Digging deep into depression
Think of a personal quality that is important to you, perhaps one
that defines you in some way. Now try to think of a specific memory, a
particular time and place that demonstrates this quality. Elaborate the
memory – sharpen the image. What colours, smells, feelings and textures
are associated with it?
One of the most extraordinary features of the human mind is our ability
to reconstruct past events in this way to provide a sense of ourselves
as continuous over time (Tulving, 2002). It’s a complex reconstructive
process, and Neisser (1967) compared autobiographical remembering to a
palaeontologist reconstructing dinosaurs: ‘Out of a few bone chips we
remember the past’ (p.285). Typically, autobiographical memories are of
particular events, comprise a narrative (who, what, when and where) and
include vivid associated imagery. However, people who suffer from
depression have difficulty retrieving specific memories – they build up
summarised schematics instead. To take Neisser’s palaeontology analogy,
their fossils tend not to spring to life to create
an image of a specific triceratops at a water-hole on a hot summer day,
instead preferring to create a schematised image of a dinosaur.
Cognitive theories of emotion propose that it is how we process the
inputs that become moment-to-moment experience that is all important.
Many people who suffer depression have not only experienced
considerable adversity, but their depression amplifies these
experiences through rehearsal and elaboration. They are less likely to
generate the specific autobiographical memories that are normally used
to solve problems, pursue goals, provide a self- and other-concept, and
regulate emotions. Instead, they are disengaged from the richness of
their pasts, both good and bad. They become a disembodied collection of
numbed feelings and depressive thinking. A first-person account from
someone who has suffered depression captures this well: ‘Under the
duvet, an internal ice age had set in. I had permafrost around my
heart’ (Lewis, 2002, p.1). Understanding autobiographical memory in
people like Sherry (see box) who suffer depression will enable us to
understand this paradoxical depressive process and improve our existing
evidence-based therapies for depression by providing specific ways of
helping people break these self-defeating patterns.
So how does modern research view autobiographical memory, and why should it differ in depression?
Box: Sherry’s autobiographical memories
Sherry, a 42-year-old married personnel manager, had suffered repeated
episodes of quite severe depression since she was 16. Her most recent
episode followed an argument with her brother about their parents’
finances.
Despite early family hardship, Sherry had done well in her career, was
in a stable marriage of 18 years and had two teenage children who were
doing well. But Sherry had come to see herself as fundamentally
‘flawed,’ and said ‘I have made terrible mistakes in the past’. Sherry
had learned to feel overly responsible for others’ problems and would
experience feelings of guilt and shame as she repeatedly rehearsed her
perceived failings.
When this was explored in therapy she described a specific incident
where she had not written a note of condolence to a friend whose father
had died. At the funeral, her friend ‘humiliated’ her in front of
others by rebuking her. Instead of seeing this as a result of the high
emotions of such a difficult occasion she saw it as absolute proof that
she was flawed. She tended to avoid challenging situations out of a
fear that she would make a mistake.
Sherry was prone to worry, and once locked in to a depressive mode of
thinking would feel quite severely disabled in her ability to be
proactive in either her work or her family. The negative self-focus
would disable her sense of competence and any number of slights,
disappointments, failures and grievances would intrude.
Theories of autobiographical memory
Contemporary theories of autobiographical memory have a number of
main propositions in common (for a very readable review, see Schacter,
1996).
Firstly, the self-concept and autobiographical memory are in constant
dynamic interplay. That is to say, the person’s working goals influence
encoding, storage and retrieval of autobiographical memory. A classic
illustration of this is Howard Dean’s detailed testimony of
conversations he had with US President Richard Nixon during the
Watergate scandal. When the tapes of those conversations were released
it became clear that the tapes were at odds with Dean’s testimony
because Dean’s memory was shaped by his personal goals (Neisser, 1982).
He tended to overstate his own role in the scandal and cast it in a
more positive light than the tapes. This type of memory reconstruction
is not an aberrant process, but a normal feature of autobiographical
memory retrieval.
Secondly, autobiographical memory is broadly hierarchically organised into
at least three levels (Conway & Pleydell-Pearce, 2000): lifetime
episodes (e.g. ‘when I was at primary school’); categories of
summarised events (e.g. ‘attending funerals’) and event-specific
knowledge (e.g. ‘the day my friend humiliated me at her father’s
funeral’). Retrieval of a specific autobiographical memory involves
using higher levels of the hierarchy to reconstruct the sensory,
perceptual and semantic information stored as event specific knowledge.
Finally, retrieval can be either strategic or involuntary. Strategic
retrieval deploys considerable cognitive resources as memories are
reconstructed in relation to current goals, as relevant information is
activated and irrelevant information is inhibited. Involuntary memories
are bottom-up, cued by external or internal cues (e.g. a sensory cue
like a smell); include intrusive traumatic memories; require few
cognitive resources; and override the content of current awareness. In
strategic retrieval this process takes place under the auspices of a
supervisory executive system, while involuntary memories are activated
through a more powerfully automatic and associative process.
Memory in depression
While studying the idea that people diagnosed with depression
preferentially access negative memories, Mark Williams discovered that
people who suffer depression often have difficulty producing specific
memories (Williams, 1996). They will recall ‘arguments with friends’,
rather than ‘the argument I had with my best friend last Friday’. A
recent meta-analysis of 14 studies suggests that this is a robust
finding (van Vreeswijk & de Wilde, 2004).
The problem appears to be primarily specific to people who suffer mood
difficulties, although overgeneral memory functioning has also been
observed in a variety of samples exposed to trauma, such as accidents,
combat and childhood abuse (Hermans et al., 2004; Kuyken & Brewin,
1995). It is noteworthy that in clinical samples the presence of
negative psychological reactions to trauma – most notably
post-traumatic stress symptoms (intrusions and avoidance) – are
associated with greater overgeneral memory retrieval. Tentative
evidence points to overgeneral memory as a trait-like phenomenon that
persists between depressive episodes (e.g. Mackinger et al., 2000).
This trait is associated with impaired social problem solving, impaired
ability to use memories to regulate feelings, and poor outcomes; but it
can be modified through psychological interventions, such as
mindfulness-based cognitive therapy (Williams et al., 2000).
Explanations
Several explanations for the overgeneralised autobiographical memory effect in depression have been proposed.
I have tried to summarise the main current accounts into four broad hypotheses.
The limited cognitive resource hypothesis This proposes that
depression and PTSD are typically characterised by depleted cognitive
resources, especially in executive functioning that ‘supervises’ the
retrieval process (Conway & Pleydell-Pearce, 2000). Depression is
associated with a range of cognitive deficits in executive functioning.
Moreover, people who have experienced trauma and experience ongoing
PTSD symptoms are likely to be preoccupied with inhibiting these
upsetting intrusive images and thoughts. This depletion of cognitive
resources in depression could limit resources required for strategic
autobiographical memory retrieval, because the highly effortful final
stage of retrieval – pulling together sensory and perceptual
information into a coherent specific memory – requires too many
resources.
For Sherry, her mood difficulties tended to be associated with
significant levels of generalised anxiety; she would become preoccupied
with a stream of ruminative thoughts and images. The rumination took up
cognitive resources, and undermined problem solving and genuine
processing of emotions.
This hypothesis accounts for the (inconsistent) findings that trauma
symptoms (intrusive thoughts and memories) exacerbate overgeneral
memory retrieval. It is also consistent with the finding that
overgeneral memory retrieval is seen in groups where executive function
is impaired (some older adults and following frontal brain disease; see
Levine, 2004). However, not all studies have shown a relationship
between executive functioning and overgeneral memory in people
diagnosed with depression.
The availability heuristic hypothesis This stipulates that
current frames of reference make related information more available and
will therefore make retrieval of related information more likely
(Kahneman, 2003). As outlined above, the current frame of reference is
likely to be active personal goals linked to the self-concept. In
depression, general themes created in depressive thinking (e.g. the
self as defective or unlovable) prime related overgeneral memories,
both in terms of level of representation (overgeneralised) and content
(congruent with depressive schema).
For example, in our case example Sherry tended to withdraw from life
when she noticed the first signs of depression because she was
convinced that ‘nothing helps’. This primed overgeneralised summary
memories like ‘None of the things I have tried has worked’. Only with
considerable support would she retrieve a specific memory at odds with
the overgeneralised level of representation and the goal of finding
stable and global evidence of helplessness, like ‘Last Saturday I
visited my dad and we went out for a long walk and I seemed to forget
all about my troubles’.
Specific memories may even be actively excluded at a late stage of
memory retrieval because they are inconsistent with the overgeneralised
current working goal. In many ways overgeneral memories (e.g. ‘Nothing
I have tried works’) are like fuel to the fire of depressive thinking
(e.g. ‘I am flawed’). This explanation is consistent with several
recent experimental studies showing that when people who are depressed
change from an evaluative-conceptual to a more experiential mode of
processing, they are able to generate more specific memories (Watkins
& Teasdale, 2001). It also helps explain why the phenomenon is
observable for both positively and negatively valenced emotional
memories and both trivial and important memories.
The cognitive avoidance hypothesis This hypothesis (Williams,
1996) suggests that during retrieval the search process from semantic
associates to categorical summary memories to specific memories locks
at the overgeneral categorical level
as a form of avoidance of the emotion associated with event-specific
knowledge. It is argued that this strategy is over-learned in the
context of early adversity because avoiding upsetting emotion is
negatively reinforcing. At the reconstructive stage, when summary
information (e.g. ‘mistakes at work’) comes into awareness, the emotion
associated with sensory and perceptual event-specific information (e.g.
shame) signals the executive system to inhibit event-specific knowledge
and truncate the memory retrieval process.
This hypothesis is consistent with the finding that overgeneral memory
is observed among people with a history of trauma and subsequent
intrusive memories. Essentially, people who experience depression that
is characterised by high levels of PTSD symptoms learn to collapse
their autobiographical memories into manageable pockets of summarised
information (in Sherry’s case ‘I have made terrible mistakes’). This
hypothesis is also consistent with findings that PTSD symptoms are
common in depression (Kuyken & Brewin, 1994) and that overgeneral
memory is exacerbated by the presence of PTSD symptoms (Kuyken &
Brewin, 1995). More recently, prospective studies examining the
interaction of stress and overgeneral memory retrieval style have shown
that overgeneral memory might serve to protect the person in the short
term (Raes et al., 2003) but in the medium term is associated with the
development of depressive symptoms (Gibbs & Rude, 2004).
The functional brain impairment hypothesis This argues that
prolonged stress during crucial developmental periods may limit the
functional capacity of the brain to perform complex modular functions.
Prolonged stress is common
in the history of people with recurrent depression, especially in the childhood
and adolescence of early onset recurrent depression. There is
(conflicting) evidence that prolonged stress is associated with reduced
hippocampal volume, a structure implicated in strategic memory
retrieval (Cordon et al., 2004). This explanation is consistent with
the relative stability of the phenomenon and its pervasiveness across
positive and negative memories and findings of overgeneral memory in
people with brain injury, but is less easy to reconcile with findings
showing that it can be modified through brief experimental
manipulations. In a recent study, administration of cortisol was
associated with reductions in specificity of autobiographical memory,
suggesting support for a functional brain impairment hypothesis (Buss
et al., 2004).
These four hypotheses are not mutually exclusive, indeed they are
likely to be self-reinforcing: rumination might lead to reduced
resources and overgeneral memory; prolonged early adversity could lead
to elevated levels of cortisol, structural brain changes and
consequently to fewer cognitive resources for autobiographical memory
retrieval. Arguably, the functional brain impairment, cognitive
avoidance hypothesis and the limited cognitive resource hypothesis are
all restatements of the same basic idea – namely, functionally impaired
higher-order cognitive processing. This position is consistent with the
weak support currently available for each hypothesis. It is premature
to attempt a theoretical synthesis of mood and memory until these
hypotheses are systematically examined.
Research challenges
The first research challenge facing this area is to address the
explanations outlined above; unpacking in which circumstances and at
which level each hypothesis confers explanatory power. Experimental
designs that can manipulate schema accessibility, available executive
resources and emotionality will likely distinguish the accessibility,
cognitive avoidance and breakdown of inhibitory control hypotheses.
A second research challenge is the neuroscience of encoding, storage
and retrieval of autobiographical memory. Autobiographical memory
almost certainly emerges from the coordination of multiple cortical and
subcortical brain systems. It is exciting to consider the possibility
of unpacking the pathways involved in autobiographical memory
associated with different brain structures, and the way in which
depression and trauma might affect these pathways (e.g. Conway et al.,
2001).
We know little about the broader characteristics of autobiographical
memories among people who suffer depression. What is the qualitative
content of autobiographical memories on dimensions such as affectivity,
personal saliency, field versus observer perspective, recency,
coherence…? There is good reason to suppose that someone who engages in
extensive overgeneralised depressive memories would become
unable to differentiate what was actually experienced from what was
thought about the experience, a well-researched autobiographical
phenomenon known as source-monitoring errors (Johnson et al., 1993).
Dirk Hermans, Filip Raes and colleagues have started to examine how
overgeneral memory is related to rumination and source monitoring in
depression and these data are likely to move our understanding on
substantially.
A recent study suggests that when compared with never-depressed
controls, the autobiographical memories of depressed adolescents show
an exacerbated recency effect and are more likely to be recalled from
an observer perspective (e.g. seeing the memory from a bird’s eye
perspective), which suggests differences in the scope and type of
memories available to depressed adolescents (Kuyken & Howell,
2006). Phenomena like source monitoring, recency effects, field versus
observer perspective in autobiographical memory are only just beginning
to be studied in people diagnosed with depression. Discovering whether
the extensive literature on ‘normal’ autobiographical memory is
replicable in people who are vulnerable to depression will
substantially develop our understanding of depression.
Finally, the established functions of autobiographical memory in the
general population need extending to depression, drawing on the
parallel literatures in cognitive and social psychology. In what ways
does autobiographical memory support goal-directed behaviour and the
elaboration of the self-concept in people who suffer depression?
Towards practice
Together, these lines of research will enable a theoretical
synthesis of mood and memory. From a clinical perspective, the pressing
question is how can we enhance existing effective psychological
treatments by explicitly developing protocols for addressing the
autobiographical memory paradox? It is likely that overgeneralised
memory is functional in some contexts and dysfunctional in others. How
can we help people process emotional experiences and use their
autobiographical experiences (good and bad) in a way that enhances
their resilience? Returning to our case example of Sherry, how can she
process her ‘humiliating’ memory of her friend’s criticism, and how can
she bring to mind memories to help her regulate her emotions and
enhance her self-esteem when her ‘self-as-flawed’ mode is activated? A
participant in a recent study conducted in the Mood Disorders Centre in
Exeter said of her experience of cognitive behaviour therapy: ‘I was
expecting a lot more talking, less of, you know, what exactly did
happen at this point and how did you feel …um…it was very precise
…which is what I needed really rather than having this glob of
experiences floating around in my head and knowing that they made me
feel bad. I needed (my thinking) to be pinned down.’
Digging deep
Being readily able to bring to mind specific, vivid and well
elaborated memories confers many adaptive advantages, but people who
suffer depression preferentially retrieve overgeneral memories.
Overgeneral memory retrieval is very likely to be implicated in
difficulties with problem solving and in the course of depression.
Overgeneral memory may be a function of the accessibility of
overgeneralised information in depressive frames of mind, an
over-learned cognitive avoidance strategy, depleted general cognitive
resources required in retrieval or an artefact of brain impairments. We
do not yet have a compelling theoretical synthesis that can explain
this intriguing, paradoxical and important phenomenon in depression.
But we will not move closer to understanding autobiographical memory
0in depression if we hug intellectual shorelines. Genuine increases in
understanding require the synthesis of cognitive, clinical,
developmental, neuroscience and social psychological knowledge and
research. Similarly, developing our interventions for depression
requires us to begin thoughtfully and systematically to apply what we
know about depression to our therapeutic approaches to intervention.
- Willem Kuyken is at the Mood Disorders Centre at the University of Exeter. E-mail: [email protected].
Weblinks
Depression Alliance: www.depressionalliance.org
Mood Disorders Centre: www.centres.ex.ac.uk/mood
Discuss and debate
What are the possible explanations for the overgeneral memory phenomenon in depression?
What functions (if any) does overgeneralised autobiographical memory serve?
What sorts of therapeutic interventions might help someone to be flexible in retrieving specific and categoric memories?
What impact might trauma have on autobiographical memory retrieval?
Have your say on these or other issues this article raises. E-mail
Letters on [email protected] or contribute to our forum via www.thepsychologist.org.uk.
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