December 30, 2006

Visuo-spatial consciousness and parieto-occipital EEGs

Which brain areas are involved in visuospatial consciousness? In a recent study by Babiloni and colleagues, subjects performed a visual perception task. Interestingly, these scientists found that visual-evoked potentials at parieto-occipital areas had the same peak latencies for cases of conscious, as well as unconscious, perception. These visual-evoked potentials were located to the occipital (BA 19) and parietal (BA 7) cortices.

Source strength was significantly stronger in consciously, compared to unconsciously, perceived cases at about +300 ms poststimulus. Babiloni and colleagues concluded that these features of the observed parieto-occipital activation might be connected to visuospatial consciousness.

In the study described above, Babiloni and colleagues used electroencephalograms (EEGs) to study brain activations correlated with visuo-spatial processes. EEGs are recordings of “brain waves”. In more complicated terms, EEGs are electrical potentials that are recorded by placing electrodes on the scalp or in the brain. To record EEGs, at least two electrodes are needed. This is because the EEG is a measurement of the difference in the electrical potentials detected by the electrodes. Typically, one electrode is attached to the scalp to measure the electrical activity of neurons in the underlying brain area, while a second electrode is attached to the ear lobe, where there is not any electrical activity to measure. The electrical fluctuations in the brain are rather small (often much less than a millivolt), however, they can be amplified and displayed on an oscilloscope and then transferred to paper on a chart recorder. Scientists have found these recordings helpful for 1) diagnosing epilepsy and brain damage, 2) studying sleep and normal brain function, and 3) monitoring anesthesia.

Visuo-spatial consciousness and parieto-occipital areas: a high-resolution EEG study.
Babiloni C, Vecchio F, Miriello M, Romani GL, Rossini PM.
Cereb Cortex. 2006 Jan;16(1):37-46.

Conscious and unconscious visuo-spatial processes are mainly related to parieto-occipital cortical activation. In this study, the working hypothesis was that a specific pattern of parieto-occipital activation is induced by conscious, as opposed to unconscious, visuo-spatial processes. Electroencephalographic data (128 channels) were recorded in 12 normal adults during a visuo-spatial task. A cue stimulus appeared on the right or the left (equal probability) monitor side for a ‘threshold time’ inducing approximately 50% of correct recognitions. It was followed (after 2 s) by visual go stimuli at spatially congruent or incongruent positions with reference to the cue location. The left (right) mouse button was clicked if the go stimulus appeared on the left (right) monitor side. Subjects were required to say ‘seen’ if they had detected the cue stimulus or ‘not seen’ if they missed it (self-report). ‘Seen’ and ‘not seen’ electroencephalographic trials were averaged separately to form visual evoked potentials. Sources of these potentials were estimated by LORETA software. Reaction time to go stimuli was shorter during spatially congruent than incongruent ‘seen’ trials, possibly due to covert attention on cue for self-report. It was also shorter during spatially congruent than incongruent ‘not seen’ trials, as an objective sign of unconscious processes. Cue stimulus evoked parieto-occipital potentials which has the same peak latencies in the ‘seen’ and ‘not seen’ cases. Sources of these potentials were located in occipital area 19 and parietal area 7. Source strength was significantly stronger in ‘seen’ than ‘not seen’ cases at approximately +300 ms post-stimulus. These results may unveil features of parieto-occipital activation accompanying visuo-spatial consciousness.

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