonlinear linkages but they seem to correctly find linear linkages if only the autoregressive parts are nonlinear. PNGC is extremely dependent on the choice of parameters. Moreover, LGC and PNGC may give misleading results in the case of causality on a spectral band, which is illustrated by our neurophysiological database.

Animals↗

PubMed2006

Spectrally enhanced acoustic environment disrupts frequency representation in cat auditory cortex.

Sensory environments are known to shape nervous system organization. Here we show that passive long-term exposure to a spectrally enhanced acoustic environment (EAE) causes reorganization of the tonotopic map in juvenile cat auditory cortex without inducing any hearing loss. The EAE consisted of tone pips of 32 different frequencies (5-20 kHz), presented in random order at an average rate of 96 Hz. The EAE caused a strong reduction of the representation of EAE frequencies and an over-representation of frequencies neighboring those of the EAE. This is in sharp contrast with earlier developmental studies showing an enlargement of the cortical representation of EAEs consisting of a narrow frequency band. We observed fewer than normal appropriately tuned short-latency responses to EAE frequencies, together with more common long-latency responses tuned to EAE-neighboring frequencies.

Acoustic Stimulation↗