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It has recently been suggested that reentrant connections are essential in systems that process complex information [A. Damasio, H. Damasio, Cortical systems for the retrieval of concrete knowledge: the convergence zone framework, in: C. Koch, J.L. Davis (Eds.), Large Scale Neuronal Theories of the Brain, The MIT Press, Cambridge, 1995, pp. 61-74; G. Edelman, The Remembered Present, Basic Books, New York, 1989; M.I. Posner, M. Rothbart, Constructing neuronal theories of mind, in: C. Koch, J.L. Davis (Eds.), Large Scale Neuronal Theories of the Brain, The MIT Press, Cambridge, 1995, pp. 183-199; C. von der Malsburg, W. Schneider, A neuronal cocktail party processor, Biol. Cybem., 54 (1986) 29-40]. Reentry is not feedback, but parallel signalling in the time domain between spatially distributed maps, similar to a process of correlation between distributed systems. Accordingly, it was expected that during spontaneous reversals of the Necker cube, complex patterns of correlations between distributed systems would be present in the cortex. The present study included EEG (n=4) and MEG recordings (n=5). Two experimental questions were posed: (1) Can distributed cortical patterns present during perceptual reversals be classified differently using a generalised regression neural network (GRNN) compared to processing of a two-dimensional figure? (2) Does correlated cortical activity increase significantly during perception of a Necker cube reversal? One-second duration single trials of EEG and MEG data were analysed using the GRNN. Electrode/sensor pairings based on cortico-cortical connections were selected to assess correlated activity in each condition. The GRNN significantly classified single trials recorded during Necker cube reversals as different from single trials recorded during perception of a two-dimensional figure for both EEG and MEG. In addition, correlated cortical activity increased significantly in the Necker cube reversal condition for EEG and MEG compared to the perception of a non-reversing stimulus. Coherent MEG activity observed over occipital, parietal and temporal regions is believed to represent neural systems related to the perception of Necker cube reversals., (Copyright 1998 Elsevier Science B.V.)

Recent work provides clues that different cortical mechanisms may be employed when correcting for errors in sensorimotor synchronization that increase tap-tone asynchrony compared with those that decrease it. The authors tested this hypothesis by recording 64-channel electroencephalography while participants synchronized with an auditory metronome. We systematically introduced positive and negative phase-shift perturbations that were either liminal (10%) and subliminal (3%). We used a distributed source modeling approach to evaluate oscillatory activity and connectivity of discrete cortical sources. Three key findings support our hypothesis. First was a theta band response indicative of error detection and top-down control observed in frontomedial presupplementary motor area (pre-SMA) and anterior cingulate for liminal positive perturbations. Second was an increase in theta band coupling between the SMA and contralateral motor cortex exclusively for positive perturbations suggesting a top-down modulation of motor parameters. Third, when compared with other conditions, liminal positive perturbations result in an increase in postmovement beta rebound within contralateral primary motor cortex. The authors propose that frontomedial motor areas exert a top-down inhibitory influence over the primary motor cortex to effectively lengthen tap intervals in response to lengthening tap-tone asynchronies. [ABSTRACT FROM AUTHOR]