HUMAN BIOLOGY

the nerVOus system 257

hoW do memories form in the brain?

• Memories form when sensory messages are processed through
  short-term and long-term storage mechanisms.


• The storage mechanisms involve circuits between the
  cerebral cortex and parts of the limbic system, thalamus,
  and hypothalamus.

taKe-hoMe Message

amnesia The loss of fact

memory.

memory Storage of infor-

mation in the brain.

n Memory is how the brain stores and retrieves facts and

other types of information.

Learning and modifications of our behavior would be impos-

sible without memory. Memories develop in stages. The

first is short-term storage of bits of sensory information—

numbers, words of a sentence, and so on—for a few minutes

or hours. In long-term storage, seemingly unlimited amounts

of information get tucked away more or less permanently

(Figure 13.22).

Only some of the sensory information reaching the cere-

bral cortex is transfered to short-term memory. Information

is processed for relevance, so to speak. If irrelevant, it is

forgotten; otherwise it is consolidated with the banks of

information in long-term storage structures.

The brain processes facts separately from skills. Dates,

names, faces, words, odors, and other bits of explicit

information are facts that are stored together with the

circumstance in which they were learned. Hence you

might associate the smell of bread baking, say, with your

grandmother’s kitchen. This “fact” recall may be brief or

long-term and is called declarative memory. By contrast,

skill memory is gained by practicing specific motor activi-

ties. How to maneuver a snowboard or play a piano con-

certo is best recalled by actually performing it, rather than

by remembering the circumstances in which the skill was

first learned.

Separate memory circuits handle different kinds of

input. A circuit leading to declarative memory (Figure

13.23A) starts with inputs at the sensory cortex that flow

to the amygdala and hippocampus in the limbic system.

The amygdala is the gatekeeper, connecting the sensory

cortex with parts of the thalamus and with parts of the

hippocampus that govern emotional states. Information

flows on to the prefrontal cortex, where multiple banks of

fact memories are retrieved and used to stimulate or inhibit

other parts of the brain. The new input also flows to basal

nuclei, which send it back to the cortex in a feedback loop

that reinforces the input until it can be consolidated in

long-term storage.

Skill memory also starts at the sensory cortex, but this

circuit routes sensory input to a region deeper in the brain

that promotes motor responses (Figure 13.23B). Motor

skills entail muscle conditioning. The skill memory circuit

extends to the cerebellum, the brain region that coordinates

motor activity.

amnesia is a loss of fact memory.

How severe the loss is depends on

whether the hippocampus, amygdala,

or both are damaged, as by a head

blow. Amnesia does not affect a per-

son’s capacity to learn new skills.

Memory

Figure 13.22 Memories are processed in two stages.

Short-term memory is temporary. Long-term memories

may be stored in the cerebral cortex for years.

Input forgotten

Recall

of stored

input

Emotional state, having time

to repeat (or rehearse) input,

and associating the input

with stored categories of

memory influence transfer

to long-term storage

Short-term Memory

Input irretrievable

Sensory stimuli, as from

the nose, eyes, and ears

Temporary storage in

the cerebral cortex

Long-term Memory

Figure 13.23 Memories of facts and skills are stored

differently. a Possible circuits involved in declarative memory.

B A snowboarder provides a dramatic demonstration of

skill memory.

B

13.10

smell

A amygdala hippocampus

thalamus and

hypothalamus

basal nuclei

touch

hearing

vision

prefrontal cortex

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