The spectral exponent of the resting EEG indexes the presence of consciousness during unresponsiveness induced by propofol, xenon, and ketamine.

Despite the absence of responsiveness during anesthesia, conscious experience may persist. However, reliable, easily acquirable and interpretable neurophysiological markers of the presence of consciousness in unresponsive states are still missing. A promising marker is based on the decay-rate of the power spectral density (PSD) of the resting EEG.

Stratification of unresponsive patients by an independently validated index of brain complexity.

Objective: Validating objective, brain-based indices of consciousness in behaviorally unresponsive patients represents a challenge due to the impossibility of obtaining independent evidence through subjective reports. Here we address this problem by first validating a promising metric of consciousness-the Perturbational Complexity Index (PCI)-in a benchmark population who could confirm the presence or absence of consciousness through subjective reports, and then applying the same index to patients with disorders of consciousness (DOCs).

Methods: The benchmark population encompassed 150 healthy controls and communicative brain-injured subjects in various states of conscious wakefulness, disconnected consciousness, and unconsciousness.

Consciousness and Complexity during Unresponsiveness Induced by Propofol, Xenon, and Ketamine.

A common endpoint of general anesthetics is behavioral unresponsiveness, which is commonly associated with loss of consciousness. However, subjects can become disconnected from the environment while still having conscious experiences, as demonstrated by sleep states associated with dreaming. Among anesthetics, ketamine is remarkable in that it induces profound unresponsiveness, but subjects often report "ketamine dreams" upon emergence from anesthesia.

On the cerebral origin of EEG responses to TMS: insights from severe cortical lesions.

Background: Transcranial magnetic stimulation combined with electroencephalography (TMS/EEG) represents a valuable tool to probe cortical excitability and connectivity. Although several procedures have been devised to abolish TMS-related artifacts, direct evidence that it is possible to record TMS-evoked potentials (TEPs) that purely reflect cortical responses to TMS are still lacking.

Objective: To demonstrate that when TMS is delivered on a human head with intact nerves, scalp and ocular muscles, TEPs are present only if a functional portion of cortex is targeted and is absent otherwise.

Transcranial magnetic stimulation combined with high-density EEG in altered states of consciousness.

Background: This review discusses the advantages of transcranial magnetic stimulation combined with high-density electroencephalography (TMS-hdEEG) over other current techniques of brain imaging.

Methods And Results: Its application was reviewed, focusing particularly on disorders of consciousness, in the perspective of recent theories of consciousness. Assessment of non-communicative patients with disorders of consciousness remains a clinical challenge and objective measures of the level of consciousness are still needed.

Transcranial magnetic stimulation-evoked EEG/cortical potentials in physiological and pathological aging.

The frontal cortex undergoes macrostructural and microstructural changes across the lifespan. These changes can be entirely physiological, such as the ones occurring in elderly individuals who are cognitively intact, or pathological, such as the ones occurring in patients with Alzheimer's disease. Here, we use simultaneous electroencephalography (EEG) and transcranial magnetic stimulation (TMS) to study how the excitability of the frontal cortex changes during healthy and pathological aging.