174 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”are the locus ceruleus (noradrenergic system) in the dorsal pons, and the
dorsal raphe nuclei (serotonin system) along the midline of the entire
brain stem (Table 8.2). Both are associated with behavioral vigilance.
The lateral hypothalamus is involved in the sleep-wake cycle. Its
destruction results in somnolence. This is due to a group of neurons
in this region that produces orexin, a small peptide capable of arousal.
Fibers from these neurons project to diverse places of the brain.23,24
In the aging human brain where the acetylcholine (ACh) activity is
low, pharmacologic stimulation of nicotinic acetylcholine receptor (nAChR)
is known to restore alertness and thus improve cognitive performance.
Mice with nAChR deleted genetically have impaired attention, and the
selective re-expression of the receptor in the brain corrects the deficit.^25
8.5 Impairment of Consciousness
8.5.1 Transient
Absent-mindedness (lack of focused attention) is common in normal
persons. Syncope (fainting) is a transient, benign condition resulting
from sudden drop of blood flow to the brain. It can be brought about
by postural change or by strong emotional states. Recovery is expected.
EEG during syncope is normal. Drowsiness, stupor, and coma are con-
ditions of decreasing alertness due to drug intake, metabolic disorder,
brain disease, or head trauma. EEG tracing usually simulates that of
slow-wave sleep. A person can either recover or die from coma within a
few days, or slip into one of the following permanent conditions.
8.5.2 Prolonged
Minimally conscious state is a condition in which a person is awake but
has only minimal awareness of the environment; interaction with people
is usually absent. EEG tracings may simulate that of drowsiness or sleep.
In the persistent vegetative state the patient has sleep/awake cycles but
is totally unaware of the environment. Some EEG activity is retained, as