Academic journal article Psychology in Russia

Frequency-Selective Gamma Generators in Processing of Auditory Stimuli

Academic journal article Psychology in Russia

Frequency-Selective Gamma Generators in Processing of Auditory Stimuli

Article excerpt

Abstract

Processing of sensory stimuli is controlled by the top-down influences that shape oscillations in the synchrony form revealed in the EEG. However, little is known about the nature of these influences. The present study investigated the contribution of "evoked oscillations" in the perception of auditory stimuli during passive and active attention from the position of pacemaker hypothesis on the origin of gamma rhythm. To analyze the problem, the author suggests a special method based on the narrow frequency filtering event-related potentials, localization of dipole sources of gamma oscillations over the structural MRI slices. Computation of equivalent dipoles for the discrete frequencies demonstrates interaction between prefrontal and auditory cortex during active attention to auditory stimuli. The obtained results are compatible with the pacemaker hypothesis.

DOI: 10.11621/pir.2008.0019

Pages: 299-308

By: Danilova, Nina N.

Themes: Psychophysiology

Keywords: psychophysiology, methodology

High-frequency electrical brain activity, gamma rhythm, is associated with intense mental activity and cognitive function in general. It is connected with perception, awareness, response to novelty, voluntary and involuntary attention and memory (Eckhorn et al., 1990; Lutzenberger, W., Pulvermul-ler, F., Birbaumer, N., 1994; Pulvermuller, F., Preissl, H., Lutzenberger, W. and Birbaumer, N., 1995; Singer, 1999; Danilova, 2000; Danilova, Bykova, Anisimov, Pirogov, Sokolov, 2002; Tallon-Baudry, Bertrand, O., Bouchet, P. and Pernier, J. 1995; Tallon-Baudry C, Kreiter A., Bertrand O., 1999).

Inclusion of gamma oscillations into different sensory, cognitive, performing processes, its existence not only in human, but also in animal brain allowed E. Basar (Basar, 1999; Basar-Eroglu, Karakas, Shurman, 2001) to consider gamma-rhythm as functional building blocks used in integration of brain processes and realization of psychical functions.

Under increased interest in gamma oscillations many questions are still to be answered. For example, mechanism of gamma oscillation origin is not clear. There are two basic conceptions about mechanisms of gamma rhythm generation: binding hypothesis and pacemaker hypothesis.

According to the binding hypothesis gamma rhythm is resulted in circulation of impulses within neuronal assembly. Oscillatory activity in the neuronal assemblies appeared by means feedback and reciprocal loops among its neurons. The pacemaker hypothesis suggests existence of pacemaker neurons as intracellular generators of gamma oscillations. Pacemaker neurons are characterized by next properties:

The endogenous rhythmical activity in pacemaker neurons did not disappear after absolute isolation of pacemaker neurons from contacts with others neurons (Grechenko, 1999). The impotent characteristic of pacemaker neuron - its response to input stimuli. Excitatory inputs to these neurons can produce phase shift (reset) of endogenous oscillations phase-locked to input stimuli.

Thus, the assembly hypothesis of gamma rhythm origin assumes presence at least two spatially separate centers of activity and signal transmission from one center to other. According to pacemaker hypothesis such mechanism of signal transmission is not required.

To testing pacemaker hypothesis of gamma oscillations origin we investigated "evoked" gamma rhythm as well compatible with pacemaker neuron properties during the perception of auditory stimuli in the conditions of passive and active attention.

The new experimental approach was developed for this aim - the method of microstructure analysis of gamma rhythm (Danilova, 2000, 2006) that includes:

1. Narrow band frequency filtering of event-related potentials (with 1 Hz step) in the gamma range between 30 and 75 Hz.

2. Computation of equivalent dipole sources for discrete frequencies in gamma range.

3. Combination equivalent dipole analysis with structural MRI. …

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