Peter Konig, Astrid von Stein and Carl Chiang
The Neurosciences Institute, San Diego
Findings on visual cortical interaction indicate that functional assemblies of neurons can be formed by synchronous firing. So far this synchronization has been shown to be stimulus - induced and reflecting stimulus properties. If, however, synchronization relates to perception, the synchronization pattern should as well reflect the behavioral relevance and the cat's expectancy.
Indeed, recent experimental evidence supports this notion. We simultaneously recorded field potentials from different cortical layers in primary visual cortex (area 17) and sensorimotor association cortex (area 7) in behaving cats. They were presented with two different visual stimuli and trained to respond by either watching one (no-go stimulus) or by pressing a lever seeing the other (go stimulus). We found that: (1) Compared to the no-go situation, the go stimulus induced a much stronger synchronization between the two areas. (2) Contrastingly, a highly salient but irrelevant stimulus failed to induce synchronized activity. (3) Furthermore, the increase in synchronization found between area 17 and area 7 was correlated with the correct performance of the task. (4) The synchronization pattern was layer specific and changed during the course of the task. Thus, the coupling between these two areas was dependent on the behavioral context. The synchronization pattern not only reflects Gestalt laws corresponding to bottom up synchronization, but can be influenced decisively by the internal state, corresponding to top down processing.