Lesson 10. Learning and Memory

Localization of Memory

There are three basic approaches.

1. Imaging. Modern imaging techniques like fMRI (functional magnetic resonance imaging) or

PET (positron emission tomography) allows one to “see” areas of the brain that are active during

specific brain tasks. If a subject is placed in an fMRI scanner and given a memory test, one can

determine what areas of the brain are active, and that activity presumably is related to where in

the brain the memory is processed and/or stored.

The figure above illustrates an example of a PET scan of an individual who is performing

an object location test. The color code is such that the brighter, redder regions indicate increased

brain activity. The most active region is the hippocampus. In discussions of memory, the

hippocampus is mentioned repeatedly because it is a major part of the brain involved in

declarative memory function. This illustration clearly indicates that the hippocampus is involved

in object location memory. But as we will see soon, it is not where all memories are stored.

2. Brain lesions. In this experimental procedure, small parts of the brains of mice or rats are

surgically removed or chemically inactivated and the animals are systematically examined to

determine whether the lesion affected any memory system.

3. Brain disease and injury. Here scientists take advantage of individuals who have had

unfortunate brain injuries, for example, through stroke or through a brain tumor in a specific area

of the brain. If one finds a memory deficit in the patient, it is likely that the region of the brain that

was injured is involved in that memory.

The figure below summarizes many decades of research on the anatomical locus of

memory systems. The medial temporal lobe and structures like the hippocampus are involved

with memories for facts and events; the striatum is involved with memories for skills and habits;

the neocortex is involved with priming; the amygdala is involved with emotional memories; and

the cerebellum with simple forms of associative learning. Lower brain regions and the spinal cord

contain even simpler forms of learning. In summary, memory is not stored in a single place in the

brain. It is distributed in different parts of the brain.

Lesson 11. Types of Memory

Psychologists and neuroscientists have divided memory systems into two broad

categories, declarative and non-declarative. The declarative memory system is the system of

memory that is perhaps the most familiar. It is the memory system that has a conscious

component and it includes the memories of facts and events. A fact like 'Paris is the capital of

France', or an event like a prior vacation to Paris. Non-declarative memory, also called implicit

memory, includes the types of memory systems that do not have a conscious component but are

nevertheless extremely important. They include the memories for skills and habits (e.g., riding a

bicycle, driving a car, playing golf or tennis or a piano), a phenomenon called priming, simple

forms of associative learning [e.g., classical conditioning (Pavlovian conditioning)], and finally

simple forms of non-associative learning such as habituation and sensitization. Declarative

memory is "knowing what" and non-declarative memory is "knowing how".

Everyone is interested in knowing how well they remember so let us take a simple memory

test. This test will present a list of 15 words (see photo below), then there will be a pause and

you will be asked whether you remember some of those words. You have to put your pen down

for this test.

This memory test called the DRM test after its creators James Deese, Henry Roediger

and Kathleen McDermott. It was not meant to be a trick, but to illustrate a very interesting and

important feature about memory. We like to think that memory is similar to taking a photograph

and placing that photograph into a filing cabinet drawer to be withdrawn later (recalled) as the

“memory” exactly the way it was placed there originally (stored). But memory is more like taking

a picture and tearing it up into small pieces and putting the pieces in different drawers. The

memory is then recalled by reconstructing the memory from the individual fragments of the

memory. The reason so many individuals incorrectly believe that “sweet” was on the list is

because there were so many other words on the list that had a sweet connotation. “Failing” this

test is actually not a bad outcome. Individuals with Alzheimer’s disease generally do not say that

“sweet” was on the list. They cannot make the normal associations involved in the recall of a

memory.

The word list gives insights into memory processing and retrieval, but it is not a really good

test of “raw” memory ability because it can be affected by distortions and biases. To avoid these

problems, psychologists have developed other memory tests. One is the object recognition test

to test declarative memory. This test is also good because it can even be used on animals. The

test involves presenting a subject with two different objects and they are asked to remember those

objects. There is a pause and then two objects are shown again, one of which is new and the

other having been shown previously. Subjects are asked to identify the novel object, and to do

so, they need to remember which one was shown previously. A somewhat related test is the

object location test in which subjects are asked to remember the location of an object on a two-

dimensional surface.

Examples of non-declarative memory, such as associative learning, can be tested by

pairing one stimulus with another and later testing whether a subject has learned to make the

association between the two stimuli. The classical example is the paradigm developed by the

Russian physiologist Ivan Pavlov, which is now called classical or Pavlovian conditioning. In

classical conditioning, a novel or weak stimulus (conditioned stimulus, CS) like a sound is paired

with a stimulus like food that generally elicits a reflexive response (unconditioned response, UR;

unconditioned stimulus, US) such as salivation. After sufficient training with contingent CS-US

presentations (which may be a single trial), the CS is capable of eliciting a response (conditioned

response, CR), which often resembles the UR (or some aspect of it).

Lesson 12. Types of Amnesia

A classic study on localization of memory was the result of surgery performed on Henry

Molaison, a patient who was only known to the scientific community as “H.M.” until his death in

2008. H. M. is famous in neuroscience literature because his brain provided major insights into

the localization of memory function. In the 1950’s, H.M. was diagnosed with intractable epilepsy,

and while there are pharmacologic treatments, in some cases the only treatment is to remove the

portion of the brain that is causing the seizures. Consequently, H.M.'s hippocampus was removed

bilaterally. The figure on the right is an MRI of a normal individual showing the hippocampal

region, whereas the figure on the left shows a MRI of patient H.M. after the removal of the

hippocampus.

Before the operation, H.M. had a fine memory, but after the operation, H.M. had a very

severe memory deficit. Specifically, after the operation H.M.'s ability to form any new memories

for facts and events was severely impaired; he had great difficulty learning any new vocabulary

words; he could not remember what happened the day before. So if H.M. had an interview the

day following a previous interview, he would have little or no memory about the interview or events

during it. This study clearly indicated that the hippocampus was critical for memory formation. But

whereas H.M. had great difficulty forming new memories for facts and events, he still had all of

his old memories for facts and events. Specifically, he had all his childhood memories, and all of

his memories prior to the operation. This type of memory deficit is called anterograde amnesia.

(In contrast, retrograde amnesia refers to loss of old memories.) The studies on H.M. clearly

indicated that whereas the hippocampus is critical for the formation of new memories, it is not

where the old memories are stored. It is now known that those old memories are stored in other

parts of the brain, such as in the frontal cortex. The process by which an initially labile memory is

transformed into a more enduring form is called consolidation. This process involves the memory

being stored in a different part of the brain than the initial site of its encoding.

H.M. was also interesting in that while his ability to form new memories for facts and events

was severely impaired, he could form new memories for skills and habits. While he could form

new memories for skills and habits, he did not know that he had the skills! He had no awareness

of the memory; he couldn’t declare that he had it. This finding clearly indicated that the memory

for skills and habits are not formed in the hippocampus. Collectively, we learned from these

studies on H.M. and other patients that memory is distributed throughout the nervous system, and

different brain regions are involved in mediating different types of memory.