ECT: Facts and Myths
about the treatment method
Date: Tuesday, January 28 @
14:21:35 SAST
Topic: SA Family Practice
Convulsive therapy, using chemical inductions, was
introduced by Ladislas Meduna in 1934.In 1938, the
Italians Ugo Cerletti and Luigi Bini described an easier
induction by using electrical impulses.
Dr LP Steenkamp
MBChB, Hons BSc Pharm, MFGP, MSAIP, MISCEH,
FC Psych CMSA), MMed(Psych) (End Forensic
Psych)
Medical Superintendent & Director: Denmar
Hospital
Consultant to Dept of Psychiatry: University
Pretoria
International Member of the American
Psychiatric Association:
Member of the Association for C.T. |
For you must know why the
public, doctors and even some psychiatrists are sceptic
and afraid of the treatment method.
Convulsive therapy, using
chemical inductions, was introduced by Ladislas Meduna
in 1934.In 1938, the Italians Ugo Cerletti and Luigi
Bini described an easier induction by using electrical
impulses. Within a decade, electroconvulsive therapy
(ECT) was hailed as the main treatment of hospitalised
mentally ill patients. It was used extensively
world-wide at the same time as insulin coma and
leucotomy. However, the introduction of the psychoactive
medicines in the 1950’s led to the rapid abandonment of
the treatment. The treatment method re-emerged in the
1970’s when psychiatrists sought ways to help the
mentally ill who were unresponsive to medication and
psychotherapies. These “therapy resistant” cases pleaded
for any useful intervention, and practitioners who had
used ECT earlier but discarded their devices in the
enthusiasm for psychotropics, recalled their experience
and offered ECT again. Their success led to a renewed
interest in the procedure.
Background
Despite sixty-eight years of acknow-ledged high efficacy
and safety in the treatment of depressive and psychotic
illnesses, ECT continues to generate controversy in the
media, with limited use mainly in academic and private
hospitals. The dismay results from attack by the
“anti-psychiatry movements”, people’s misbeliefs and the
guarded support by some health professionals.
Belief that the treatment
affects the brain, arouses primitive fears that the soul
of the individual, one’s inherent individuality and
uniqueness, is affected. And the media often portrayed
the treatment, as it was first perceived in the movies
The Snake Pit (1948), Fear Strikes Out (1957), Shock
Corridor (1963) and Shock Therapy (1964) - patients
being forced to receive treatment against their will,
and used by Svengali-like psychiatrists to control the
exited and aggressive behaviour of maniacs.
Furthermore, the very terms electro-shock and
electroconvulsive treatment raise the specter of
electrocution, and electric chair that ends the lives of
murderers.
These misperceptions, preconceived ideas and personal
prejudices however are not enough to sustain the
controversy. It is also fueled by the persistent
activities of the Antipsychiatry Movements. The
movement is led by the Citizen’s Commission on Human
Rights an establishment of the “Church of
Scientology” organised in 1969 in California (USA).
These polemicists targeted ECT as sensitive and
vulnerable with mixed support from the media and some
health professionals. The target was suitable because
the lay media portrayed it as used by oppressive
physicians, who would without patients’ consent, force
treatment on them as a form of punishment.
Horror money-making movies like
A Woman Under the Influence (1974), One
Flew Over The Cuckoo’s Nest (1975), The Fifth
Floor (1980), Frances & Death Wish II
(1982), Return to Oz (1985), An Angel at My
Table (1990), Heavenly Creatures (1994),
Angel Baby (1995), Lilac’s Story
(1995), Cosi (‘96) and Shine (1996)
reflected this view.
The movement was and is encouraged by
pseudophilosophical psychiatrists like Thomas Szasz
& Ronald Laing who argued that there were no
mental ill-nesses, merely maladaptive relationships to
society.
The “Scientologists” seemingly perceive
psychiatrists and psychiatric treatment methods as
unfair competition in their quest to convince men rather
to buy into the salvation they promise. Their
vocal members are frequent speakers in afternoon
talkshows on radio and TV where the hosts encourage a
circus atmosphere rather than reasoned discourse.
The “Citizen’s Commission on Human Rights”
assisted by some department officials, are still
actively trying to persuade the Minister of Health to
outlaw ECT in the RSA.
Negative perceptions held by some mental health
professionals usually reflect there
- Allegiance to a faith in the psychological basis
of mental illness; or
- Preconceived and subjective belief that the
public perception of brain damage is indeed true; or
- Discomfort with a psychiatric practice that
calls on medical experience and the laying on of
hands; or
- Ill aquaintedness with the treatment i.e. lack
of experience and scientific knowledge.
This turmoil however has had
profound effects on the use of the treatment method and
because of it, may lead to years of needless suffering
as patients are given a lengthy series of ineffective
medication trials before ECT is considered.
“Politicalisation” of the treatment method has also
resulted in the fact that in South Africa, as in the
USA, Canada and the U.K., more than 90% of the
recipients are from the high income groups or Caucasion.
Access to ECT is most limited for patients who have to
make use of public facilities.
On the positive side the controversy has led to
extensive renewed research, ultra modern apparatus,
and safety monitoring devices, specific guidelines and
detailed methods to reduce medical risks - all to
the benefit of the patient.
WHAT ARE THE REAL FACTS ABOUT ECT?
In order to assist and inform possible recipients and
their families, answers are given to the most frequent
questions asked about the treatment method.
What are the indications for the use of ECT, or,
in other words, which illnesses respond favourably to
ECT?
The General Indications are:
1. Major Depressive Disorders
The primary indication for ECT is major depression,
especially endogenous depression or melancholia with the
classical symptoms of sadness or pronounced apathy, loss
of appetite and weightloss, constipation, loss of sexual
interest, early morning wakening, agita-tion or
retardation, emotional emptiness, and ruminations of
guilt, worthlessness, hopelessness, death, or suicide.
ECT is especially the treatment of preference when
depression has rendered the person psychotic (mentally
disturbed or stuporous), physically ill, unable to care
for him/herself, or dangerous to him/herself or others.
The response of melancholia is excellent in both bipolar
and unipolar depression. Patients with melancholia are
often contrasted with reactive, neurotic, or dysthymic
depres-sives whose illness is generally poorly or
transiently responsive to ECT and who exhibit self-pity,
anxiety rather than sadness or apathy, tendencies to
blame others, a scarcity of physiological features, and
no distinct onset.
How effective is ECT in the treatment of Major
Depression?
Very effective! All present day pro-spective
controlled, double-blind, randomised comparisons of ECT
versus antidepressants in the treatment of
depression favour ECT1.
Most pertinent to modern practice however, is the
effectiveness of ECT for patients who do not respond to
medications: Almost 1/3 of endogenous depressives fails
to respond to adequate 8-10 week medication and
combinations trials. In contrast recent outcome data
from 4 leading ECT centres, using strict research
criteria, demonstrated an 86% efficacy rate for ECT.
2. Schizophrenia
ECT is also indicated for schizophrenia with acute
exacerbation, expressed as excitement, overactivity,
hallucinations, delusions, and intense emotional
expression (eg. fear, suspicion), emotional lability,
altered sensorium (clouding of conscienceness), or mood
swings. In contrast it is generally believed that
chronic schizophrenia without recent aggravation of
positive symptoms (as aforementioned) does not exhibit
sustained benefit from ECT but that in such patients a
trial of ECT can nevertheless be justified if
chemotherapy does not restore the patient to his/her
best recent functional level, and that ongoing
neuroleptic dosages can often be reduced by doing so.
This scenario however has changed drastically over the
past ten years in favour of the use of ECT in chronic or
so-called neuroleptic resistant schizophrenia.
How effective then is ECT in Acute and Chronic
Schizophrenia?
Antipsychotics are believed to be the mainstay of
somatic treatment for patients with schizophrenia, but
well-controlled comparisons of ECT versus neuroleptics
found the treatment outcome in acute schizophrenia to be
equivocal and equipotent. Nonetheless, recent acute
treatment trials with neuroleptics found a substantial
clinical benefit in only ~50% of patients. Furthermore,
the relapse/recurrence rate in neuroleptic responders is
as high as 78% during a 2 year follow-up period. The
issue of treatment-resistant schizo-phrenia (TRS)
further complicates care of these patients. This refers
to a subgroup of patients, estimated to be ~10-40%, who
do not or only partially respond to neuroleptic (i.e.
typical or atypical) treatment. Research on the use of
ECT in TRS has concluded that:
- Combined ECT and neuroleptic therapy effectively
reduced psycho-tic symptoms in 57% of
treatment-resistant patients with schizophrenia.
- ECT and neuroleptic treatment are more effective
than either ECT or Neuroleptic treatment alone,
pro-bably by synergistic effects.
- ECT alleviates both positive and negative
symptoms in schizophrenia.
- Improvement can be maintained with
Continuation-ECT and neuroleptic therapy.2
3. Mania
Manic episodes usually form part of a Bipolar
Affective Disorder. Specific criteria must be met
before the diagnosis is made namely:
A distinct period of abnormally and persistently
elevated, expansive, or irritable mood lasting at least
1 week. During the period of mood disturbance, 3 (or
more) of the following symptoms have persisted (4 if
mood is only irritable) and have been present at a
significant degree.
- Enflated self-esteem or grandiosity.
- Decreased need for sleep.
- More talkative than normal or pressure to keep
talking.
- Flight of ideas or subjective expe-rience that
thoughts are racing.
- Distractibility.
- Increase goal-directed activity or psychomotor
agitation.
- Extensive involvement in pleasurable activities
that have a high potential for painful consequences
(e.g. unrestrained buying sprees, sexual
indiscretions, or foolish business investments).
The mood disturbance must be
sufficiently severe to cause marked impairment in
functioning and not due to a substance or a general
medical condition.
Is ECT effective in normalising this condition?
Yes, clinical and research investigations over five
decades indicate that ECT has robust anti-manic effects.
ECT is more effective than
lithium-neuroleptic combinations in the rapid
resolvement of the mood disorder. What is even more
impressive is that ECT brings about marked clinical
improve-ment or full recovery in 80% of manic patients
non-responsive to pharmaco-therapy. Maintenance - ECT as
an outpatient in refractory Bipolar Disorder also result
in significant reduction of health care costs. In the
manic-psychotic person it is of utmost importance to
restore normal mood and functioning before blatant
social indiscretions or major financial losses are
incurred. ECT should therefore be regarded as a
first-line treatment for acute mania.3
4. Acute Delirious States
What is meant by “delirium” and how does it present
itself?
Acute delirium is defined as a clinical condition
characterised by disorien-tation, clouding of
consciousness, anxiety, sleeplessness, hyperactivity,
and exaltation, possibly with hallucinations and
delusional ideas. Secondary to these symptoms, the
patients often refuse to eat and drink, and as the
agitation increases, become dehydrated, develop high
temperatures, an increased pulse rate and blood
pressure, followed by circulatory collapse. The problem
may arise from a physical illness or condition e.g.
systemic infection, endocrine disorder, after childbirth
or severe physical trauma or toxicity from exogenous
substances. It can also develop as a feature in severe
affective disorder, acute transient psychotic disorder,
or schizophrenia.
Since we picture confusion and impaired memory as
part of the ECT process and anticipate worsening of the
clinical situation, is ECT really safe and effective to
use in such conditions?
Most certainly! Treatment of acute delirium
with sedatives and neuroleptics is rarely effective, and
without specific treatment patients experience stuporous
exhaustion, systemic shock and cardio-vascular collapse.
Death can occur in the course of a few days or even
hours. In many instances young people with a long life
expectancy experience acute delirium. Before the use of
ECT, more than 80% of patients with “delirium acutum”
died of their disease. After the introduction of ECT
practically all survived and recovered completely in the
course of a few days.4
5. Medical Conditions
- Secondary catatonia
- Neurolept malignant syndrome
- Intractable seizures and status epileptics
- Parkinson’s disease
- Hypopituitarism
The 1990 APA Task Force on
ECT (supported more or less by The Second Report of the
Royal College of Psychiatrists’ Special Committee on
ECT) further made the following recommendations
regarding the indications for ECT:
A. Primary use of ECT
- Need for a rapid definitive response.
- Risks of other treatments outweigh ECT risks.
- History of poor medication response.
- History of good ECT response.
- Patient preference.
B. Secondary use of ECT
- Antidepressant treatment failure.
- Adverse or intolerable side-effects of
medication.
- Deterioration in condition increases need for
Rapid Response (i.e. refusing food / fluids).
C. Continuation and
Maintenance ECT
- Recurrent illness with acute & good ECT
response.
- Medication non-responsiveness or intolerance.
- Ability to comply, voluntary.
How safe or risky is
the treatment method in general?
ECT is amongst the safest and least risky medical
procedures carried out under induction anaesthesia. To
put the mortal risk with ECT in proper perspective, it
is only necessary to note that ECT is about 10 times
safer than childbirth. One large scale Scandinavian
survey found one death in 22,210 treatments for a per
treatment mortality rate of 0.004%. Recent figures from
the state of California reflected 2 deaths per 99,425
treatments, for a per treatment mortality rate of
0.002%5 and are at the bottom of the reported range for
anaesthesia induction alone (0.003% to 0.04%).
The American Psychiatric Association and the
Royal College of Psychiatrists recognise no
contra-indications to ECT. The same view is held by the
South African Society of Psychiatrists.
As in all anaesthesias the greatest risks are in people
with severe or un-stable concomitant medical conditions.
How safe is it for people suffering from
heart disease?
Good question! Complications like for instance acute
myocardial infarction and conduction disturbances are
responsible for most of the mortality associated with
anaesthesia and said to be for the treatment method,
although none of these were reported in the Scandinavian
survey cited above. Caution is required in patients with
heart problems and the underlying condition should be
treated effectively beforehand, however the decision to
administer ECT will then be, as always, a matter of
informed consent by the patient with due consideration
of the risks of giving or not giving ECT, bearing in
mind that 10-15% of untreated or medicine-non-responsive
severe depressed people commit suicide.
What if I suffer from high blood pressure?
However severe, high blood pressure does not disqualify
a person from getting ECT. The treatment even improves
high blood pressure in men6. Probably because
the transient ECT-induced blood pressure rise lasts for
only miennutes, stroke is very rare during ECT. Among
patients who received ECT for post-stroke depression,
86% improved markedly and none showed new neurological
symptoms or worsening of old ones, although several
strokes were less than one month old7.
If I have an aneurysm, what then?
There are numerous published reports of the uneventful
use of ECT in patients with aortic aneurysm, either
before or after repair. Untreated brain aneurysms that
have bled have a tendency to rebleed, and therefore
present a distinct risk with ECT. After surgical
correction blocking agents should prevent the
short-lived ECT-induced rise in blood pressure.
Can it be given to someone with a brain
tumour?
ECT should be avoided where intra-cranial pressure is
increased. However, tumours without increased pressure
have not been reported to increase the risk with ECT8.
Does a scull defect exclude me from having
ECT?
As result of previous injury or brain surgery defects in
the bony structure may occur, but this does not exclude
a person from getting the treatment if needed. Special
care only has to be taken in the placement of the
electrodes during treatment.
I’m pregnant and severely depressed, can I
have ECT during my pregnancy?
Most definitely! Numerous studies amply support the use
of ECT during pregnancy. Sophisticated foetal monitoring
has found no significant alterations in foetal heart
rate, oxygen saturation in the cord blood, foetal
movement or uterine tone during the treatment9.
It is safe in all three trimesters of pregnancy. Where
indicated it is the treatment of choice as the brief
exposure to anaesthetics involved renders the risk of
congenital defects negligible, whereas the use of
antidepressants, antipsychotics and mood-stabilisers are
usually contraindicated because of the risk of
teratogenicity. ECT does not cause miscarriage - even
when given at term, and after rupture of the membranes,
ECT is not reported to precipitate labour.
My child/adolescent suffers from a specific
mental disorder, is it a safe procedure to use to
improve the condition?
Certainly, pending on the specific disorder. However,
the attitude of layman shaped by uninformed and
inexperienced mental health workers has led to
disfavouring the use of ECT in these age groups and
therefore the treatment method is totally underutilised.
It is a safe and effective treatment in children and
adolescents with intractable mental disorder, in
particular those with severe mood disorders, and leads
to complete recovery and good social integration in most
instances10.
Our mother is in her late seventies and frail.
We would like to improve the quality of her life, but
only want the best for her. Will ECT be harmful to her
or can it bring about an improvement in her mental
disorder?
Some of the most rewarding outcome with ECT occurs in
elderly, debilitated people whose primary mood or
psychotic disorder is expressed as dementia. There is
little risk reported in inadvertently treating a person
who has Alzheimer’s disease; indeed, ECT mitigates
depressive symptoms of patients with primary dementia
without worsening of cognitive functioning11.
I’m afraid to have ECT for it is said to
cause brain damage, is that true?
The important question of whether ECT causes structural
brain damage has been extensively researched.
Neuropathologic studies in animals, including cell
counts in regions thought to be at highest risk, fail to
find evidence of damage when treatments are given under
conditions that approximate standard clinical practice12.
Similar findings, i.e. no neuropathological changes,
were seen in humans. Lipman & co-workers (1985) recorded
no neuropathological changes in a patient who had
received 1,250 treatments over a 25-year period.
Studies of compared structural brain imaging findings
before and after ECT, found no ECT-induced changes on
CAT scans13 or MRIs14.
The most frequent complaint after ECT is that of memory
loss. People tend to forget that memory problems form
part of psychiatric illnesses per se, e.g. depression is
associated an acquisition deficit as revealed by tests
of immediate recall or recognition of item lists, and
successful treatment of depression with a course of ECT
is associated with improved test performance15.
Not surprisingly, one consistent finding is that the
greater the severity of depressive symptoms after ECT,
the greater the subjective complaints of impaired memory
and concentration16.
Objective memory testing has also shown normal memory
and cognitive functioning at long-term post-ECT
follow-up examination17. A few patients are
reported to have persistent patchy memory impairment
after ECT. Such memory loss might result from
con-current antidepressant medications18,
residual depression19, or progression of
pre-existing organic brain disease20.
The APA Task Force on ECT therefore
recommends that:
- All medicines, which may interfere with the
formation or recall of memory, be stopped during a
treatment series and,
- Memory functions be evaluated before and after a
treatment series.
Is the treatment as
such a terrifying experience?
Far from it, surveys done by Hughes et al in 1981,
Janicak et al in 1985, Freeman & Kendal in 1986,
Bernstein et al in 1998 and Kellner et al in 1999 on
patient attitudes about ECT after they’ve had a
treatment-series, found that:
- The majority felt that a visit to the dentist
was more distressing.
- The majority agreed with the statement ‘I wish I
had this years ago’.
- 85% stated that it would be their treatment of
choice in future if needed.
Anticipatory anxiety and
feelings of uncertainty are to some extent always
present when one is confronted by unfamiliar medical
procedures, but with the necessary explanations and
assu-rances however most these fears can be allayed. The
use of tranquillisers and sleeping tablets should be
avoided, as they reduce the efficacy of the treatment
method.
What work-up is needed before ECT?
ECT is always given whilst the recipient is under
induction anaesthesia and a muscle relaxant. Patients
who are to undergo this procedure require a complete
history and physical exami-nation. In addition, it is
advised that the following laboratory examinations are
routinely obtained for screening purposes:
- Full blood count including a diffe-rential white
cell count.
- Liver functions.
- Blood urea, urate and creatinine.
- Serum electrolytes, calcium and red blood cell
magnesium.
- Urinalysis.
- Pseudocholinesterase, where a personal or family
history of prolonged apnoea is obtained.
A written and witnessed consent
must be given by the patient (or in exceptional
conditions by the legal guardian) for every treatment.
The recipient is seen and examined by an anaesthetist
beforehand and an appropriate premedication prescribed.
Routine instructions regarding the treatment
consist of the following:
- Treatments will be given on Mon-days, Wednesdays
and Fridays or on Tuesdays, Thursdays and Saturdays,
starting at 06h30.
- Nothing by mouth after midnight prior to
treatment.
- Wherever possible and in consulta-tion with your
psychiatrist, discon-tinue all psychotropic
medicines.
- Remove all jewellery, hairspray, mousse,
make-up, facial cream and nail polish before
proceeding to the theatre. A greasy scalp or facial
skin hampers proper electrode contact, whereas nail
polish interferes with oximetry.
- Empty bladder immediately before entering of
treatment theatre.
What precisely
happens during such a treatment? What can you tell your
patients?
In the theatre your shoes are removed and you are helped
onto a special mobile-bed. A pulse-oximeter is clipped
onto the index finger. Electrodes are attached to the
chest to ensure constant ECG monitoring of the heart
throughout the treatment procedure. At the same time
special self-adhesive electrodes are placed on either
side of the forehead to measure and observe brain wave
activity through all phases of the treatment. The
oximeter measures the oxygen saturation of the tissues
continuously i.e. before, during and after application
of the stimulus. 100% oxygen is administered through a
mask.
The anaesthetist then injects intravenously a
short-acting anaesthetic, which induces sleep for plus
or minus 3 minutes.
At a set interval plus or minus 30 seconds thereafter a
muscle-relaxant is given and 100% oxygen is administered
by positive pressure at a rate of 20-30 respirations per
minute, and continued until return of spontaneous
breathing. Half a minute after the administration of the
muscle-relaxant, the stimulus is applied through two
electrodes to the scalp for a very brief one to two
second period. Stimulation of the brainstem and the
spreading of the activation process in the brain is
carefully monitored, timed and recorded throughout the
procedure.
When the person is able to respond to a request to open
his/her eyes, transfer to the recovery room takes place.
Here the administration of oxygen is conti-nued for
another few minutes. When wide-awake from the
anaesthetic, tea or coffee is enjoyed before the person
goes back to a general ward or as an outpatient to the
day clinic.
If you require more information on ECT, please contact
the author at (012) 993-2015.
References:
- Avery & Lubrano, 1979;Abrams, 1982; Siris &
co-workers, 1982; Rifkin, 1988; Sackeim &
co-workers, 1990; Bernstein & co-workers, 1998;
Olfson & co-workers, 1998; Kellner & co-workers,
1999.
- Benatov & co-workers, 1996; Chanpat-tana, 1997,
1998 & 1999; Christinson & co-workers, 1991; Ezion &
co-workers, 1990; Fink & Sackeim, 1996; Frankenburg
& co-workers, 1993; Friedel, 1986; Guvajarty, 1987;
Hoflich & co-workers, 1995; Klapheke,1991; Krueger &
Sackeim, 1995; Landy, 1991; Lohr, 1994; Meltzer,
1991 & 1992; Monroe, 1991; Sajatovic & co-worker,
1993 and Stephens & co-workers, 1993.
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Borchardt, 1990; Black & co-workers, 1985 & 1987;
Car & co-workers, 1983; Chou, 1991; Fink, 1993;
Goodwin & Jamison, 1990; Hill & co-workers, 1997;
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Milstein & co-workers, 1987; Mukherjee & Sackeim,
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Prudic & co-workers, 1990; Schnur & co-workers,
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Dudley & Williams, 1972; Fink, 1979 & 1999; Hafner &
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Lipowski, 1990; Mann & co-workers, 1986; Philbrick &
Rummans, 1994; Roberts, 1963; Stromgren, 1979 &
1997; Zwil & Pelchat, 1994.
- Kramer, 1985; Hermann & co-workers, 1995.
- Swartz & Inglis, 1990.
- Murray & co-workers, 1986.
- Alexopoulos & co-workers, 1984; Greenberg,
Mofson & Fink,1988.
- Wise & co-workers, 1984; Repke & Berger, 1984.
- Baker, 1995; Bertalogni & co-workers, 1990;
Mansheim, 1983; Ghaziuddin & co-workers, 1995; Moise
& Petrides, 1996; Fink, 1995; Paillere-Martinot &
co-workers, 1990; Sackeim & et al, 1987; Schneekloth
& co-workers,1993; Strober & Carlson ,1982; Thompson
& Blaine, 1987; Weiner & co-workers,1994.
- Demuth & Rand, 1980 ; Snow &Wells, 1981;
McAllister & co-workers, 1982; Dubovsky &
co-workers,1985; Price & co-workers, 1989.
- Dam & Dam, 1986; Meldrum, 1986; Weiner, 1984.
- Bergsholm & co-workers, 1989; Kendell & Pratt,
1983.
- Braffman & co-workers, 1988; Coffey &
co-workers, 1991 ; Mander & co-workers, 1987; Pande
& co-workers, 1990; Scott & co-workers,1990.
- Cronholm & Ottoson, 1963; Mattes & co-workers,
1990; Pettinati & co-workers, 1984; Sackeim & co
workers, 1993; Steif & co-workers, 1986.
- Frith & co-workers, 1983; Squire & Slater, 1983;
Squire, 1986.
- Squire & Chase, 1975; Weeks & co-workers, 1980;
Squire & co-workers, 1983; Abrams & Taylor, 1985;
Price & co-workers, 1982; Devenand &
co-workers,1991; Coffey & co-workers, 1994.
- Calev et al, 1989.
- Squire et al, 1979; Weeks et al, 1980.
- Coffey et al, 1991.
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