This thesis examined changes in the brain's responses ("evoked potentials") during the transition from consciousness to unconsciousness. A negative wave, "N1", peaking at about 100 ms is affected by the subject's extent of attention/consciousness. Unfortunately, this same peak is also affected by manipulation of the physical parameters of the stimulus. The extent to which a component is affected by a physical or psychological parameter is often difficult to determine in the awake and alert subject. There are two principal reasons for this. Manipulation of the physical stimulus may inadvertently cause a change in the psychological state of the subject. Thus, subjects will attend to louder stimuli even if not asked to do so. Manipulation of the subject's level of attention also poses a dilemma. The change in the level of attention is always relative, not absolute. When subjects are asked to ignore stimuli, they are not able to do so. The sleep period provides a convenient means to resolve this dilemma. It is the period of time during which subjects are least attentive to, and thus least conscious of, their external environment. It can therefore be used to provide a baseline-near absolute level of attentiveness. Three experiments were run. In the first experiment, tones were presented to subjects at a rapid 600 ms interstimulus interval, during sleep onset (the transition period from Wakefulness through to Stage 2 of sleep). Subjects were not required to respond to the stimuli. In Experiment 2 stimuli were presented at a relatively slow rate (every 1000 msi. Again, subjects were not required to make an overt response. In Experiment 3 spatial resolution was enhanced by recording from 29 scalp electrode sites. Topographic changes to the P1-N1-P2 evoked potential complex during sleep onset were investigated. In addition, several novel methodological changes were implemented in this final study. Stimuli were presented in an oddball paradigm. Rare "target" tones were randomly presented within a train of frequently occurring standard stimuli. Subjects were required to press a hand held button whenever they detected a target stimulus. A radical interpretation of the present data is that a late negative wave, "N1", is entirely endogenous in nature. N1 may reflect the extent of the subject's conscious awareness of the external stimulus. As such, the N1 component of the auditory evoked potential provides a convenient and easy means to monitor the level of attention/consciousness in a number of applied settings. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/9717 |
| Date | January 1997 |
| Creators | de Lugt, Duncan R. |
| Contributors | Campbell, K. B., |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Detected Language | English |
| Type | Thesis |
| Format | 178 p. |
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