Rewire Your Brain: Think Your Way to a Better Life

declarative memory.
The recall of language - based 
information is called
semantic memory
. Overlapping memories about 
your past are referred to as
episodic memory.
These types of explicit 
memory are distinguishable as follows: If you remember getting a 
paper cut, that ’ s episodic memory. If you remember the facts about 
how you got the paper cut, that ’ s declarative memory. If you remem-
ber the words you used when telling someone about the paper cut, 
that ’ s semantic memory. 
If the episodic memories involve strong emotions, they are referred 
to as
emotional memory.
Habitual styles of moving, such as riding a 
bicycle or writing your name, are called
procedural memory.
Although all these memory subsystems are considered forms 
of long - term memory, they can be regrouped as two large subsys-
tems,
explicit
and
implicit
memory. This distinction is important for 
your understanding of how to cultivate your memory skills. Explicit 
memory involves facts and declared experiences. Implicit memory 
involves procedural skills and emotional memory. The components 
of the two kinds of memory are shown below. 
Explicit Memory
 Implicit Memory 
•
Declarative
•
Procedural
•
Semantic
•
Emotional 
•
Episodic
Some implicit memories, such as emotional memory, are acquired 
rapidly, such as being traumatized by assault, whereas procedural 
memories, such as the learned ability to play the cello, are acquired 
only with painstaking repetition. 
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76 Rew i r e
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The hippocampus, which is largely responsible for encoding 
explicit memories, generates thoughts from previous learning and 
information. If you didn ’ t have that ability, then every day would be 
a new day — literally. That might, for a moment, sound good, but it is 
not. For example, Henry Molaise, one of the most famous patients in 
the history of neurology and neuropsychology (he is called “ HM ”
in the research literature), taught us a lot about the hippocampus 
and explicit memory. 
Henry lost the ability to consolidate new explicit memories after 
he had brain surgery as a young adult. He had been hit by a car 
when he was nine years old and had begun having medically intrac-
table seizures, so a neurosurgeon removed Henry ’ s right and left 
hippocampus in 1953 to try to control the seizures, before the role 
of the hippocampus was well understood. After this surgery, Henry ’ s 
seizures got better but he could not remember people. If he was 
introduced to a stranger and chatted amiably with him, and the 
visitor then left the room for a few minutes and came back, Henry 
would not remember having ever seen the person before. 
Henry remained capable of remembering events from long ago and 
of forming procedural memories, however. For instance, he could 
walk around the block and remember how to get home — not explic-
itly, but in a procedural way. He could be taught a certain movement 
and, when asked to make that movement again later, could do so 
with greater facility than when he fi rst learned it, but he would have 
no recollection of having ever performed the task before. 
Through the many evaluations performed by neuropsychologist 
Brenda Milner, neuroscience discovered that the hippocampus is 
centrally involved in the laying down and retrieval of memories of 
past experiences. The hippocampus is necessary for consolidating 
an explicit memory about a situation that arises in our current life, but 
not for recalling the events associated with an old autobiographical 
memory. 
The health of the hippocampus plays a central role in aging. Later 
in life there is a gradual atrophy of the hippocampus. 
Many Alzheimer ’ s patients lose declarative memory while, like 
Henry, retaining parts of their procedural memory. They continue to 
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C u l t i va t i n g
M e m o r y
77
perform procedural memories out of habit while having an increased 
diffi culty remembering recent facts about their lives. 
Emotionally signifi cant events are more likely to be remembered 
in the long run not only because they hold more personally meaning-
ful themes but also because they are associated with higher levels of 
arousal. Emotional events stir a physiological reaction, including an 
increase in the level of blood glucose, which promotes the process 
of memory consolidation. 
Emotional events resonate in your mind, creating neuroplas-
tic change and enhancing memory consolidation. If you want to 
remember something, become emotionally involved in it. You ’ re 
more likely to remember emotionally signifi cant events not only 
because they hold more personally meaningful themes but because 
they are associated with higher levels of arousal. 
The emotional memory ’ s neural networks can often be associ-
ated with the experience of fear. As I noted in chapter 2 , classically 
conditioned fear responses to auditory and visual stimuli are medi-
ated by the subcortical pathways that connect the thalamus (the 
central switchboard of the brain) to the amygdala. In other words, 
as researcher Joseph LeDoux of New York University has noted, 
“ This circuit bypasses the cortex and thus constitutes a subcortical 
mechanism of emotional learning. ”
Despite the importance of the amygdala in emotional learning, it 
appears to play no signifi cant role in most declarative memory pro-
cesses. The cortex, in contrast, is unnecessary for the acquisition of 
conditioned fear, but it is essential for the extinction of conditioned 
fear. In other words, fear can be conditioned without your aware-
ness but cannot be eliminated without it. The cortex is also critically 
important in taming the amygdala to conquer anxiety. 
The power of emotional conditioning varies, based on your state 
at the time. If the norepinephrine level is high, conditioning occurs 
more rapidly, and the conditioned response not only is learned more 
quickly but also lasts longer. 
Like most animals, you can learn tasks that require the activation of 
your amygdala but not of your hippocampus. On the other hand, you 
can ’ t learn tasks that require the hippocampus but not the amygdala. 
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The amygdala activates generalized attention and mobilizes the 
entire brain - body system through its interactions with the HPA 
axis. You are able to store episodic memories even when emotional 
arousal is not a component of an incident. When your brain is work-
ing well, the amygdala sets up the emotional state that is optimal 
for memory. Later, when you are once again in that emotional state, 
you are more likely to remember explicit material that is congruent 
with that state. 
You typically have few explicit memories of the fi rst three or fi ve 
years of your life. Sigmund Freud inaccurately referred to this phe-
nomenon as