A measure combining fractal dimensions of brain activity—capturing both integration and differentiation of cortical responses—can distinguish conscious from unconscious states almost perfectly within individuals. In 18 healthy subjects, the Fractal Dimension Index (FDI) derived from high-density EEG after transcranial magnetic stimulation was significantly lower during non-REM sleep and sedation (with xenon or propofol) than during wakefulness. The index reflects how complex and differentiated the brain's spatiotemporal responses are to a perturbation. The findings suggest that tracking fractal dimensions of cortical dynamics offers a way to assess consciousness, with potential clinical applications for detecting awareness in patients.
Meditation involves complex emotional and attentional training that may improve self-awareness, emotion regulation, attention, and brain structure, but its neurophysiology is not well understood. Transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) offers a non-invasive way to probe brain activity and connectivity. This work aims to determine whether TMS-EEG can detect changes in brain reactivity during meditation and whether those changes are specific to the meditative state and the brain region stimulated.
A general principle for sizing up consciousness, grounded in information integration theory (IIT), is explored. The book addresses why the brain but not other organs hosts experience, why consciousness fades in deep sleep yet returns in dreams, and whether unresponsive patients, parrots, octopuses, or computers can be conscious. Theoretical principles are translated into anatomical observations and novel empirical measurements, including an index of brain complexity applicable at the bedside of brain-injured patients. The authors aim to describe a preliminary attempt to identify a general rule for assessing the capacity for consciousness within and beyond the human skull.