Mechanisms of Spatial Integration in Primary Visual Cortex of the Primate

Attention can selectively enhance neuronal responses and exclude external noise. To investigate these effects and their neuronal mechanisms we investigated spatial integration and the underlying neuronal mechanisms in primary visual cortex. We found evidence for spatial filtering mechanisms, whereby attention reduced spatial integration in macaque V I neurons. To study possible mechanisms of this effect, we measured length tuning in V I in the presence and absence of externally applied acetylcholine. The effects of acetylcholine application and attention in VI were largely similar. Acetylcholine reduced spatial integration by reducing the neuron's summation area. Thus, attention can alter perceptual and neuronal spatial integration, and acetylcholine may contribute to these task dependent receptive field dynamics.