In the last decade, the brain\'s oscillatory responses have invaded the literature. The studies on delta (0.5-3.5Hz) oscillatory responses in humans upon application of cognitive paradigms showed that delta oscillations are related to cognitive processes, mainly in decision making and attentional processes. The present manuscript comprehensively reviews the studies on delta oscillatory responses upon cognitive stimulation in healthy subjects and in different pathologies, namely Alzheimer\'s disease, Mild Cognitive Impairment (MCI), bipolar disorder, schizophrenia and alcoholism. Further delta oscillatory response upon presentation of faces, facial expressions, and affective pictures are reviewed. The relationship between pre-stimulus delta activity and post-stimulus evoked and event-related responses and/or oscillations is discussed. Cross-frequency couplings of delta oscillations with higher frequency windows are also included in the review. The conclusion of this review includes several important remarks, including that delta oscillatory responses are involved in cognitive and emotional processes. A decrease of delta oscillatory responses could be a general electrophysiological marker for cognitive dysfunction (Alzheimer\'s disease, MCI, bipolar disorder, schizophrenia and alcoholism). The pre-stimulus activity (phase or amplitude changes in delta activity) has an effect on post-stimulus EEG responses.

The organophosphorus (OP) compound soman is known to produce long-lasting epileptic seizure activity and associated brain damage. The present paper reviews the findings of five recent studies that tentatively established correlations between the development of soman-induced neuropathology and some subtle changes in the electrocortigraphic (ECoG) power spectrum. It is important to note that the reported experiments have been performed independently by three different teams (France, The Netherlands, USA) in various animal models (rat, guinea-pig, cynomolgus monkey) through different protocols of intoxication, pharmacological environments, and methods for ECoG spectral analysis. Despite these disparities, the five studies show that a suistained shift of ECoG power toward the lowest frequency range, i.e. the delta band, occurs within the first hours of soman-induced seizures. This early ECoG spectral change is concurrent with the first neuropathological changes in brain and is almost constantly followed, days or weeks later, by at least minimal neuropathology. Moreover the relative contribution of delta activity to the ECoG power spectrum still remains abnormally high for 1-3 days after seizure onset, i.e. within the phase of damage maturation. On the other hand, somnan-induced neuropathology was not observed in non-seizuring animals in which the delta activity was not increased above the pre-soman baseline. Similarly, no brain damage was ever shown in seizuring subjects in which the initial delta change eventually normalized after the curative administration of efficient anticonvulsant drugs such as the non-competitive antagonists of the NMDA receptor. These results, in agreement with previously published observations, strongly suggest that an increase of the relative power in the delta band might be a real-time marker of the ongoing development of soman-induced, seizure-related cerebral lesions and a reliable predictor for the final neuronal losses to come. Therefore, the monitoring of delta activity during the 24-72 h period that follows soman exposure may potentially be a useful tool to follow \"on-line\" the progression of brain damage and to control the neuroprotective activity of\'a medication. Moreover since the method is non-invasive in man and since the above-presented results have been partly found in primates, the applicability of spectral analysis as a prognostic means in human OP poisoning ought to be seriously considered.

Driver fatigue is a major cause of road accidents and has implications for road safety. This review discusses the concepts of fatigue and provides a summary on psychophysiological associations with driver fatigue. A variety of psychophysiological parameters have been used in previous research as indicators of fatigue, with electroencephalography perhaps being the most promising. Most research found changes in theta and delta activity to be strongly linked to transition to fatigue. Therefore, monitoring electroencephalography during driver fatigue may be a promising variable for use in fatigue countermeasure devices. The review also identified anxiety and mood states as factors that may possibly affect driver fatigue. Furthermore, personality and temperament may also influence fatigue. Given the above, understanding the psychology of fatigue may lead to better fatigue management. The findings from this review are discussed in the light of directions for future studies and for the development of fatigue countermeasures.

Since the turn of the century, it has been postulated that humoral factors induce sleep. Many compounds were proposed as sleep-factors, but only two of the sleep-peptides have been purified to homogeneity and characterized, so far. One of them, DSIP, was shown to be a nonapeptide of MW 849 and to induce mainly delta-sleep in rabbits, rats, mice, and humans, whereas in cats, the effect on REM sleep was more pronounced. A U-shaped activity curve was determined for the dose as well as for the time of infusion. DSIP-like material was found by RIA and immunohistochemistry in brain and by RIA in peripheral organs of the rat as well as in plasma of several mammals. In addition to sleep, the peptide also has been observed to affect electrophysiological activity, neurotransmitter levels in the brain, circadian and locomotor patterns, hormonal levels, psychological performance, and the activity of neuropharmacological drugs including their withdrawal.

The present paper combines a review of event-related potentials (ERPs) with empirical data concerning the question: what are the differences between auditory evoked potentials (EPs) and two types of ERPs with respect to their frequency components? In this study auditory EPs were elicited by 1500 Hz tones. The first type of ERPs was responses to 3rd attended tones in an omitted stimulus paradigm where every 4th stimulus was omitted. The second type of ERPs was responses to rare 1600 Hz tones in an oddball paradigm. The amplitudes of delta and theta components of EPs and ERPs showed significant differences: in responses to 3rd attended tones there was a significant increase in the theta frequency band (frontal and parietal locations; 0-250 ms). In the delta frequency band there was no significant change. In contrast a diffuse delta increase occurred in oddball responses and an additional prolongation of theta oscillations was observed (late theta response: 250-500 ms). These results are discussed in the context of ERPs as induced rhythmicities. The intracranial sources of ERPs, their psychological correlates and the role of theta rhythms in the cortico-hippocampal interaction are reviewed. From these results and from the literature a working hypothesis is derived assuming that delta responses are mainly involved in signal matching, decision making and surprise, whereas theta responses are more related to focused attention and signal detection.