Consciousness is the experience of monitor images in the mind. At any moment,
you are and the world are revealed in your own separate consciousness.
Everything that exists is manifest in consciousness.
Paradoxically, we also know that much, if not most, brain activity occurs
without the benefit of consciousness. Psychoanalytic and other metaphysical
descriptions of the mind invented the “unconscious” or the “subconscious” to try
to explain some of the more peculiar aspects of human behavior. Often
consciousness and the subconscious were set apart as adversaries in a
subterranean battle of mind. Modern neuroscience would suggest that all brain
activity carries on below the surface and only a glimmer of this continuous
brain processing is projected into consciousness as a monitor image.
The study of
the brain has not revealed exactly how consciousness is produced but we know
some important and practical things about consciousness. If we thought in terms
of a consciousness module in the brain, we could assume that the module might
have high-level executive functions and at the same time creates a monitor
image. The deep question is that if I am that consciousness that is the monitor
image of my brain activity, where exactly do I exist?
As a monitor
image of brain activity, consciousness will support different content. The
contents of consciousness vary continuously and mostly involuntarily. We can
refer to the contents of consciousness as "awareness" and you are more aware
when the contents of consciousness are rich and varied. The underlying process
of consciousness involves bringing monitor images of the outside world together
with monitor images of inside the body. Images of the outside tend to be
detailed and explicit in consciousness.
When you can
see, a marvelously detailed and interesting moving picture of what is out there
dominates consciousness. The information content of the picture is enormous. If
you try to record all the visual information in a few seconds of visual scanning
your environment, you would consume gigabytes of computer memory. Thus
consciousness consists of realtime monitor images that are not recorded in
Neurophysiology of Consciousness
Consciousness depends on spontaneously emitted pulses from brain stem
neurons that ascend in a complex mesh of activating circuits to awaken
neurons in the limbic system, thalamus, and cerebral cortex. Without
this ascending activation, humans lapse into a coma. Four
neurotransmitters appear to be most important in creating consciousness:
norepinephrine, serotonin, dopamine and acetylcholine. Drugs such as
anesthetics that interrupt consciousness interfere with cortical
In my imagination, I visualize a fountain-like activity in the brain
that produces consciousness. The base of the fountain is the brain stem
that sends an upward stream of activity into a lens-like structure, the
thalamus that disperses the stream into all areas of the brain. The
fountain stream returns to the thalamus and the cycle begins again with
the brain stem acting as the pump.
Pacemaking neurons in the brainstem fire rhythmically, sending
activating pulses upwards into the thalamus. Pulses of electrical
activation are accompanied by pulses of chemicals released to tonically
activate regions of the brain. The thalamus, in turn, activates the
cerebral cortex and links all subsystems in meaningful packages of
activity that deliver monitor images of their activity to consciousness.
Cortical neurons return signals to the thalamus so that cortical
activation can be regarded as a looping system that recurs and
No one knows what part of the brain produces the conscious monitor
images. Likely, the images depend on the recursive interaction of the
thalamus and cortex. Other modulating information is fed into the mix
from the smaller nuclei surrounding the thalamus contributing feelings,
mood and other information. Later I will develop the idea that the
thalamus is the multi-channel mixer in the brain that combines activity
from many brain modules using function-specific templates. The templates
are base on innate patterns and are modified by learning.
The consciousness system sustains a sense of continuity and stability
that can be interrupted abruptly by a novel signal from the outside or
inside the body. Strong emotions, such as anger and fear are action
templates stored in the amygdala that quickly change the entire
consciousness mix. Emotions interrupt other activities and “take over”
consciousness, sending a volley of signals to many destinations in the
body and brain.
In their review of 10 years of studying the connections of thalamic
nuclei in rats, Van der Werf et al stated: ”The thalamic midline and
intralaminar nuclei, long thought to be a non-specific arousing system
in the brain, have been shown to be involved in separate and specific
brain functions, such as specific cognitive, sensory and motor
functions. Fundamental to the participation of the midline and
intralaminar nuclei in such diverse functions seems to be a role in
They proposed that the midline and intralaminar nuclei mediate
awareness. Each of the groups have a distinct role in a different aspect
(1) a dorsal group, consisting of the paraventricular, parataenial
and intermediodorsal nuclei, involved in viscero-limbic functions
(2) a lateral group, comprising the central lateral and paracentral
nuclei and the anterior part of the central medial nucleus, involved in
(3) a ventral group, made up of the reuniens and rhomboid nucleus and
the posterior part of the central medial nucleus, involved in multimodal
4) a posterior group, consisting of the centre median and
parafascicular nuclei, involved in limbic motor functions.
Because the thalamus is so complexly interconnected with all other
parts of the brain, a thalamic model of executive function will be
misleading to some extent. A combination of frontal lobe and thalamic
circuits is essential, for example, for anticipatory planning,n
one of the more recent and complex attributes of cognition.
Philosophers declared that consciousness is a fundamental property of the
universe equivalent to gravity and electromagnetic radiation. In their
view, consciousness enters and leaves an animal or human body and is
neither created nor destroyed. I like the idea and wish it were true. I cannot
imagine a way to refute the idea of consciousness as an independent force in the
universe. There is no need to refute the idea.
Consciousness cannot be constrained by definition, cannot be captured by description, and cannot be
limited by measurement.