Episodic multiregional cortical coherence at multiple frequencies during visual task performance

Abstract

THE way in which the brain integrates fragmentary neural events at multiple locations to produce unified perceptual experience and behaviour is called the binding problem^1,2. Binding has been proposed to involve correlated activity at different cortical sites during perceptuomotor behaviour^3–5, particularly by synchronization of narrow-band oscillations in the & gamma;-frequency range (30& ndash;80 Hz)^6,7. In the rabbit olfactory system, inhalation induces increased & gamma;-cor-relation 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 areas^9–12. In monkeys, some groups have found that & gamma;-oscillations transiently synchronize within striate cortex¹³, superior temporal sulcus¹⁴ and somatosensorimotor cortex^15,16. Others have reported that visual stimuli produce increased broad-band power, but not & gamma;-oscillations, in several visual cortical areas^17,18. But the absence of narrow-band oscillations in itself does not disprove interregional 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 intervening sites. Spatially selective multiregional cortical binding, in the form of broad-band synchronization, may thus play a role in primate perceptuomotor behaviour.