Gamma or no gamma, that is the question

Numerous studies suggest that gamma-band synchronization is central to visual processing, yet most of them have used artificial stimuli. A new study using electrocorticography (ECoG) in humans reported finding no gamma for many natural images and for visual noise. However, we highlight that sensitive metrics can reveal clear gamma not only for natural images, but for noise stimuli and even during the absence of visual stimuli. This shows the importance of using appropriate metrics for detecting rhythmic synchronization and investigating the function of gamma during natural viewing. Gamma-band synchronization has been related to several cognitive functions, in particular perceptual binding, selective attention, short- and long-term memory [1]. Many of these studies were performed in the visual domain using artificial stimuli, like drifting gratings. It is therefore crucial to investigate whether insights gained under controlled but artificial conditions also hold for natural conditions. As a first step, this requires testing whether gamma-band synchronization is at all present during natural viewing. We recently addressed this question by performing ECoG recordings from macaque monkeys as they freely viewed photographs of natural scenes [2]. Natural viewing led to pronounced gamma-band activity in visual cortex (Figure 1A, B), with a clear spectral peak indicative o