"Paradigms and brain imaging 
technologies art becoming progressively 

more exacting, allowing cognitive 
scientists to investigate the ... neural 
circuitry responsible for abstract and 

uniquely human traits." 



R E M I N I S C I N G A N D D A Y D R E A M I N G 

Investigating the Similarities Between Episodic Memory 

Recall and Imagination 

K Y L E F I S C H E R 

T H E P O W E R O F I M A G I N A T I O N H A S L O N G B E E N T O U T E D A S A D I S T I N C T I V E P R O P E R T Y 

O F H U M A N C O G N I T I O N A N D R E M A I N S A H E A T E D T O P I C A M O N G S T P H I L O S O P H E R S , 

S C I E N T I S T S , A N D D A Y D R E A M E R S A L I K E . D E S P I T E P L A Y I N G A C R I T I C A L R O L E I N T H E 

M A J O R I T Y O F H U M A N I T Y ' S F I N E S T A C H I E V E M E N T S , L I T T L E IS K N O W N A B O U T H O W 

T H I S F A C U L T Y A C T U A L L Y W O R K S . R E C E N T F I N D I N G S F R O M L E S I O N P A T I E N T S P O I N T 

T O T H E I N V O L V E M E N T O F T H E H I P P O C A M P U S IN I M A G I N I N G N E W S C E N A R I O S . T H E 

H I P P O C A M P U S IS H I S T O R I C A L L Y A S S O C I A T E D W I T H L O N G - T E R M M E M O R Y 

C O N S O L I D A T I O N , A N D M E M O R Y M O D E L S A R I S I N G F R O M N E W F I N D I N G S IN T H E 

M O L E C U L A R P A T H W A Y S O F M E M O R Y A L L O W F O R A M O R E F L U I D T R A N S I T I O N B E T W E E N 

I M A G I N A T I O N A N D M E M O R Y . E L I Z A B E T H L O F T U S ' F A M O U S S T U D I E S O F F A L S E 

E P I S O D I C M E M O R Y R E C O V E R Y F U R T H E R D E M O N S T R A T E O V E R L A P B E T W E E N I M A G I N E D 

A N D R E C A L L E D E V E N T S . F I N A L L Y , A N F M R I S T U D Y I S P R O P O S E D T O C O M P A R E B R A I N 

A C T I V I T Y D U R I N G B O T H E P I S O D I C M E M O R Y R E C A L L A N D T A S K S T H A T R E Q U I R E 

I M A G I N A T I O N IN O R D E R T O P I N P O I N T R E G I O N S F O R F U R T H E R I N V E S T I G A T I O N . 



As the field of neuroscience expands, it is increasingly en-

tering uncharted territory; the pieces of human experience 

that were once major arguments for Cartesian dualism, in-

cluding morality, foresight, and theory of mind, are quickly 

finding neural homes. Paradigms and brain imaging tech-

nologies are becoming progressively more exacting, allow-

ing cognitive scientists to investigate the brain regions and 

neural circuitry responsible for abstract and uniquely 

human traits. One of these traits is imagination, the ability 

to produce vividly detailed episodic events. Recent studies 

of hippocampally-lesioned patients have shown that these 

injuries result in the inability to formulate new imaginative 

experiences,1 suggesting that these regions, classically 

linked with memory, are also necessary for imagination. 

New findings i n memory research have offered a modified 

memory model 1 1 suggesting a fluid continuum between 

real episodic memories and episodic imaginative experi-

ences. The error-prone nature of episodic memories as 

evidenced by false memory experiments 1 1 1 supports the 

theory of a synonymous relationship between what is 

currently conceived as episodic memory and imagination. 

I n light of this evidence, we wi l l discuss a possible experi-

mental paradigm that wi l l investigate similarities i n brain 

activity induced by episodic memory recall and the produc-

tion of an imaginative narrative. 

IMAGIN ING A DRAGON IS A PROCESS WH ICH LIKELY OCCURS 
IN T H E H IPPOCAMPUS. 

Episodic memory is a uniquely human trait that expresses 

information i n a detailed narrative fashion, coding for who, 

what, where, when, and why . l v v When conventional speech 

refers to 'memories', it is most likely referring to episodic 

memories. For example, recall a childhood memory, per-

haps your first baseball game. You may remember step-

ping up to home plate, hearing your mom and dad cheer, 

and striking out in humiliation. Perhaps you may remem-

ber the smell of the grass, the warm summer light, or the 

taste of the snacks back in the dug out. Now imagine a com-

pletely fanciful event, perhaps a dragon attacking a ship full 

of Vikings. Again, you can hear the sea, taste the salt water, 

and feel the heat of the dragon's breath. As a final exercise, 

try integrating the two; while stepping up to the plate in 

your first baseball game, have a dragon stroll out into left 

field. 

Ridiculous, perhaps, but this brief exercise illustrates that 

as far as the nature of the mental experience is concerned, 

imagination and episodic memory seem, i f only anecdo-

tally, identical. Although some nonhuman animals have 

displayed episodic-like memories,V 1 Homo sapiens are the 

only known species to possess this ability.V 1 1 As one might 

surmise from the previous exercise, classical false memory 

studies have been able to modify, falsify, and even produce 

new fictitious memories of fantastic proportions. One of 

the more classical studies, by Loftus, v m asked participants 

to recall a series of childhood memories that were given to 

the researchers by the participants' parents. During these 

sessions, the investigators would also ask the participants 

about having been lost i n the mall as a child, which the par-

ents of the participants confirmed had never happened to 

their children. Nonetheless the participants recalled confi-

dently the fictitious event, even creating precise details. 1 X 

The suggested nature of episodic memory supports the 

fluid model, which integrates imagination and episodic 

memory, but an understanding of the underlying mecha-

nism of memory production is necessary to further investi-

gate this theory. Memory is comprised of past events, but 

the function of memory is strictly future-based. A n 

E L E M E N T S 
F A L L 08 



ever-changing environment behooves an organism to 

record responses in the chance that similar events occur in 

the future. In humans, the seat of memory is the hip-

pocampus, a bilateral pair of horns that curl in the subcor-

tical region of the brain, ending with the amygdala.x As 

lesion patient studies have shown, loss of the hippocampus 

results in profound short-term memory loss, as well as a 

deficit in the ability to create new long-term memories.X 1 

The findings from these and other memory studies have 

led to the proposal of a memory model in which short-term 

memories, lasting from a few seconds to a few hours, are 

recorded i n the hippocampus and are later consolidated to 

the cortex as long-term memories, where they can remain 

for a l i fet ime. X 1 1 ' X 1 U 

synapses. Subsequent co-activation of these two synapses 

further increases A M PA numbers unti l these neurons fire 

swiftly with the smallest synaptic activity.™ 

Behaviorally, the Pavlovian response is observed; if, for ex-

ample, a rat hears the tone that is followed by an electric 

shock, it wi l l quickly behave in response to the tone as i f it 

were being shocked. The activation provided by the 

neurons responding to "tone", after a repeated exposure to 

the tone-shock pairing that induced long-term potentia-

tion, is enough to elicit a shock response without co-stimu-

lation. The manner in which the hippocampus codes for 

the information that comprises such memories remains 

unknown. However, injection of a protein synthesis in-

hibitor such as anisomycin during training sessions blocks 

"Memory is comprised of past events, but the function of 
memory is strictly future-based. An ever-changing 

environment behooves an organism to record responses in 
the chance that similar events occur in the future." 

Recent neurobiological research has challenged, or at least 

modified, this long-standing memory dogma. At the neu-

ral level, memory encoding begins with a process called 

long-term potentiation, in which the co-stimulation of a 

neuron by two separate neurons at the same time molecu-

larly increases the efficiency by which that neuron can later 

be activated under a similar circumstance. x i v This coinci-

dental strengthening is often referred to as Hebb's Law, ex-

pressed as "neurons that fire together, wire together." x v Co-

stimulation leads to molecular changes facilitated by 

magnesium ions and voltage-gated NMDA channels, 

which respond to the excitatory neurotransmitter gluta-

mate, causing an influx of calcium ions and, after a short 

metabolic pathway, protein synthesis that produces A M PA 

receptors that are inserted specifically in the activated 

the production of A M PA receptors, long-term potentiation, 

and subsequent memory of the association between tone 

and shock. x v n Surprisingly, recent findings from Nader x v m 

show that i f a protein synthesis inhibitor is injected when 

the learned behavior is recalled at a later date, the presenta-

tion of a tone long after the inhibitor has worn off wi l l elicit 

very little behavioral response. In effect, the memory is 

erased when it is recalled in the presence of a protein syn-

thesis inhibitor. Nader has proposed that instead of a short-

term and long-term memory system, memories are rather 

in a labile, active state or an inactive, consolidated state, and 

the process of consolidation and reconsolidation are 

practically identical. x l x 

R E M I N I S C I N G A N D D A Y D R E A M I N G 



The study has caused much excitement and controversy in 

the psychology field due to its potential as a therapy to erase 

or dull traumatic memories, but it also raises questions as 

to the evolutionary selection of such a memory system. 

According to the active/inactive state memory model, every 

time a memory is recalled it is liable to be disrupted. The 

nature of this model seems very unstable, especially when 

one considers that those memories that are recalled the 

most are probably the most important. However the sys-

tem seems highly evolutionarily conserved, with the same 

effects of protein synthesis inhibitors dulling or erasing be-

havioral memory responses i n rats, chickens, and crabs. x x 

The positive attribute of this system is that the labile state 

achieved i n recalling a memory allows it to be brought back 

to the mental drawing board, where it is open to editing. 

Thus an individual can continually add to several memory 

scripts; a memory for "tone = shock = freeze" recalled to a 

labile state can easily have another stimulus added to it , in-

creasing the efficiency of behavioral learning, a trait that 

could dramatically increase the survival of an individual. 

For example, a rat that remembers "tone = freeze" wi l l very 

quickly learn "light flash = freeze" when a light flash is 

placed directly before the tone/shock training. In humans, 

lesion patients without the facility of a hippocampus are 

unable to arrange remembered events in a correct order, 

supporting the idea of the hippocampus as the region 

responsible for the assembly of a memory narrative.™ 

It could also be possible that the only memories prone to 

error in an active/inactive memory model are episodic 

memories. Memories are split into two categories: declar-

ative and nondeclarative. Declarative memories are further 

split into episodic and semantic memories, the latter of 

which deals with facts and certain language skills. 

Nondeclarative, or implicit memories, record procedural 

memory, perceptual representation systems, classical con-

ditioning, and nonassociative learning. x x i i Few non-

human animals display semantic memory capabilities, but 

the majority of cognoscente species have nondeclarative 

faculties.X X U 1 I n an active/inactive model of memory, the 

implicit information coded by these types of behavior, like 

a tone beep or the motions used for riding a bike, are un-

likely to be falsely modified as the only equivalent data that 

can replace the coded information is derived from environ-

mental stimuli. As we have seen from false memory 

studies, episodic memory seems to have the unique charac-

teristic of being highly susceptible to thought-provoked re-

consolidation error. 

Interestingly, it wasn't unti l 2007 that hippocampus lesion 

patients were tested for their ability to create mental images 

in response to a verbal prompt . x x i v Episodic memory pro-

duction is practically nonexistent i n these individuals, and 

i f imagination is synonymous with episodic memory recall, 

one would expect to see retarded imaginative processes. 

Compared to control individuals of the same age and IQ, 

the responses of the amnesic patients were severely frag-

mented, labored, and non-descriptive, leading the research 

team to conclude that imagining new events was impossi-

ble for hippocampally-lesioned patients. 

To decisively test whether episodic memory and episodic 

imagery are the same wil l require a comparative study of 

brain activation during both tasks. Before the experiment 

begins, participants wi l l be asked to send their parents a 

short questionnaire about events from their child's past. 

While lying i n a function Magnetic Resonance Imaging 

(fMRI) machine, the participants wi l l be prompted with ei-

ther one of their childhood memories or an event that never 

occurred. They wil l then be asked to recall the event and 

mentally relive the experience, regardless of its validity. I f 

the prompt is of a familiar event, the participant wi l l be 

asked to recall the specific memory. I f the prompt doesn't 

ring a bell i n the mind of the participant, they wi l l be asked 

to imagine the event as i f it had truly occurred. For the com-

fort of the participant, the parents wi l l be asked for only pos-

itive events. The participants wi l l be told to be as vivid as 

possible in recalling the memory, and upon finishing the 

session, lasting only a few minutes, they wil l need to de-

scribe their mental responses. The participants wi l l also be 

asked to acknowledge which scenarios they recalled and 

E L E M E N T S : : F A L L 08 



E N C O D I N G O F E P I S O D I C M E M O R I E S A C T I V A T E S N U M E R O U S PARTS O F T H E BRA I N,AS S E E N H E R E IN T H I S S E R I E S O F MR I S . 



which they imagined occurring, and brain activities be-

tween these two groups wi l l be compared. 

Past positron emission tomography (PET) studies have 

found different activations during the encoding and re-

trieval of episodic memories, x x v often termed 'hemispheric 

encoding-retrieval asymmetry > X X V 1. Encoding activity has 

been shown to activate left prefrontal cortex and right hip-

pocampal regions in the majority of individuals. Retrieval 

has been shown to activate only the left prefrontal cortex, 

and i f imagining and episodic memory retrieval were of the 

same nature, one would expect similar activations. 

Despite these illuminating 

results, the majority of the 

paradigms that produced 

these patterns of activation 

used single still images as 

cues, which are poor real 

world examples of episodic 

memory. The paradigm 

proposed here uses real 

autobiographical episodes 

rather than single images. 

Also, retrieval required ac-

knowledging familiarity 

when new and old images 

were presented to partici-

pants, while this proposed 

experiment requires a mental recount of each episodic 

event. Although the cues used in these past experiments 

would qualify in content as episodic memories, they are 

poor examples of the powerfully expressive nature of 

human episodic memory. That being said, regions of acti-

vation could vary widely from these previous results in lat-

eralization, but wi l l most likely still occur within the left 

prefrontal cortex, hippocampus, and anterior cingulate 
gyrus xxvii>xxviii 

Other interesting considerations could be applied to fur-

ther experiments; i f imagination and episodic memory uti-

T H E BRAIN U N D E R G O E S A COMPLEX PROCESS WHEN 
CH ILDREN USE THE IR I M AG I N AT IONS. 

lize the same brain regions to function, does forcing one 

function hinder the production of the other? For instance, 

would accuracy in passive memory tasks decrease while a 

participant is daydreaming, or vice versa, while hippocam-

pus activity remains the same? What roles do attention 

areas play in switching classically episodic regions from 

recording real life to reliving fictions? x x l x Do these areas 

play a role in the dream production of REM sleep? The 

frontal lobes are known to play a large role in global brain 

activities, including working memory, novel object recogni-

tion, and planning for the future.30™*** 1 I f the frontal lobes 

are the region associated with Baddeley's central execu-

tive, 5 0™ 1 is episodic memory 

one of the processes of a 

visuospatial sketchpad, the 

other being creative 

imagery? What role would 

the switch between the 

imagined and the real play 

i n a schizophrenic's 

notorious misinterpreta-

tions of imagined events? 

Imagination is one of the 

cognitive abilities that, unt i l 

recently, most cognitive 

neuroscientists would not 

touch with a long pole; it re-

minds one too much of the 

ambiguously defined subsets of the dualist mind. With in-

creased understanding of our species cognitive abilities, re-

search scientists are quickly closing i n on subjects once left 

only to the discussions of philosophers. Some of this re-

search raises questions about the way we perceive imagina-

tive processes. Findings describing the neural basis for 

memory reconsolidation allow for a more fluid memory 

model that explains the errors notorious to episodic mem-

ory as seen in false memory studies. Hippocampus lesion 

amnesiacs not only display a loss i n short-term memory 

and long-term memory production, but also the inability to 

create episodic narratives. As abstract as it may sound at 

E L E M E N T S 
F A L L 08 



first, imagination is a concise cognitive ability that may be 

synonymous with episodic memory recall. Understanding 

the mechanism underlying the similarities and differences 

between these two cognitive abilities could have implica-

tions in attention theories, REM dream theory, and mem-

ory models, as well as our perception of reality. 

E N D N O T E S 
i . Hassabis (2007) 
i i . Nader (2003) 
i i i . Loftus (1997) 
iv. Sudderdorf (2007) 
v. Gazzaniga (2002) 
vi . Gazzaniga (2002) 
v i i . Sudderdorf (2007) 
v i i i . Loftus (1997) 
ix. Loftus (1997) 
x. Gazzaniga (2002) 
xi . Gazzaniga (2002) 
xi i . Nader (2003) 
x i i i . Gazzaniga (2002) 
xiv. Frey & Morris (1997) 
xv. Gazzaniga (2002) 
xvi. Frey & Morris (1997) 
xvii. Frey & Morris (1997) 
xvii i . Nader,(200o) 
xix. Nader (2003) 
xx. Nader (2003) 
xxi. Shimamura (1990) 
xxii. Gazzaniga (2002) 
xxiii . Tulving (2005) 
xxiv. Hassabis (2007) 
xxv. Haxby (1996) 
xxvi. Gazzaniga (2002) 
xxvii. Cabeza (2003) 
xxviii. Gazzaniga (2002) 
xxix. Cabeza (2003) 
xxx. Knight (1996) 
xxxi. Henson (1999) 
xxxii. Baddeley (1996) 

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R E M I N I S C I N G A N D D A Y D R E A M I N G