ChaPteR 8 Memory 285in human beings. And memories probably never
completely solidify, because the very act of re-
membering previously stored memories can make
them unstable again. A new round of consolidation
often then sweeps up new information into the old
memory, remolding it (Schiller & Phelps, 2011).Where Memories are Made LO 8.14
Scientists have used electrodes, brain-scan tech-
nology, and other techniques to identify the brain
structures responsible for the formation and stor-
age of specific types of memories. The amygdala
is involved in the formation, consolidation, and
retrieval of memories of fearful and other emo-
tional events (Buchanan, 2007; see Chapter 13).
Areas in the frontal lobes of the brain are especially
active during short-term and working memory tasks
(Goldman-Rakic, 1996; Mitchell & Johnson, 2009).
The prefrontal cortex and areas adjacent to the hip-
pocampus in the temporal lobe are also important
for the efficient encoding of pictures and words.
But it is the hippocampus that has the star-
ring role in many aspects of memory. It is criti-
cal to the formation of long-term declarative
memories (“knowing that”); as we have seen in the
case of H. M., damage to this structure can cause
amnesia for new facts and events. The hippocam-
pus is also critical in recalling past experiences
(Pastalkova et al., 2008).You are about to learn...
• some of the changes that occur in the brain
when you store a short-term versus a long-term
memory.
• where memories for facts and events are stored
in the brain.
• which hormones can improve memory.
the Biology of Memory
We have been discussing memory solely in terms
of information processing, but what is happening
in the brain while all of that processing is going on?
Changes in Neurons and
Synapses LO 8.13
Forming a memory involves chemical and struc-
tural changes at the level of synapses, and these
changes differ for short-term memory and long-
term memory.
In short-term memory, changes within neurons
temporarily alter their ability to release neurotrans-
mitters, the chemicals that carry messages from
one nerve cell to another (Kandel, 2001). In con-
trast, long-term memory involves lasting structural
changes in the brain. To mimic what they think may
happen during the formation of a long-term mem-
ory, researchers apply brief, high-frequency electri-
cal stimulation to groups of neurons in the brains of
animals or to brain cells in a laboratory culture. In
various areas, especially the hippocampus, this stim-
ulation causes receiving neurons at some synapses
to become more responsive, making certain synap-
tic pathways more excitable (Bliss & Collingridge,
1993; Lisman, Yasuda, & Raghavachari, 2012;
Whitlock et al., 2006). This increase in the strength
of synaptic responsiveness is known as long-term
potentiation. It is a little like increasing the diameter
of a funnel’s neck to permit more flow through the
funnel. During long-term potentiation, dendrites
also grow and branch out, and some types of syn-
apses increase in number (Greenough, 1984). At
the same time, in another process, some neurons
become less responsive than they were previously
(Bolshakov & Siegelbaum, 1994).
Most of these changes take time, which prob-
ably explains why long-term memories remain
vulnerable to disruption for a while after they are
stored, and why a blow to the head may disrupt
new memories even though old ones are unaf-
fected. Memories must therefore undergo a pe-
riod of consolidation, or stabilization, before they
“solidify” (see also Chapter 5). Consolidation can
continue for weeks in animals and for several years
long-term potentiation
A long-lasting increase
in the strength of syn-
aptic responsiveness,
thought to be a biological
mechanism of long-term
memory.consolidation The
process by which a long-
term memory becomes
durable and stable.Jennifer K. Berman