Psychophysiological investigation of false memory in amnesiac patients
2014
This thesis investigates psychophysiological characteristics of false memories in
two groups of people: healthy participants and amnesic brain injured patients with
Korsakoff syndrome (KS). KS patients present impairment of diencephalic structures in
the brain, mainly at mammillary bodies, thalamic nuclei, fornix and mammillothalamic
tract as consequence of thiamine deficit. This deficit is associated with dense
anterograde amnesia with general preservation of other cognitive abilities. The main
objective was to study how patients processed false memory compared to healthy agematched
controls.
To do it so, we produced several experiments. A first one was designed to validate
a new false memory task that offers a language-free alternative to the classic Deese-
Roediger-McDermot paradigm (DRM) along with some other improvements introduced
to bias false memory production. We tested this visual false memory task (VFMT) in a
sample of 20 healthy participants to study its validity as true and false memory
generator under event-related potential (ERP) conditions. Results indicated that classic
ERP old/new effect was present despite in showed a consistent central localization in
the scalp compared to what previous ERP experiments found. Moreover, we found that
true and false memory ERP signal appeared to be equivalent in localization but different
in voltage.
We aimed to study true and false memory in amnesic patients and compare their
performance with age-matched healthy controls. But before doing it we run an
experiment to adapt VFMT to amnesic characteristics of KS sample. We decreased the
amount of information to be studied engaging a shorter-delay testing time that may
overcome episodic and attentional difficulties in patients. Second version of the task,
i.e. VFMT2.0 was behaviourally applied to a sample of 10 KS patients to confirm that
this new version successfully produced enough amounts of true and false memories.
Neuropsychological assessment was also applied to KS patients to quantify and
characterize their cognitive impairment and brain damage.
Finally, ERP experiment was performed in KS patients and age-matched controls.
Respect to results from first version of VFMT, ERP differences appeared in healthy
participants. What behaviourally was reflected as an easier memory task, it also was
associated with ERP differences in localization of ERP activity in the scalp, implicating
more frontal-located electrodes for true memory processing compared to the central
distribution of ERP found at VFMT1.0. Moreover, under VFMT2.0 task, healthy
participants showed ERP differences when true and false memories were compared:
right-frontal electrodes for true and left-frontal for false memory processing on 500 to
1000ms time window. Regarding amnesic patients, brain activity associated to true and
false memory was equivalent and left-frontal sited all over the epoch. Main results
indicated that true memory processing showed different ERP characteristics when
patients were compared with controls despite their behavioural false memory rates were
equivalent. When false memory was analysed, differences between groups were also
found, mainly at early 300-500ms and later 1000 to 1500ms time windows.
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