Neuronal Synchronization in the Visual Cortex of the Alert State

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An important part of vision is pattern recognition, so that a visual scene that contains many combinations of visual features is perceived as a coherent collection of objects. Sets of local features making up the objects in an image must be grouped according to some criteria and segregated from one another to prevent inappropriate feature conjunctions. The pattern of images falling on the retina of the eye is encoded by many thousands of nerve cells sending signals into the brain, and it is not clear how the brain integrates the information that is sent to different parts of the visual cortex. One alternative commonly accepted is that some neurons are selectively responsive to certain features of a stimulus, and the outputs from these neurons, even from widely separate areas, converge on other cells that represent "feature detectors" in a hierarchical organization of complex processing. An alternative that has recently been raised is that the integrated features that make up objects are coded by a distributed population of neurons that share synchronous activity. There is some evidence for both processes, but the mechanisms underlying the latter remain unclear. Synchrony has been observed in some cases in the visual cortex of cats and monkeys. This study determines the incidence, properties and spatial extent of neuronal synchronous firing of neurons in the visual cortex of alert animals trained to fixate their eyes on a target object. A novel multiple electrode array records the simultaneous responses of several single cells to a variety of different visual stimuli. These recordings allow tests of how well responses from different cells are correlated, and to what degree synchronous activity is present among cells in several different cortical areas. Results will be important for understanding cortical function, for sensory neuroscience and perceptual psychology in general, and for potential use in the engineering design of artificial visual systems.