Reduced Synchronization in the Visual Cortex of Cats with Strabismic Amblyopia

Abstract

Synchronous firing of spatially separate neurons was studied with multi-electrode recordings in area 17 of the visual cortex of strabismic cats which had developed behaviourally verified amblyopia of the deviated eye. Responses of neurons were evoked with moving light bars or gratings of different spatial frequency. Neurons driven by the normal eye displayed stronger synchronization of their responses than neurons dominated by the amblyopic eye. These interocular differences were highly significant and particularly pronounced for grating stimuli of high spatial frequency. No interocular differences were noted with respect to the amplitudes of responses to the light bars and gratings. These results suggest reduced synchronization of population responses as a neurophysiological correlate of strabismic amblyopia and underline the importance of correlated firing of spatially separate cortical neurons for normal processing of visual information.

Temporal Binding, Binocular Rivalry, and Consciousness

“…Taken together, these experiments demonstrate that Gestalt criteria such as continuity or coherent motion, which have psychophysically been shown to support perceptual grouping, are important for the establishment of precise synchrony among neurons in the visual cortex. These data strongly support the Roelfsema et al 1994) hypothesis that correlated firing provides a dynamic mechanism for feature binding and response selection.…”

“…Clearly, at least some of these deficits indicate a reduced capacity of integrating visual information and an impairment of the mechanisms responsible for feature binding. The results of the correlation study by Roelfsema et al (1994) indicate that these perceptual deficits may be due to a disturbance of intracortical interactions (see figure 8.2). Thus, clear di¤erences were observed in the synchronization of cells driven by the normal and the amblyopic eye, respectively.…”

“…Additional evidence that neuronal synchronization is indeed functionally relevant and related to the animal's perception is provided by experiments on cats with convergent squint (Roelfsema et al 1994). Subjects with this type of strabismus often use only one eye for active fixation.…”

Asynchronous inputs alter excitability, spike timing, and topography in primary auditory cortex

“…The normally distinct digit representations were also integrated together after extensive operant training with stimuli that simultaneously activate several fingers (Wang et al, 1995). In primary visual cortex, both strabismus and alternating electrical stimulation of the optic nerves disrupt the normally high correlation between the eyes and increase the segregation of inputs from each eye (Eschweiler and Rauschecker, 1993;Hubel and Wiesel, 1965;Roelfsema et al, 1994;Stryker and Strickland, 1984). These and other results suggest that simultaneous activation of neural networks leads to greater integration of sensory inputs, while asynchronous activation leads to segregation (Clark et al, 1988;Constantine-Paton and Law, 1978;Hubel and Wiesel, 1965;Stryker and Strickland, 1984;Wang et al, 1995).…”

The Relationship Between Synchronization Among Neuronal Populations and Their Mean Activity Levels

“…Clearly, desynchronization between two dynamic cell assemblies is not only a possibility but can be observed in both the real brain and simulations where changes in synchrony have, in some instances, been found to occur without any change in mean ring rate. Such regional decoupling of spike timing and ring rates has been reported in primary sensory cortices (Roelfsema, Konig, Engel, Sireteanu, & Singer, 1994;deCharms & Merzenich, 1996;Fries, Roelfsma, Engel, Konig, & Singer, 1997) and may re ect feedback in uences from higher cortical areas (Lumer et al, 1997b). Our input stimulus consisted of unstructured random noise that did not have any spatiotemporal structure.…”