, 2009). An increase in the gamma power accompanied
by long-distance gamma synchrony was also observed in frontotemporal and parieto-occipital electrodes approximately 200 ms after the presentation of Raf inhibitor a Mooney face but not when the face was inverted and, thus, not recognized (Rodriguez et al., 1999). Interestingly, in the same study phase, desynchronization coexisted with above average gamma activity. In conclusion, our findings support the “frontal lobe hypothesis” of conscious visual perception (Crick and Koch, 1998), suggesting that the neural correlates of consciousness (NCC) should be related to explicit neural activity with direct access to planning stages of the brain, like the prefrontal cortex. In fact, our results demonstrate that the NCC are embedded in the LPFC, a cortical area having direct connections to premotor and motor cortices, thus with direct access to motor output. However, the fact that neural activity in two cortical areas (LPFC and temporal cortex) reflects phenomenal perception in an all-or-none manner supports the view that consciousness is not localized in a unique cortical area but, rather, is an emergent property of global networks
of neuronal populations (Blake and Logothetis, 2002). The cranial headpost, scleral eye coil, and recording chamber were implanted in two monkeys under general anesthesia Y-27632 molecular weight using aseptic and sterile conditions. The recording isothipendyl chamber (18 mm in diameter) was centered stereotaxically above the LPFC (centered toward the inferior convexity of the LPFC, defined as the area anterior to the arcuate and ventral to the principal sulcus) based on high-resolution MR anatomical images collected in a vertical 4.7 T scanner with a 40-cm-diameter bore (Biospec 47/40c; Bruker Medical, Ettlingen, Germany). We used custom-made
tetrodes made from Nichrome wire and electroplated with gold to decrease the impedances below 1 MΩ. We recorded LFP signals by filtering the raw voltage signal using analog band bass filtering (high-pass set at 1 Hz and low-pass at 475 Hz) and digitized at 2 kHz (12 bits). MUA was defined as the events detected in the high-pass analog filtered signal (0.6–6 kHz) that exceeded a predefined threshold (typically, 25μV) on any tetrode channel. The 0.6–6 kHz recorded signal was sampled at 32 kHz and digitized at 32 kHz (12 bits). The recorded signals were stored using the Cheetah data acquisition system (Neuralynx, Tucson, AZ, USA). We identified single units by employing a spike-sorting method using the first three principal components of the recorded waveforms as features (a method previously described in Tolias et al., 2007). Eye movements were monitored online and stored for offline analysis using the QNX-based acquisition system (QNX Software Systems Ltd.) and Neuralynx.
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