| The neural correlates of perceptual awareness Summary Full Text |
| Alberto Capurro, Rodrigo Quian Quiroga |
| The study of the neural correlates of awareness is nowadays an active research field in Neuroscience. This has been basically boosted by the study of neural correlates of conscious perception with single cell recordings in monkeys and voxel activities with human fMRI experiments. In this review, we discuss the main experiments with recording of single neurons and related evidence about the neural events underling visual perceptual awareness.
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| Invisible is Better: Decrease of Subliminal Priming With Increasing Visibility Summary Full Text |
| Doris Eckstein, Dennis Norris, Matthew Davis, Richard Henson |
| Comparisons of indirect measures (e.g, subliminal priming) with direct measures (e.g, conscious reports, or prime discriminability) can help elucidate the relationship between nonconscious and conscious perception. We report three experiments on masked word priming in which we observed a negative correlation between prime discriminability (d’) and priming (RT), i.e. where priming decreased with increasing prime visibility. While such observations are rare (other empirical reports suggest instead a positive d’-priming relationship), they may indicate a conflict between conscious and nonconscious processing when primes are shown close to the subjective visibility threshold for the priming-relevant information. For instance, such a conflict could occur between nonconscious processing of a prime’s meaning and conscious perception of prime letters. Theoretical accounts that discuss similar conflicts assume that the conflict is resolved either by automatically prioritising conscious processes (Conscious Override Account) or by discounting the estimated confusion caused by a prime-target pair (Confusion Discounting Account). In both cases, priming is predicted to decrease when prime visibility increases from below threshold to perithreshold levels. Therefore, we suggest that negative priming-d’ relationships are most likely observed when the d’ measure assesses prime visibility at a level of representation that is below the level of representation at which priming arises, in terms of a putative hierarchy of word processing.
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| Brain Energy Supports the State of Consciousness Summary Full Text |
| Robert G. Shulman, Fahmeed Hyder, Douglas L. Rothman |
| Following the pragmatic practices of anesthesiologists an individual (human or animal) is defined to be in a state of consciousness empirically by the behavioral ability to respond to simple stimuli and the loss of consciousness is defined by the loss of that facility. Several brain activities are proposed as properties of the state of consciousness. Baseline brain energy consumption has been shown by 13C MRS to be almost completely used for neuronal signaling. PET measurements of glucose or oxygen consumption, from several laboratories, show a widespread ~45% reduction in cerebral energy during anesthesia-induced loss of consciousness. We propose that the high level of brain energy consumption of the awake state is a necessary property of the state of consciousness. Two additional neuronal properties are drastic changes in the patterns of fMRI activation and neuronal population activity at deep vs. light levels of anesthesia, which correspond to low vs. high energy states, respectively. The brain-wide fMRI activity patterns with rat sensory stimulation at the higher energy state (close to awake) collapses to contralateral somatosensory response at the lower energy state. Firing rates of an ensemble of neurons in the rat somatosensory cortex show that most of the energy in light anesthesia is consumed in the spiking frequency range of 20-40 Hz, which include γ-band electrical signals. In deep anesthesia the frequency range shifts to below 10 Hz. The high brain energy consumption, characteristic of the state of consciousness, supports elevated levels of high frequency neuronal firing observed in the resting, awake brain. In our model, necessary brain properties of the state of consciousness create our physical understanding of that state rather than the converse, popular in neuroimaging, in which subjective mental processes are identified to be necessary and sufficient correlates of the state of consciousness.
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| Conscious and unconscious processes in human desire Summary Full Text |
| Jackie Andrade, Jon May, David Kavanagh |
| Elaborated Intrusion theory (Kavanagh, Andrade & May, 2005) distinguishes between unconscious, associative processes as the precursors of desire, and controlled processes of cognitive elaboration that lead to conscious sensory images of the target of desire and associated affect. We argue that the latter play a key role in motivating human behaviour. Consciousness is functional in that it allows competing goals to be compared and evaluated. The role of effortful cognitive processes in desire helps to explain the different time courses of craving and physiological withdrawal.
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| Neurobiology of conscious and unconscious processes during waking and sleep Summary Full Text |
| Claude J. Gottesmann |
| Waking mind functioning comprises conscious and unconscious processes, with the latter being experimentally demonstrated by parapraxes and recent findings showing the active suppression of unwanted memories. According to psychoanalytic theory, these repression phenomena involve an unconscious censorship process. Today, neurobiological results show that this process seems to occur during waking rather than during the dreaming sleep stage.
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