A neurophysiological basis for aperiodic EEG and the background spectral trend.

Electroencephalograms (EEGs) display a mixture of rhythmic and broadband fluctuations, the latter manifesting as an apparent 1/f spectral trend. While network oscillations are known to generate rhythmic EEG, the neural basis of broadband EEG remains unexplained. Here, we use biophysical modelling to show that aperiodic neural activity can generate detectable scalp potentials and shape broadband EEG features, but that these aperiodic signals do not significantly perturb brain rhythm quantification.

Brain Responses to Propofol in Advance of Recovery from Coma and Disorders of Consciousness: A Preliminary Study.

Predicting recovery of consciousness in unresponsive, brain-injured individuals has crucial implications for clinical decision-making. Propofol induces distinctive brain network reconfiguration in the healthy brain as it loses consciousness. In patients with disorders of consciousness, the brain network's reconfiguration to propofol may reveal the patient's underlying capacity for consciousness.

Brain network motif topography may predict emergence from disorders of consciousness: a case series.

Neuroimaging methods have improved the accuracy of diagnosis in patients with disorders of consciousness (DOC), but novel, clinically translatable methods for prognosticating this population are still needed. In this case series, we explored the association between topographic and global brain network properties and prognosis in patients with DOC. We recorded high-density electroencephalograms in three patients with acute or chronic DOC, two of whom also underwent an anesthetic protocol.

Handgrip dynamometry for continuous assessment of volitional control during induction of anesthesia: a prospective observational study.

Purpose: Response to commands is the gold standard to assess the level of consciousness during anesthesia induction but it only provides an intermittent, binary measure with low temporal resolution. To overcome these limitations, we combined the object hold method with handgrip dynamometry to continuously record the force applied to hold a dynamometer as a surrogate measure of the level of consciousness during induction of anesthesia.

Methods: Fourteen patients scheduled for elective lumbar surgery and 14 age-matched non-anesthetized controls were enrolled.

Attenuation of High-Frequency (50-200 Hz) Thalamocortical Electroencephalographic Rhythms by Isoflurane in Rats Is More Pronounced for the Thalamus Than for the Cortex.

Background: Thalamocortical electroencephalographic rhythms in gamma (30-80 Hz) and high-gamma (80-200 Hz) ranges have been linked to arousal and conscious processes. We have recently shown that propofol causes a concentration-dependent attenuation of the power of thalamocortical rhythms in the 50 to 200 Hz range and that this effect is far more pronounced for the thalamus. To determine whether similar attenuation occurs with other anesthetics, we characterized the concentration-effect relationship of the inhaled anesthetic isoflurane on the spectral power of these rhythms.

Attenuation of high-frequency (50-200 Hz) thalamocortical EEG rhythms by propofol in rats is more pronounced for the thalamus than for the cortex.

Background: Thalamocortical EEG rhythms in gamma (30-80 Hz) and high-gamma (80-200 Hz) ranges have been linked to arousal and conscious processes. To test the hypothesis that general anesthetics attenuate these rhythms, we characterized the concentration-effect relationship of propofol on the spectral power of these rhythms. In view of the ongoing debate about cortex versus thalamus as the primary site of anesthetic action for unconsciousness, we also compared the relative sensitivity of cortex and thalamus to this effect propofol.

The sensory thalamus and cerebral motor cortex are affected concurrently during induction of anesthesia with propofol: a case series with intracranial electroencephalogram recordings.

Purpose: Brain imaging studies suggest that loss of consciousness induced by general anesthetics is associated with impairment of thalamic function. There is, however, limited information on the time course of these changes. We recently obtained intracranial electroencephalogram (EEG) recordings from the ventroposterolateral (VPL) nucleus of the thalamus and from the motor cortex during induction of anesthesia in three patients to study the time course of the alterations of cortical and thalamic function.

Attenuation of the 40-hertz auditory steady state response by propofol involves the cortical and subcortical generators.

Background: The 40-Hz auditory steady state response (40-Hz ASSR) provides a reliable marker of anesthetic-induced unconsciousness. Brain electric source analysis indicates that the 40-Hz ASSR arises from cortical and subcortical generators. The authors used source analysis to assess the effect of propofol anesthesia on the cerebral generators of the 40-Hz ASSR.

Preventing and managing pediatric obesity. Recommendations for family physicians.

Objective: To review the evidence on prevention and management of childhood obesity and to offer suggestions for family physicians.

Quality Of Evidence: Articles were obtained from a PubMed search. Most studies on pediatric obesity provide level II evidence.

Cortical processing of complex auditory stimuli during alterations of consciousness with the general anesthetic propofol.

Background: The extent to which complex auditory stimuli are processed and differentiated during general anesthesia is unknown. The authors used blood oxygenation level-dependent functional magnetic resonance imaging to examine the processing words (10 per period; compared with scrambled words) and nonspeech human vocal sounds (10 per period; compared with environmental sounds) during propofol anesthesia.

Methods: Seven healthy subjects were tested.

Influence of nociception and stress-induced antinociception on genetic variation in isoflurane anesthetic potency among mouse strains.

Background: Genetic background influences anesthetic potency to suppress motor response to noxious stimulation (minimum alveolar concentration [MAC]) as well as nociceptive sensitivity in unmedicated animals. However, the influence on MAC of baseline sensitivity to the noxious stimuli used to assess MAC has virtually never been studied. The authors assessed room air nociceptive sensitivity and isoflurane MAC in multiple mouse strains.

Brain imaging in research on anesthetic mechanisms: studies with propofol.

Brain imaging helps to refine our understanding of the anesthetic effect and is providing novel information that result in the formulation of hypotheses. They have shown that anesthetics act on specific structures that have been known to be important for consciousness at large. They have also helped to show that anesthetics act on specific structures regionally, rather than being non-specific, general depressant of the central nervous system (CNS).

Prolonged (more than ten hours) neuromuscular blockade after cardiac surgery: report of two cases.

Purpose: We examine two cases of prolonged neuromuscular blockade (NMB) after cardiac surgery. To the best of our knowledge, these are the first reported cases of complete paralysis lasting more than ten hours after surgery.

Clinical Features: We attribute the extended durations of NMB (more than ten hours) to high doses of NMB drugs in combination with magnesium sulphate and moderate renal failure.

Sparing of perceptual implicit memory despite suppression of the electrophysiological word repetition effect: a study with general anesthetic isoflurane.

Objective: Much effort has been devoted to the search for the neurophysiological correlates of implicit memory. A commonly held view is that the early portion (250-500 ms) of the event-related potential (ERP) word repetition effect reflects processes important for perceptual implicit memory whereas the latter portion reflects processes implicated in explicit memory. It is, however, difficult to disentangle with certainty the relative contributions of each form of memory on ERPs since both forms co-exist in normal subjects.

Autonomic nervous system response to epidural analgesia in laboring patients by wavelet transform of heart rate and blood pressure variability.

Background: Epidurals are effective in relieving labor pain but result in a sympathectomy that may compromise maternal hemodynamic stability and fetal perfusion. Decreases in blood pressure and heart rate can be corrected, but markers of autonomic activity would be useful to predict and prevent such changes. The goal of this study was to find markers describing the changes in autonomic nervous system activity with epidural anesthesia in laboring patients.

Dose-dependent effects of propofol on the central processing of thermal pain.

Background: Anatomic and physiologic data show that multiple regions of the forebrain are activated by pain. However, the effect of anesthetic level on nociceptive input to these regions is not well understood.

Methods: The authors used positron emission tomography to measure the effect of various concentrations of propofol on pain-evoked changes in regional cerebral blood flow.

PET quantification of muscarinic cholinergic receptors with [N-11C-methyl]-benztropine and application to studies of propofol-induced unconsciousness in healthy human volunteers.

This work evaluated kinetic analysis methods for estimation of the receptor availability of the muscarinic receptor using dynamic positron emission tomography (PET) studies with [N-(11)C-methyl]-benztropine. The study also investigated the effect of propofol on central muscarinic receptor availability during general anesthesia. Six volunteers were scanned three times, once for baseline while awake, once during unconsciousness, and once after recovery to conscious level.

Human auditory steady-state responses: the effects of recording technique and state of arousal.

Unlabelled: There is some controversy in the literature about whether auditory steady-state responses (ASSRs) can be reliably recorded in all subjects and whether these responses consistently decrease in amplitude during drowsiness. In 10 subjects, 40-Hz ASSRs became significantly different from background electroencephalogram activity with a probability of P < 0.01 and an average time of 22 s (range, 2-92 s), provided that the responses were analyzed with time-domain averaging rather than spectral averaging.