Dynamics of Neuronal Interactions in the Visual Cortex of Macaca Mulatta

This work is dedicated to studying the effects of attention which result in measurable changes in the functioning of single neurons and neuronal populations. A special emphasis lies on establishing a suitable method of recording from multiple neuronal populations in the visual cortex of a behaving monkey, as well as on analyzing the acquired signals. A chronically implanted large-area electrode array was used for epidural recording of brain potentials. Additionally, two electrode arrays for large-area chronic intracortical recording were designed, manufactured, and successfully implemented on a macaque monkey. By this means, local field potentials were recorded from different neuronal populations in two visual areas of a macaque monkey as he performed a shape-tracking task presented in front of him on a screen. Two kinds of stimulus-driven neuronal response in areas V1 and V4 were acquired: with the stimulus being behaviorally relevant and hence lying within the locus of the monkeya s attention, and with the stimulus being ignored and hence lying outside the locus of the monkeya s attention. Comparing the two response types provided a clue to the differences in neuronal processing of attended and non-attended stimuli. According to the working hypothesis, oscillatory responses generated in different neuronal populations by an attended stimulus would be synchronized in the gamma frequency band. To test this hypothesis, the acquired brain potentials were wavelet transformed and oscillatory power of different neuronal populations as well as phase coherence between them was computed. The results revealed a high degree of phase coherence in the gamma frequency band between oscillatory responses of neuronal populations in areas V1 and V4 representing the attended stimulus. A non-attended stimulus, however, produced non-phase-locked oscillatory responses in areas V1 and V4. The results presented here supported the working hypothesis, and the gamma-band synchronization was suggested to provide the mechanism of attention which enhances the processing of behaviorally relevant stimuli.