The magnitude of this spiking activity was still significantly lower than the respective magnitude of the discharge response when a preferred stimulus was perceptually dominant. However, the maintenance of a, higher than the sensory condition, firing rate during the suppression of a preferred stimulus could check details reflect an ongoing subliminal

process related to the nonconscious processing of a preferred visual pattern in the LPFC. Most likely, the effect we report here is not due to working memory, since we found that spiking activity is robustly suppressed when the preferred stimulus is not physically present. Rather, this result could be more related to a subliminal mechanism of nonconscious processing that coexists with the dominant mechanism of explicit, conscious processing in the LPFC and resembles the recently demonstrated activation of the inferior frontal cortex during the presentation of an unconscious no-go stimulus in human fMRI and electroencephalogram (EEG) studies (van Gaal et al., 2008 and van Gaal et al., 2010). It is likely that spontaneous fluctuations in such residual, subliminal activity might be tightly related to the

spontaneous perceptual alternations observed in BR. We also observed that high-frequency (>50 Hz) LFPs in the LPFC reflect click here subjective visual perception, while power in the beta frequency band (15–30 Hz) exhibited a tendency to decrease during the phenomenal perception of a preferred stimulus. Despite the fact that synchronous neural activity in the gamma frequency range has been suggested to mediate visual awareness (Crick and Koch, 1990), no evidence has been found until now for significant gamma modulation during conscious visual perception in the macaque cortex. Our findings suggest that this is most likely because LFPs have been studied in sensory cortices where perceptual modulation is generally weak but not in association cortices where neural activity appears to be more

correlated to phenomenal perception. second Indeed, both the power and interelectrode coherence of high-frequency oscillations in lower visual areas are not significantly modulated during perceptual suppression (Gail et al., 2004, Keliris et al., 2010, Maier et al., 2007 and Wilke et al., 2006; but see Fries et al., 1997 and Fries et al., 2002 for some opposite results in studies with strabismic cats). Thus, to our knowledge, our findings provide the first concrete indication that high-frequency oscillations reflect conscious perception in the macaque cortex. However, this correlate is not located in a primary sensory area such as V1 but in a higher association area such as the LPFC, in sites where spiking activity also reflects conscious perception. High-frequency oscillations in the gamma range have indeed been associated to conscious processing in a plethora of noninvasive human EEG and magnetoencephalography studies (for an extensive review, see Dehaene and Changeux, 2011).