Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

170 Self and the Phenomenon of Life

b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”

deep brain structures, in particular the thalamus. EEG is sensitive in
detecting seizure activity in the brain, even when a person is not actively
in convulsion. Recent progress consists of direct recording on the
exposed brain. The method becomes even more powerful when multiple
electrodes are simultaneously applied. The limitation to this approach is
that the procedure is invasive and needs justification when carried out on
people. For this reason, direct recording on the human brain is confined
to patients undergoing brain surgery.
A variant of EEG is magneto-encephalogram (MEG), which
records variations in magnetic properties; it is superior for detecting
deep brain activities but has less resolution power. A combination of
EEG, MEG and functional MRI (magnetic resonance imaging) provides
more information than any one alone.

8.4 Neurology of Consciousness

The neurophysiologic mechanisms of consciousness can be divided into
two categories: those for specific sensations and perceptions (discrete
mode); and those for general arousal (diffuse mode). See Table 8.2.

Table 8.2. Brain Structures Relevant to Consciousness

A. Discrete Consciousness (content relevant) —
Inputs from spinal tracts and cranial nerves project to discrete brain sensory areas such
as the somatosensory, visual, and auditory cortices, following a relay in the thalamus.

B. Diffuse Consciousness (content irrelevant; general alertness) —
There are four components:

(1) Brain stem reticular activating system: Sends short fibers to thalamus which then
projects to diverged cerebral cortical areas.
(2) Locus ceruleus (in dorsal pons): Sends noradrenergic-producing fibers to diverged
areas including cerebral cortex, cerebellar cortex, olfactory bulb (in rats), thalamus,
and hypothalamus.
(3) Dorsal raphe nuclei (spread out along brainstem): Sends serotonin-producing
fibers to thalamus, cerebral cortex, cerebellar cortex, and neostriatum (caudate and
putamen).
(4) Lateral hypothalamus: Sends orexin-producing fibers to posterior hypothalamus,
thalamus, locus ceruleus, dorsal raphe nuclei, and the frontal lobe.