Page 349 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

Consciousness, Memory, Language pocampus, perirhinal, entorhinal and parahip-
pocampal cortex, etc.). It establishes the tem-
Consciousness. Selective attention, abstract poral and spatial context surrounding an ex-
thinking, the ability to verbalize experiences, perience and recurrently stores the informa-
the capacity to plan activities based on ex- tion back into the spines of cortical dendrites in
perience, self-awareness and the concept of the association areas (! p. 322). The recur-
values are some of the many characteristics of rence of a portion of the experience then suf-
fices to recall the contents of the memory.
consciousness. Consciousness enables us to
Central Nervous System and Senses activity associated with consciousness and automatically for less than 1 s. A small fraction
Explicit learning (! A) starts in the sensory
deal with difficult environmental conditions
(adaptation). Little is known about the brain
memory, which holds the sensory impression
controlled attention (LCCS, see below), but we
of the information reaches the primary
do know that subcortical activation systems
memory (short-term memory), which can re-
tain about 7 units of information (e.g., groups
such as the reticular formation (! p. 322) and
corticostriatal systems that inhibit the afferent
of numbers) for a few seconds. In most cases,
signals to the cortex in the thalamus (! p. 326)
the information is also verbalized. Long-term
storage of information in the secondary
play an important role.
memory (long-term memory) is achieved by
Attention. Sensory stimuli arriving in the
sensory memory are evaluated and compared
to the contents of the long-term memory
is the place where frequently repeated impres-
within fractions of a second (! A). In routine
sions are stored (e.g., reading, writing, one’s
own name); these things are never forgotten,
12 situations such as driving in traffic, these repetition (consolidation). The tertiary memory
stimuli are unconsciously processed (auto-
and can be quickly recalled throughout one’s
mated attention) and do not interfere with lifetime. Impulses circulating in neuronal tracts
other reaction sequences such as conversation are presumed to be the physiological correla-
with a passenger. Our conscious, selective (con- tive for short-term (primary) memory,
trolled) attention is stimulated by novel or am- whereas biochemical mechanisms are mainly
biguous stimuli, the reaction to which (e.g., the responsible for long-term memory. Learning
setting of priorities) is controlled by vast parts leads to long-term genomic changes. In addi-
of the brain called the limited capacity control tion, frequently repeated stimulation can lead
system (LCCS). Since our capacity for selective to long-term potentiation (LTP) of synaptic con-
attention is limited, it normally is utilized only nections that lasts for several hours to several
in stress situations. days. The spines of dendrites in the cortex play
The implicit memory (procedural memory) an important role in LTP.
stores skill-related information and informa- Mechanisms for LTP. Once receptors for AMPA
tion necessary for associative learning (condi- (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic
tioning of conditional reflexes; ! p. 236) and acid) are activated by the presynaptic release of glu-
+
non-associative learning (habituation and tamate (! p. 55 F), influxing Na depolarizes the
sensitization of reflex pathways). This type of postsynaptic membrane. Receptors for NMDA (N-
methyl-D-aspartic acid) are also activated, but the
unconscious memory involves the basal gan- Ca channels of the NMDA receptors are blocked by
2+
glia, cerebellum, motor cortex, amygdaloid Mg , thereby inhibiting the influx of Ca 2+ until the
2+
body (emotional reactions) and other struc- Mg 2+ block is relieved by depolarization. The cyto-
2+
2+
tures of the brain. solic Ca concentration [Ca ] i then rises. If this is re-
The explicit memory (declarative/knowl- peated often enough, calmodulin mediates the auto-
edge memory) stores facts (semantic knowl- phosphorylation of CaM kinase II (! p. 36), which
2+
edge) and experiences (episodic knowledge, persists even after the [Ca ] i falls back to normal.
CaM kinase II phosphorylates AMPA receptors (in-
especially when experienced by selective at- creases their conductivity) and promotes their inser-
tention) and consciously renders the data. tion into the postsynaptic membrane, thereby en-
Storage of information processed in the uni- hancing synaptic transmission over longer periods of
and polymodal association fields is the re- time (LTP).
336 sponsibility of the temporal lobe system (hip-
Despopoulos, Color Atlas of Physiology © 2003 Thieme
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