Article 5: A theoretically based index of conscious independent of sensory processing and behavior

Question 1

Perturbational complexity index (PCI)

Answer 1

This gauges the amount of information contained in the integrated response of the thalamocortical system to a direct perturbation.

• PCI value reflects the joint presence of integration and differentiation over a specific time window.
• It provides a value between 0 -1, representing the degree of complexity of information processing.

Question 2

Participants in article 5’s study

Answer 2

PCI was tested on a large data set of TMS evoked potentials recorded from healthy subjects during wakefulness, dreaming, non REM sleep, and different levels of sedation using anesthetic agents, as wel as from brain injured patients who had emerged from a coma.

Question 3

Results article 5

Answer 3

• Conscious and unconscious states differ from 100ms after TMS application (after the FFS).
• PCI discriminates level of consciousness in DOC.
• In patients with a stable clinical diagnosis of VS/UWS, PCI was as low as in healthy sleeping subjects and anesthetized subject, despite preserved levels of behavioral arousal.
• Conversely, PCI was as high in healthy awake subjects as in patients with LIS.
• PCI in patients with MCS tended to be lower than that of observed healthy awake subjects but was always above the highest value found in conditions in which consciousness was unambiguously lost (NREM sleep, anesthesia, VS).

Question 4

Advantages of method used in article 5

Answer 4

Does not depend on integrity of sensory pathway or on subjects ability to comprehend or carry out instructions. These experiments do not require any residual cognitive functions of the patients that might be absent whereas consciousness is still present.

Question 5

Recovery to consciousness (article 4)

Answer 5

1st pulse: administered the day the patient began to emerge from coma. Produced localized patterns that faded quickly.
2nd pulse: several days later, showed patterns that were more widespread and longer lasting.
3rd pulse: performed after the patients had regained consciousness, produced the most complex and longlasting patterns.

Immediately after TMS stimulation, PCI increased with similar rates in all consciousness states, values during wakefulness started to diverge from values during loss of consciousness about 100ms after stimulation.