Effect of illuminance and color temperature on lowering of physiological activity.
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To investigate how illuminance and color temperature in illumination affect the autonomic nervous system and central nervous system in conditions tending to lower physiological activity, and with an ordinary residential setting in mind, we performed an experiment on 8 healthy male subjects. The experimental conditions consisted of 4 conditions provided by a combination of 2 levels of color temperature (3000 K, 5000 K) and 2 levels of illuminance (30 lx, 150 lx). Physiological measurement was carried out during a process of 22 minutes of light exposure followed by 20 minutes of sleep in darkness. Heart rate variability (HRV) was used as an index of the autonomic nervous system, and alpha attenuation coefficient (AAC) and mean frequency of EEG were used as indices of the central nervous system. Subjective evaluation of drowsiness during the experiment was also carried out immediately following the 20 minutes sleep. No effect on HRV from illumination was noted, but significantly (p < 0.05) lower values for AAC were obtained under 3000 K conditions than 5000 K conditions in measurements during the first half of light exposure (Session 1). During alpha attenuation testing, significantly (p < 0.05) lower values for mean frequency in the theta-beta EEG bandwidth were also obtained under 3000 K conditions than 5000 K conditions, but that pattern persisted in measurement during the second half of light exposure (Session 2). Subjective drowsiness was also higher under 3000 K conditions than 5000 K conditions. These results suggest that low color temperature light creates a smooth lowering of central nervous system activity, and that low color temperature illumination can be used effectively in a bedroom or other such environment where it is desirable to facilitate lowered physiological activity. (+info)
Effect of wake-sleep transitions and rapid eye movement sleep on pharyngeal muscle response to negative pressure in humans.
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1. Genioglossus (GG) activation in response to upper airway negative pressure may be an important mechanism in the maintenance of airway patency. This reflex occurs during wakefulness but is diminished during stable non-rapid eye movement (NREM) sleep. Since obstructive events occur more commonly at wake-sleep transitions and during rapid eye movement (REM) sleep than during stable NREM sleep, we assessed the GG reflex during these two vulnerable states. 2. Seventeen healthy adults were studied throughout one evening and overnight. Electroencephalograms (EEGs), electro-oculograms (EOGs), submental electromyogram (EMG), GG EMG (intramuscular electrodes), and choanal plus epiglottic pressures were recorded. The GG reflex response to pulses of -8 cmH2O choanal pressure applied via nose mask during early inspiration was quantified repeatedly during relaxed wakefulness, within five breaths of wake-sleep transition (EEG alpha-theta transition) and during REM sleep. Only trials without EEG arousal were analysed, resulting in data from 14 subjects during sleep onset and 10 subjects during REM sleep (overall, 174-491 trials per state). 3. During wakefulness there was brisk GG reflex activation in response to negative pressure (amplitude: +78.5 +/- 28.3 % baseline (mean +/- s.e.m.); latency to maximal response: 177 +/- 16 ms). 4. At sleep onset, although there was marked variability among individuals, there was no significant reduction in the magnitude of the GG reflex for the group as a whole (amplitude: +33.2 +/- 8.2 % baseline; latency: 159 +/- 15 ms). 5. In contrast, during REM sleep there was a reduction of GG reflex (amplitude: -12.6 +/- 8.3 % baseline (P = 0.017 vs. awake); latency: 160 +/- 10 ms (n.s. vs. awake)) and greater airway collapsibility during the applied pressures (P = 0.043 vs. awake). 6. We conclude that there was no systematic reduction in the GG reflex to negative pressure at sleep onset. Nonetheless, it remains possible that sleep-deprived normal subjects and patients with sleep apnoea could react differently. 7. The apparent inhibition of the GG reflex during REM sleep may help explain why the upper airway is vulnerable to collapse during this state. (+info)
Investigation of nonlinear ECoG changes during spontaneous sleep state changes and cortical arousal in fetal sheep.
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We examined the processes of cortical activation and deactivation of the fetal brain during spontaneous sleep state transitions and during central nervous processing of vibroacoustic stimulations (VASs) using nonlinear analysis of the electrocorticogram (ECoG). Tests of nonlinearity and a random shuffling routine revealed deterministic and nonlinear portions in the fetal ECoG. As common nonlinear measures are not applicable to nonstationary time series, we developed an algorithm to estimate the predictability of the ECoG in its time course by means of a point prediction error (PPE). The ECoG was recorded before and during VAS from the maternal abdominal surface in seven chronically instrumented fetal sheep at 0.8 of gestation. The PPE during REM sleep was significantly higher than during NREM sleep. VAS in NREM sleep resulted in an abrupt increase of the PPE not reaching the level of REM sleep. The steep increase of the PPE at onset and its slow decrease after cessation of the stimulus were very similar to the dynamics of spontaneous sleep state transitions, suggesting the involvement of the same cortical activating mechanisms. In conclusion, the stage and the time course of fetal brain activation and deactivation patterns can be clearly shown by PPE techniques. The PPE is a useful complement to spectral analysis. Both techniques describe different properties of the ECoG. (+info)
Anticipatory biasing of visuospatial attention indexed by retinotopically specific alpha-band electroencephalography increases over occipital cortex.
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Alpha-band (8-14 Hz) oscillatory EEG activity was examined with high-density scalp electrical recording during the cue-stimulus interval of an endogenous spatial cueing paradigm. In different blocks, cued spatial locations (left or right) were in either the upper or lower visual field, and attended stimuli were either oriented Ts or moving dots. Distractor stimuli were equally likely in the uncued hemifield. Sustained focal increases of alpha-band activity were seen over occipital cortex contralateral to the direction of the to-be-ignored location (ipsilateral to the cued direction of attention) before onset of the to-be-attended stimulus. The focus of alpha-band activity also moved depending on whether cued locations were in the upper or lower field. Results are consistent with active gating of uncued spatial locations. (+info)
Oscillatory cortical activities in the gamma band in the human EEG induced by visual stimuli--representation of the stimulus?
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The present work presents three experiments investigating cortical activities in the gamma band in humans. On the basis of theoretical models and animal experiments, synchronized oscillatory neuronal activity is discussed as the key mechanism by which the brain binds information processesed in different cortical areas to form a percept. Using an identical stimulation design--the same as used in animal studies--it was shown that induced gamma band responses in the EEG resemble the same features as those found in the intracortical recordings of animals. In addition, the present work demonstrates that these cortical activities are not higher harmonics of the alpha band and that they are sensitive to the features of the stimulus. These results support the notion that gamma band activity is not just a by-product of neuronal activity and that alpha- and gamma band activities most certainly represent different cortical functional states. (+info)
Nonlinearity in human resting, eyes-closed EEG: an in-depth case study.
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The question of nonlinearity in the human electroencephalogram (EEG) is important, since linear methods of EEG analysis are more well-developed and computationally faster than nonlinear methods. Furthermore, the presence or absence of nonlinearity has important theoretical implications for understanding the nature of the brain's oscillatory activity. Using a linear summary measure as a control, we report a failure to reject the null hypothesis of a (largely) stationary linear-Gaussian process for normal, resting, eyes-closed EEG from a single participant. We found significant evidence of nonlinearity at two occipital sites (O1 and O2) where the 8-12.5 Hz alpha rhythm was prominent. However, this element of nonlinear structure appeared trivial, as (1) we found no evidence of time irreversibility at these loci, and (2) best-fitting linear models accounted on-average for over 94% of the variance in the data with nonlinear modeling doing no better. Half of the remaining variance could be accounted for by nonstationarity. While our findings technically apply only to the one individual tested, his EEG was typical of those seen under the conditions that we employed. (+info)
The role of the thalamic reticular neurons in alpha- and gamma-oscillations in neocortex: a mechanism for selective perception and stimulus binding.
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The long-term objective is to understand how large masses of neurons in the brain process information during various learning and memory paradigms. Both time- and space-dependent processes have been identified in animals through computer-based analytic quantifications of event-related extracellular potentials. New nonlinear analyses have been introduced that presume that the fine-grain variation in the signal is determined and patterned in phase-space. Some neurons in the primary visual cortex manifest gamma-band oscillations. These cells show both a nonspecific phase-alignment (response synchrony) and a specific tuning (orientation tuning) when stimuli are presented to their receptive fields. This dual regulation of the sensory cells is proposed to underlie stimulus binding, a theoretical mechanism for "object" perception. Nonlinear analytic results from gamma-activities in a simple model neuropil (olfactory bulb) suggest that neuroplasticity may arise through self-organization, a process in which a nonlinear change in the dynamics of the oscillatory field potentials is the hallmark. This self-organization may follow simple dynamical laws in which global cooperativity among the neurons is transiently brought about that, over trials, results in enduring changes in the nonlinear dynamics of some neurons. In conclusion, the sculpturing of the synaptic throughput in the sensory cortex (stimulus binding) may be associated with the irregular phases of the gamma-activities and may result from both specific and nonspecific systems operating together in a nonlinear self-organizing manner. (+info)
Neurophysiological measures of working memory and individual differences in cognitive ability and cognitive style.
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The capacity to deliberately control attention in order to hold and manipulate information in working memory is critical to higher cognitive functions. This suggests that between-subject differences in general cognitive ability might be related to observable differences in the activity of brain systems that support working memory and attention control. To test this notion, electroencephalograms were recorded from 80 healthy young adults during spatial working memory tasks. Measures of task-related neurophysiological and behavioral variables were derived from these data and compared to scores on a test battery commonly used to assess general cognitive ability (the WAIS-R). Subjects who scored high on the psychometric test also tended to respond faster in the experimental tasks without any loss of accuracy. The amplitude of the late positive component of the event-related potential was larger in high-ability subjects, and the frontal midline theta component of the EEG signal was also selectively enhanced in this group under conditions of sustained performance and high working memory load. These results suggest that subjects who scored high on the WAIS-R were better able to focus and sustain attention to task performance. Changes in the EEG alpha rhythm in response to manipulations of task practice and load were also examined and compared between frontal and parietal regions. The results indicated that high-ability subjects developed strategies that made relatively greater use of parietal regions, whereas low-ability subjects relied more exclusively on frontal regions. Other analyses indicated that hemispheric asymmetries in alpha band measures distinguish between individuals with relatively high verbal aptitude and those with relatively high nonverbal aptitude. In particular, subjects with a verbal cognitive style tended to make greater use of the left parietal region during task performance, and subjects with a nonverbal style tended to make greater use of the right parietal region. These results help clarify relationships between task-related brain activity and individual differences in cognitive ability and style. (+info)