Scientific Understanding of Consciousness
Consider some different states of consciousness
Normal, Wake-time Consciousness
For normal humans, wake-time consciousness includes both human-type consciousness and basal consciousness.
Dream State Consciousness
Consciousness could be defined to include the dreams of REM sleep.
If consciousness is defined to require some accumulation of memory, human infants would have a gradual transition to consciousness in the early postnatal time. Such definitions are likely to be contentious and not widely accepted.
Non-human Primate Consciousness
Non-human primates have basal consciousness and perhaps some aspects of human-type consciousness, depending on how consciousness is defined.
Consciousness could be defined to include basal consciousness for non-human animals, from non-human primates down to perhaps reptiles, but not insects, crustaceans, etc.
High Alert of Attention
Here is a report on one attempt to image brain activity during yoga. It should not be considered a professionally refereed report, such as those published in the journals Science and Nature.
Pictures of the brain's activity during Yoga Nidra
by Robert Nilsson — yogameditation.com
(Brain researcher Troels Kjær, The Kennedy Institute, Copenhagen, Denmark)
Researchers have for the first time succeeded in taking pictures of the brain during a meditative deep-relaxation, with as short an exposure time as one minute per photograph. The pictures were taken by one of the most advanced medical research instruments, the PET scanner at The State University Hospital in Copenhagen. The initiators were researchers, Dr. Hans Lou and Dr. Troels Kjær from the Kennedy Institute in Copenhagen.
It takes just one minute to gather the data of the brain scan, but there must also be an interval of ten minutes before the next picture can be taken. Eight pictures were produced from the scanned material. The pictures show which areas were active before (one picture), during (four pictures) and after Yoga Nidra (three pictures).
The person lying in the PET scanner is not disturbed by the photography, but practices the deep Yoga Nidra without a pause from start to finish.
At the same time the brain's activity was measured by an electroencephalograph (EEG) during the entire procedure. The EEG curve showed, as expected, that the subjects were in a meditative state during the entire Yoga Nidra.
Pictures were taken of a normal waking state with closed eyes, as well as pictures of four different practices in Yoga Nidra. By comparing this data and eliminating the normal activity from the activity during Yoga Nidra, it is possible to see in which areas of the brain the activity had increased during Yoga Nidra.
The measurements of the brain's activity (EEG) during Yoga Nidra indicated that the subjects were in a deeply relaxed state the whole time, similar to that of sleep. The theta activity rose significantly on all the twenty one electrodes (11%). The reduction of the alpha activity (2%) was insignificant; this shows that this meditative state is altogether different from that of the sleeping state and comprises conscious awareness. Furthermore, the state was constant and evenly distributed over the entire brain for the forty five minutes the relaxation lasted.
A rich body of observation supports the role of the cingulate cortex in most aspects of the hypnotic state. (Vogt; Cingulate Neurobiology, 385)
The hypnotic state is associated with an increase in rCBF in anterior cingulate and a reduction in posterior cingulate. (Vogt; Cingulate Neurobiology, 385)
The focused attention of the hypnotic state is hypothesized as a mechanism by which the activation of the various prefrontal circuits is decreased, eliminating their contribution to mediate conscious experience. (Vogt; Cingulate Neurobiology, 384)
Concussion, anesthesia, stroke, coma, etc.
Many abnormal states can result in impaired or no consciousness. Definitions would require many explicit details.
Vegetative states consciousness?
Extreme borders of consciousness might include some vegetative states?
Published in Volume 115, Issue 5 (May 2,2005)
Editorial: Raising consciousness
fMRI Research Center, Columbia University Medical Center, New York, New York, USA.
The national debate over Terri Schiavo exposed a critical gap between emotional fervor about brain-injured patients and the medical science that informs standards of care for them. Some of the questions raised in the public and legal forums point to a need for research and enhanced understanding of the mechanisms of recovery from disorders of consciousness.
In the aftermath of the stormy political, ethical, legal, familial, and medical controversies surrounding the sensationalized right-to-live versus right-to-die case of Terri Schiavo, we are left with heightened sensitivities to the plight of families and patients with disorders of consciousness. It is estimated that there may be as many as 15,000 patients in the United States who are in a persistent vegetative state (PVS) and more than 100,000 others who are in a minimally conscious state (MCS). Even though these cases present some of the most complicated medical and ethical issues of our time, families and physicians together often quietly weigh the options that surround these tragic circumstances and take appropriate actions without engagement of the entire United States government, politicians, the Supreme Court, state and local jurisdictions, clergy, protestors, special interest groups, and national and international media that emerged during the Schiavo case. Nonetheless, the frenzy that surrounded the case leaves some useful insights.
The differential diagnosis of PVS and MCS is based on the neurological examination. Patients in a PVS, like Terri Schiavo, demonstrate no signs of conscious behavior. They do, however, show spontaneous eye opening along with EEG evidence of sleep-wake cycles. These patients often do not require mechanical respiration or other life-support measures because dedicated brain stem circuits are able to sustain these functions. Further, the diagnostic criteria for PVS relies on the absence of behaviors that typically accompany conscious awareness such as sustained and reproducible, purposeful, or voluntary responses to sensory stimulation, language comprehension, or expression.
Patients in an MCS, on the other hand, retain limited and intermittent capacity for conscious behavior. These patients occasionally demonstrate clear-cut signs of self- or environmental awareness. In distinction to the diagnosis of PVS, the diagnosis of MCS is based on the presence of specific behavioral manifestations of conscious awareness. These behaviors occur inconsistently, must be differentiated reliably from reflexive, random, and spontaneous behavior, and include functions such as simple command following, production of yes/no responses, intelligible verbalization, and contingent behavioral responses such as appropriate affect, purposeful reaching, and pursuit eye movements. At present, there are no imaging procedures capable of distinguishing PVS and MCS conditions.