Conscious content

I have been thinking about some information in a not too recent paper. (see citation below) Panagiotaropoulos and others looked at the location of the content of consciousness in primates. They used binocular flash suppression (BFS) to give two different visual stimulation that compete for a place in the content of consciousness. Here is their figure and description of the method:

We recorded simultaneously neuronal discharges and LFPs (local field potentials) in the LPFC (lateral prefrontal cortex) of two alert macaques during a passive fixation task that included randomly interleaved trials of physical alternation and BFS. BFS constitutes a highly controlled variant of BR (binocular rivalry) that has been extensively used to dissociate subjective visual perception from purely sensory stimulation. The BFS (‘‘perceptual’’) trials, as well as the physical (‘‘sensory’’) alternation of the visual stimuli that was used as a control condition, are depicted in Figure 1. Every trial starts with the presentation of a fixation spot in both eyes that is binocularly fused and remains on until the end of the trial. In both sensory (Figure 1A, upper panel, ‘‘Physical alternation’’) and perceptual (Figure 1A, lower panel, ‘‘Flash suppression’’) trials, a fixation spot was presented for 300 ms followed by monocular stimulation with the same visual pattern (a polar checkerboard in the paradigm presented in the figure). In perceptual trials, 1 s after stimulus onset, a disparate visual pattern (here, a monkey face) is suddenly flashed to the corresponding part of the contralateral eye. It has been repeatedly shown that, in both humans and monkeys, the flashed stimulus remains dominant for at least 1,000 ms, robustly suppressing the perception of the contralaterally presented visual pattern that is still physically present. … Thus, in perceptual trials, a visual competition period dissociating sensory stimulation from perception is externally induced for at least 1,000 ms. During this period, the newly presented image is perceptually dominant while the initially presented visual pattern is perceptually suppressed despite its physical presence in the retina (Figure 1A, middle panel). In sensory trials, the same visual patterns physically alternate between the two eyes, resulting in a visual percept identical to the perceptual condition but this time without any concurrent visual competition (Figure 1A, upper panel). Specifically, after 1 s of visual stimulation, the initially presented pattern is removed and immediately followed by the presentation of the disparate pattern in the contralateral eye.

Under this methodology it is possible to tell whether the neurons are registering the information that is actually on the retina or the information that is actually in consciousness, when they differ. Previous research has established that conscious content is not necessarily found in the visual system up to the completion of perception. The temporal lobe is the first place where the content of consciousness alone is registered in an area with a two-way communication with the lateral prefrontal cortex and that is why the researchers looked for the conscious signal in the LPFC (and we indeed found it). These two areas, as well as their direct connections, are each connected to a particular part of the thalamus, the pulvinar nucleus. This traffic seems to carry the mark of consciousness in the high frequency of the brain waves.

It is very interesting to see that the visual perception is complete and the ambiguities resolved for both the image that is conscious and the one that is unconscious before the temporal – prefrontal – thalamus signals show the content that is destined for awareness. There does not appear to be a difference between the processing of conscious and unconscious input up to the point of entering the consciousness loops. There are not two minds creating two perceptions, but one mind producing both perceptions, only one of which becomes conscious. The process of perception completes without, it appears, being affected by the mechanism of conscious awareness in any substantial way.

Here is the abstract:

Neuronal discharges in the primate temporal lobe, but not in the striate and extrastriate cortex, reliably reflect stimulus awareness. However, it is not clear whether visual consciousness should be uniquely localized in the temporal association cortex. Here we used binocular flash suppression to investigate whether visual awareness is also explicitly reflected in feature-selective neural activity of the macaque lateral prefrontal cortex (LPFC), a cortical area reciprocally connected to the temporal lobe. We show that neuronal discharges in the majority of single units and recording sites in the LPFC follow the phenomenal perception of a preferred stimulus. Furthermore, visual awareness is reliably reflected in the power modulation of high-frequency (>50Hz) local field potentials in sites where spiking activity is found to be perceptually modulated. Our results suggest that the activity of neuronal populations in at least two association cortical areas represents the content of conscious visual perception.

Panagiotaropoulos, T., Deco, G., Kapoor, V., & Logothetis, N. (2012). Neuronal Discharges and Gamma Oscillations Explicitly Reflect Visual Consciousness in the Lateral Prefrontal Cortex Neuron, 74 (5), 924-935 DOI: 10.1016/j.neuron.2012.04.013

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