Coherent oscillations: A mechanism of feature linking in the visual cortex?

Abstract

Primary visual coding can be characterized by the receptive field (RF) properties of single neurons. Subject of this paper is our search for a global, second coding step beyond the RF-concept that links related features in a visual scene. In recent models of visual coding, oscillatory activities have been proposed to constitute such linking signals. We tested the neurophysiological relevance of this hypothesis for the visual system. Single and multiple spikes as well as local field potentials were recorded simultaneously from several locations in the primary visual cortex (A17 and A18) using 7 or 19 individually advanceable fiber-microelectrodes (250 or 330 microns apart). Stimulus-evoked (SE)-resonances of 35-85 Hz were found in these three types of signals throughout the visual cortex when the primary coding channels were activated by their specific stimuli. Stimulus position, orientation, movement direction and velocity, ocularity and stationary flicker caused specific SE-resonances. Coherent SE-resonances were found at distant cortical positions when at least one of the primary coding properties was similar. Coherence was found 1) within a vertical cortex column, 2) between neighbouring hypercolumns, and 3) between two different cortical areas. We assume that the coherence of SE-resonances is mediated by recurrent excitatory intra- and inter-areal connections via phase locking between assemblies that represent the linking features of the actual visual scene. Visually related activities are, thus, transiently labelled by a temporal code that signalizes their momentary association.

The complementary brain: unifying brain dynamics and modularity

“…Indeed, relative activities need to be computed synchronously, and early theorems about short-term memory and long-term memory processing 67 predicted an important role for synchronous processing between the interacting cells. Subsequent neurophysiological experiments have emphasized the functional importance of synchronous brain states 86,87 . More recent neural modeling has shown how such synchronized activity patterns can, for example, quantitatively explain psychophysical data about temporal order judgments during perceptual grouping within the visual cortex 88 .…”

Prefrontal cortex and sensory cortices during working memory: quantity and quality

“…Besides the above studies linking alpha oscillations with WM quantity, two new studies have indicated their role in WM precision [70,71] , so it cannot be ruled out that alpha oscillations are also correlated with WM quality. Future studies to disentangle the roles of alpha power and phase would help to answer this question, since it has been shown that the phase-locked and non-phaselocked parts of alpha oscillations are related to different processes during WM [72] .Gamma synchronization was first found to subserve perceptual binding [73,74] . Recently, this synchronization has been suggested to be critical to WM (see reviews [75,76] ).…”

Oscillatory Brain Dynamics, Wavelet Analysis, and Cognition

“…For further studies of evoked electric and magnetic 40-Hz activity see, e.g., Galambos, Makeig, & Talmachoff (1981), Pantev et al (1991), and Ribary et al (1992). A large number of studies at the single-cell level complement these results (Llinás, 1988;Gray & Singer, 1987;Gray, König, Engel, & Singer, 1989;Eckhorn et al, 1988). The concept of evoked and induced rhythms ) is a further approach parallel to frequency analysis and resonance phenomena.…”

“…This statement is strongly based on cognitive experiments by means of single and multiple unit activity and field potentials in animals, event related potentials and EEG in humans, and a great variety of clinical studies by use of modern imaging techniques. The distributed alpha responses as reported here may add a further aspect to this problem which has so far been dominated by the widely discussed role of gamma responses for this process of perceptual binding (Gray & Singer, 1987;Gray et al, 1989;Eckhorn et al, 1988; for an overview including results at the EEG level, see, e.g., .…”