Download Disorders of Memory

Clinical Memory Failures
Chapter 7 – part 2
(Pgs. 173 – 173)
Amnesia
Loss of memory facts, events, information
and/or experiences that is not accounted for by
problems with attention, perception,
language, reasoning, or motivation. People with
amnesia typically are lucid and maintain a sense
of self, but they face severe difficulties in
learning new information and forming new
memories and/or they may not be able to recall
memories of past experiences.
Causes
Amnesia may result either from
organic or neurological causes (damage to the
brain through physical injury, neurological
disease or the use of certain drugs), or
from functional or psychogenic causes
(psychological factors, such as mental disorder,
post-traumatic stress or psychological defense
mechanisms).
The hippocampus
Part of the limbic system located in the Medial
Temporal lobe (MTL).
Hippocampus
Required to form new explicit (semantic and
episodic) memories. (1) It is a temporary store
for new memories, which are later consolidated
and transferred to the cerebral cortex, and (2) it
is responsible for generating coding schemes
(like a database index or file compression
"dictionary") to support efficient, compact, and
organized representations in the cerebral cortex.
Retrograde (RA) and Anterograde (AA) Amnesia
• Both RA and AA can occur together in the
same patient and is called Global Amnesia
(e.g., HM).
• AA is the more common type of amnesia.
Pure RA is rare.
Retrograde Amnesia
A person's pre-existing memories are lost to
conscious recollection, beyond an ordinary
degree of forgetfulness, even though they may
be able to encode and retrieve new experiences
that occur after the onset of amnesia.
Areas of the Brain
that play a role in RA
Already existing long-term memories are stored
in the neurons and synapses of various different
brain regions. RA is associated with damage to
the Prefrontal Cortex and Temporal Cortex
(include the hippocampus)
Tests For Retrograde Amnesia
Boston Remote Memory Test
Famous Faces
Free recall portion: patients asked to
recall the name of the person shown
in the photograph (e.g., Telly
Savalas). Participants were given
ample time to respond.
If they were unable to recall the
name, were given a series of cues.
First, a semantic cue was given (e.g.,
"He was an actor, American, and had
a popular series on TV").
If semantic cue fails a phonemic cue was given
(i.e., the person's initials).
Four answer, forced choice test.
(e.g., Yul Brynner, David Soul, Don Rickles, or
Telly Savalas).
Past Public Events Test
Performance measured with a free recall test
(e.g., "Who killed John Lennon?") and a fouralternative, forced-choice recognition test
(names of individuals such as John Hinkley, Sara
Jane Moore, David Roth, or Mark Chapman).
Both of these tests involve Semantic (fact based)
as well as episodic memory.
Evidence of Temporal Gradient in RA
Source: Haist et al, 2001
Participants (50+ years old) healthy (control)
and RA patients were shown pictures of famous
faces and asked if they can identify them
The famous faces belonged to people that
reached prominence in many different decades
Results: Controls have comparable memory for
faces across all decades. RA patients are
particular bad at remembering celebrities from
more recent decades.
RA patients could remember older memories as
well as healthy patients.
RA and Types of LTM
Typically, episodic memory (including
autobiographical memory) is more severely
affected than semantic memory, so that the
patient may remember words and general
knowledge (such as who their country’s leader
is, how everyday objects work, colors, etc.) but
not specific events in their lives.
What remains Intact?
In general, implicit memory tasks do not differ
between healthy participants and amnesiacs.
Often have intact procedural memory!
Procedural memories (memory of skills, habits
and how to perform everyday functions) are
typically not affected at all.
Procedural memory is often implicit rather than
explicit (i.e., we know how to do things without
knowing how we learned to do that skill or
when we learned it.)
Interesting Example
Two experienced drivers who developed severe amnesia due to
bilateral hippocampal lesions participated in a series of
standardized challenges of driving performance and knowledge
of driving rules. During drives in a high fidelity simulator and on
the road in an instrumented vehicle, they demonstrated vehicle
control similar to that of normal drivers on measures of steering,
speed control, safety errors, and driving with distraction. Their
knowledge of driving rules, safety procedures, and road sign
meaning also was normal. However, both participants were
impaired at following route directions, and both had unsafe
responses in a difficult crash avoidance scenario on the
simulator. These findings suggest that memory impairment
acquired by experienced drivers does not impair most aspects of
driving performance, but may increase safety risk under some
challenging circumstances. (Anderson et el., 2007)
RA and Semantic Memory
Typically RA patients retain their long-term semantic
memory (i.e., they remember how to use language,
general knowledge etc.). This is because the
hippocampus is necessary to first acquire new semantic
information (Gabrieli, Cohen, & Corkin, 1988), but these
representations are then consolidated in the neocortex
and become independent of the hippocampus with time
(McClelland, McNaughton, & O'Reilly, 1995). Remote
semantic memory is considered independent of the
hippocampus, and the hippocampus is not thought to
play a critical role in the processing and use of such
representations.
RA is not necessarily a permanent
condition
Memory for various events may return. Usually
the older memories return before more recent
experiences. This has been referred to as a
shrinking retrograde amnesia. The shrinkage is
not complete as events occurring seconds or
minutes before the trauma may be permanently
forgotten.
Anterograde Amnesia
The ability to memorize new things is impaired
or lost because information does not
consolidate into permanent LTMs.
Areas of Brain
that play a role in AA
Temporal Lobes
Hippocampus
Diencephalon
A cluster of subcortical structures in the center
of the brain. For memory, the most important
are the thalamus and the mammillary bodies.
Implicit Learning in AA patients
Claparede study (1911).
– Patient never remembered
having met Claparede (doctor)
before
– Claparade offers handshakes
with pinprick
– Next time, no explicit memory
of event (or doctor)
– Still, patient refuses to shake
hands and offers explanation:
“sometimes pins are hidden in
people’s hands”
What Does it Feel Like to be Amnesic?
Video
Implicit Memory and Amnesia
Degraded Picture Test
Elizabeth Warrington
Amnesias show impaired
explicit memory but much
less impairment of implicit
memory.
GP Mem(1)
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HM able to mirror trace
improvement in H.M. for mirror tracing task (without
conscious recollection of previous training episodes)
 the medial temporal lobes are not necessary for all
types of long-term memory.
Milner, 1965
+
Semantic vs. Episodic Memory
• While all AA patients have profound
deficits in episodic memory, many have
only minor (if any) semantic impairments:
– Spiers, Maguire, & Burgess’s (2001) reviewed
147 cases.
– Vargha-Khadem’s (1997) patients, Jon and
Beth (impaired as children but developed
normal semantic memories).
+
Vargha-Khadem’s (1997)
Global anterograde amnesia is described in three
patients with brain injuries that occurred in one
case at birth, in another by age 4, and in the third at
age 9. MRIs showed bilateral hippocampal damage
in all three cases. Remarkably, despite their
pronounced amnesia for the episodes of everyday
life, all three patients attended mainstream schools
and attained levels of speech and language
competence, literacy, and factual knowledge that
are within the low average to average range.
Psychogenic Amnesia
(functional or dissociative)
- severe stress or psychological trauma
Global amnesia - (fugue state)
- sudden loss of personal identity
- severe stress or depression
- extended periods of wandering and confusion.
Very rare, and usually resolves over time (although
memory of the fugue episode itself may remain
lost).
Situation-specific amnesia
- type of psychogenic amnesia that occurs as a
result of a severely stressful event.
- normal autobiographical memory processing
blocked by imbalance of stress
hormones (e.g.,Cortisol) particularly in the
regions of the limbic system.
Alzheimer’s
e.g., Ronald Reagan
Degenerative Disorder - slow decline in memory,
thinking and reasoning skills.
The Brain and Alzheimer’s Disease
Two major structural changes:
Plaques – bundles of proteins that develop in the
synaptic space disrupting communication between
neurons.
Tangles – Tau protein fibers that develop in the
neurons’ nucleus decreasing neural functioning.
tangle
plaques
Over time
massive cell loss
dramatically
reduces brain
mass!
http://www.alz.org/brain/14.asp
Hippocampus
Disruption of neural functioning generally begins
in the hippocampus, thus memory impairment
is one of the first signs of the early stages of
Alzheimer’s.
Risk Factors
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Obesity
High blood pressure
Head trauma
High cholesterol
Being American!
– Higher rates in
• Japanese-Americans than Japanese
• African-Americans than Africans
• Depression
• Lower rates in highly educated
– Beneficial consequences of learning and memory
Possible Protective Factors
Education
The ability of the brain to change suggests to some that
staying mentally active as you age may help to maintain
healthy brain synapses. A 2002 study reported an
association between frequent participation in cognitively
stimulating activities (such as reading, doing crossword
puzzles, visiting museums) and a reduced risk for
Alzheimer's.
Exercise
Lowers risk of high blood pressure and other risk factors associated
with Alzheimer’s
Alcohol Consumption
Men who consume one to three drinks of alcohol per day cut their
risk of developing the disease by nearly half. Among women,
however, the risk was reduced by only 4%. The type of alcohol had no
effect on the results. But further study is needed. In the meantime,
experts do not recommend drinking alcohol to fend off Alzheimer's
disease.
Source: Harvard Health Publication
Infantile Amnesia
Lack of autobiographical memory for events
prior to 5 years of age (age varies).
Infantile Amnesia
Sheingold and Tenney (1982):
– Participants:
• College students and children (ages 4–12)
– Task:
• Answer specific questions about a sibling’s
birth from when they were 3–11 years old
– e.g. “Who took care of you while your mother was
in the hospital?”
• Mothers were asked the same questions
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Results:
If the birth occurred after 3 years old, very little
forgetting occurred even if it occurred many
years ago
If birth occurred before 3 years, virtually nothing
was remembered
Limited to Episodic Memory
Infantile amnesia is limited to episodic memory.
Infancy is a time of remarkable learning,
including motor skills, language, semantic facts.
That learning is not lost – but it is implicit.
Why?
The hippocampus and surrounding MTL which is
responsible for LTM is not fully developed.
Hippocampus is not fully formed until about 2
years of age.