EPISODIC MULTIREGIONAL CORTICAL COHERENCE AT MULTIPLE FREQUENCIES DURING VISUAL TASK-PERFORMANCE

THE way in which the brain integrates fragmentary neural events at multiple locations to produce unified perceptual experience and behaviour is called the binding problem1,2. Binding has been proposed to involve correlated activity at different cortical sites during perceptuomotor behaviour3-5, particularly by synchronization of narrow-band oscillations in the gamma-frequency range (30-80 Hz)6,7. In the rabbit olfactory system, inhalation induces increased gamma-correlation between sites in olfactory bulb and cortex8. In the cat visual system, coherent visual stimuli increase gamma-correlation between sites in both the same and different visual cortical areas9-12. In monkeys, some groups have found that gamma-ocillations transiently synchronize within striate cortex13, superior temporal sulcus14 and somatosensorimotor cortex15,16. Others have report that visual stimuli produce increased broad-band power, but not gamma-oscillations, in several visual cortical areas17,18. But the absence of narrow-band oscillations in itself does not disprove inter-regional synchronization, which may be a broad-band phenomenon. We now describe episodes of increased broad-band coherence among local field potentials from sensory, motor and higher-order cortical sites of macaque monkeys performing a visual discrimination task. Widely distributed sites become coherent without involving other interverting sites. Spatially selective multiregional cortical binding, in the form of broad-band synchronization, may thus play a role in primate perceptuomotor behaviour.