Attention Modulates Gamma-band Oscillations Differently in the Human Lateral Occipital Cortex and Fusiform Gyrus

Abstract

We studied the existence, localization and attentional modulation of gamma-band oscillatory activity (30-130 Hz) in the human intracranial region. Two areas known to play a key role in visual object processing: the lateral occipital (LO) cortex and the fusiform gyrus. These areas consistently displayed large gamma oscillations during visual stimulus encoding, while other extrastriate areas remained systematically silent, across 14 patients and 291 recording sites scattered throughout extrastriate visual cortex. The lateral extent of the responsive regions was small, in the range of 5 mm. Induced gamma oscillations and evoked potentials were not systematically co-localized. LO and the fusiform gyrus displayed markedly different patterns of attentional modulation. In the fusiform gyrus, attention enhanced stimulus-driven gamma oscillations. In LO, attention increased the baseline level of gamma oscillations during the expectation period preceding the stimulus. Subsequent gamma oscillations produced by attended stimuli were smaller than those produced by unattended, irrelevant stimuli. Attentional modulations of gamma oscillations in LO and the fusiform gyrus were thus very different, both in their time-course (preparatory period and/or stimulus processing) and direction of modulation (increase or decrease). Our results thus suggest that the functional role of gamma oscillations depends on the area in which they occur.

Neural Dissociation between Visual Awareness and Spatial Attention

“…Oscillatory activity in the gamma range has been functionally related, in separate studies, to conscious perception Fries et al, 2002;Schurger et al, 2006;Wilke et al, 2006) as well as attentional selection (Gruber et al, 1999;Tallon-Baudry et al, 2005;Landau et al, 2007;Womelsdorf and Fries, 2007). Our results thus confirm the involvement of gamma-band activity in both visual awareness and spatial attention.…”

“…However, the results further show that distinct frequency components of the gamma-band response may support flexibly and simultaneously distinct cognitive functions (Vidal et al, 2006;Buschman and Miller, 2007). Such a frequency specialization suggests that gamma-band synchronization is not a monolithic mechanism in charge of a single cognitive function (Tallon-Baudry, 2004;Tallon-Baudry et al, 2005;Buzsaki, 2006). In the present study, the modulation of the high-frequency gamma-band activity could reflect the selective neural amplification of attended signals in the visual cortex (Reynolds and Chelazzi, 2004), whereas the mid-frequency gamma-band activity could reflect the reverberation process that characterizes perceptual awareness per se according to current views (Tononi and Edelman, 1998;Dehaene et al, 2006;Lamme, 2006;Buzsaki, 2007).…”

Parieto-frontal gamma band activity during the perceptual emergence of speech forms

“…Recent iEEG studies have put a strong emphasis on gamma band activations in particular, in association with a wide range of cognitive processes, including memory (Fell et al, 2001;Howard et al, 2003;Mainy et al, 2007), visual attention and perception (Brovelli et al, 2005;Lachaux et al, 2000Lachaux et al, , 2005Tallon-Baudry et al, 2005;Tanji et al, 2005), audition (Bidet-Caulet et al, 2003;Edwards et al, 2005), somatosensory and motor processes Crone, Sinai and Korzeniewska, 2006;Lachaux et al, 2005;Aoki et al, 1999;Pfurtscheller et al, 2003;Szurhaj et al, 2005), and language . Importantly, in all those studies, gamma band activity was observed only in very specific brain regions, dependant on the tasks, and in good agreement with the functional networks revealed by fMRI .…”

Different Effects of Voluntary and Involuntary Attention on EEG Activity in the Gamma Band

“…In initial studies gamma activity was measured to stimuli requiring perceptual integration to form a visible object. However, because the object requiring binding was also the object of attention, it was unclear whether the factor eliciting the increases in induced gamma in these studies was perceptual binding, attentional selection or some combination of the two (Tallon-Baudry et al, 2005).…”