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

THE way in which the brain integrates fragmentary neural events at mul tiple locations to produce unified perceptual experience and behaviour is called the binding problem1,2. Binding has been proposed to involv e correlated activity at different cortical sites during perceptuomoto r behaviour3-5, particularly by synchronization of narrow-band oscilla tions in the gamma-frequency range (30-80 Hz)6,7. In the rabbit olfact ory system, inhalation induces increased gamma-correlation between sit es in olfactory bulb and cortex8. In the cat visual system, coherent v isual stimuli increase gamma-correlation between sites in both the sam e and different visual cortical areas9-12. In monkeys, some groups hav e found that gamma-ocillations transiently synchronize within striate cortex13, superior temporal sulcus14 and somatosensorimotor cortex15,1 6. 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 di sprove inter-regional synchronization, which may be a broad-band pheno menon. We now describe episodes of increased broad-band coherence amon g local field potentials from sensory, motor and higher-order cortical sites of macaque monkeys performing a visual discrimination task. Wid ely distributed sites become coherent without involving other interver ting sites. Spatially selective multiregional cortical binding, in the form of broad-band synchronization, may thus play a role in primate p erceptuomotor behaviour.