Stanford Institute for Neuro-Innovation &
Translational Neuroscience
Consciousness has multiple components but philosophical, psychological, and physiological definitions remain works in progress. Laureys and coworkers have provided a useful graphical representaion of the more important components of consciousness, and of aberrant or pathological states of consciousness:
Awareness
(the content of consciousness) is positively
correlated to arousal, i.e. the level or degree of consciousness.
Normal human physiology exists along a continuum of this correlation
(red line), ranging from ~ 3,3 (x,y) to 9,9 (bounded by double lines),
also including a paradoxical dream state during REM sleep (~ 3,5 to
5,7). Pathological states (dashed lines) include a range
of conditions that often occur when awareness and arousal become
uncorrelated, or exist at the extremes of the correlation continuum
(i.e. < 4,4 or > 9,9). Anesthesia (single line) spans
a wide range of the correlation continuum and can be quantified using
loss of response metrics, such as loss of recall (6,6) and loss of
consciousness (L of C; 5,5) as well as other measures like EEG and
evoked potentials for
deep
levels of anesthesia, such as loss of response to surgical pain
(immobility; < 2.5,2.5). It
is possible to quantify some of
these conditions using Guedel's
classifications (I, II, III
to IV) or by using name
or face
recognition EEG, evoked potentials,
fMRI and neurological examination. Note
that some normal physiological, pathological and anesthetic states
appear to coexist along the continuum, such as: Deep Sleep, Coma, and Anesthesia, so there remain to be
discovered mechanistic
differences that discriminate these states at a more fundamental
level. An important goal of neuroscience is to characterize these
conscious states at the level of circuits of neurons, synapses and
molecules. Modified from Laureys
et al 2007
(Consiciousness and Cognition).