Neural mechanisms of scene segmentation: recordings from the visual cortex suggest basic circuits for linking field...

Synchronization of neural activity has been proposed to code feature linking. This was supported by the discovery of synchronized neural activities in cat and monkey visual cortex which occurred stimulus dependent either oscillatory (30-100 Hz) or nonrhythmical, internally generated or stimulus dominated. The area in visual space covered by receptive fields of an actually synchronized assembly of neurons was termed the "linking field." The present paper aims at relating signals of stimulus dependent synchronization and desynchronization, observed by us in the visual cortex of monkeys, with models of basic neural circuits explaining the measured signals and extending our former linking field model. The circuits include: 1) a model neuron with the capability of fast mutual spike linking and decoupling which does not degrade the receptive field properties; 2) linking connections for fast synchronization in neighboring assemblies driven by the same stimulus; 3) feedback inhibition in local assemblies via a common interneuron subserving synchronization, desynchronization, and suppression of uncorrelated signals; and 4) common-input connectivity among members of local and distant assemblies supporting zero-delay phase difference in distributed assemblies. Other recently observed cortical effects that potentially support scene segmentation are shortly reviewed to stimulate further ideas for models. Finally, the linking field hypothesis is critically discussed, including contradictory psychophysical work and new supportive neurophysiological evidence.