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Neuronal explosions and perceptual awarenessNeuronal explosions and perceptual awareness1.) Neuronal explosions: Neuronal dynamics underlying perceptual awareness in the cortex - Rafael Malach - non-linear changes in neuron activity related to conscious perception 2.) Theatre of the mind: Organisation of the human cortex during natural sensory stimulation - Rafael Malach - neural synchrony between sesnory and emotional brain regions 1.) Neuronal explosions: Neuronal dynamics underlying perceptual awareness in the cortex Rafael Malach, Weizmann Institute (2008) Keywords: neurons, neuronal explosions, consciousness, gamma synchrony A number of studies correlate high levels of fMRI signals with conscious perception. When either object images or facial images are presented for long enough to be at the border of perception, there is a highly non-linear increase in fMRI signals as between unconsciously and consciously detected signals. This occurs in the ventral stream object-recognition areas. Activity in this area correlates to the subjective experience of the perception rather than the physical character of the signal, seemingly in some way giving a functional role to subjectivity. Similar evidence emerges from studies of the well-known Rubin ambiguous vase-face illusion. High fMRI activity correlates with the emergence of a face perception, although this emergence into consciousness does not involve any alteration in the external signal (Hasson et al, 2001). This is another demonstration that brain activity can correlate to conscious perceptions rather than the nature of external signals. The authors consider that consciousness is correlated with non-linear increases in neural activity, here described as 'neuronal explosions' and occurring in sensory areas. Other fMRI studies have distinguished two types of fMRI reading. Sensory activity is marked by rapid but short bursts of neuronal firing, while rest activity in neurons involves slow, low amplitude activity. These conclusions look important for consciousness studies in a number of ways. Consciousness looks to be correlated to a rise in activity in particular neurons. This finding needs to be connected to rather similar experiments that show the global gamma synchrony as a strong correlate of consciousness, with global gamma associated with consciousness, while only local gamma arises when processing is unconscious. It seems possible that the synchrony provides some form of triggering for conscious activity in individual neurons. It is also stressed here that consciousness arises of its own accord in the sensory cortex, without being dependent on frontal cortices supposed to be related to the sense of self. This looks to undermine attempts to dismiss the problem of consciousness by conflating it with the self, and then after that deconstructing the self. On the other hand, it would probably be going too far in the other direction to say that consciousness does not arise at all in the frontal areas. In particular some activity in the orbitofrontal cortex can be correlated to conscious perception rather than the strength of the signal, in much the same way that Malach has indicated occurs with visual perceptions. 2.) Theatre of the mind: Organisation of the human cortex during natural sensory stimulation Rafael Malach, Weizmann Institute (2004) Keywords: sensory cortices, emotional brain, neural synchrony Malach et al attempted at a trial in which the brains of subjects were scanned while they watched a film that included emotional content. Malach pointed out that the use of a film contrasted with the more normal brain scanning procedure in which stationary objects are presented in isolation without being embedded in a background and without other modalities such as sound. With subjects watching a film there was synchronisation across 30% of the cortical surface. This synchronisation extended beyond both visual and auditory sensory cortices into association and limbic areas. Emotional scenes in the film were correlated with widespread cortical activation. The study appears interesting in terms of the ability to synchronise more than one sensory modality and the emotional areas of the brain. |
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