Psy 120.3 Lecture October 29 2025: Memory
For this lecture, we will start with molecular biology, and then move to classic memory theory and testing.
Long Term Potentiation
Let's look at a video of this process first:
https://www.youtube.com/watch?v=-mHgPfXHzJE
What you need to know for the next exam:
LTP is a process by which synaptic connections between neurons become stronger with frequent activation. LTP is thought to be a way in which the brain changes in response to experience, and thus may be an mechanism underlying learning and memory.
There are a number of ways in which LTP can occur. The best-known mechanism involves a glutamate receptor known as the NMDA receptor. In NMDA-receptor dependent LTP, glutamate release first activates a subtype of glutamate receptor known as the AMPA receptor. NMDA receptors are found nearby these AMPA receptors, but are not activated by low levels of glutamate release because the ion channel of an NMDA receptor is blocked by a magnesium ion. If frequent action potentials cause greater stimulation of AMPA receptors, however, this will cause the postsynaptic neuron to depolarize, which eventually causes the voltage-dependent magnesium blockage of the NMDA receptor to be removed, allowing calcium ions to flow in through the NMDA receptor. This influx of calcium initiates cellular mechanisms that cause more AMPA receptors to be inserted into the neuron’s membrane. The new AMPA receptors are also more responsive to glutamate, and allow more positively charged ions to enter the cell when activated. Now, the postsynaptic cell is more sensitive to glutamate because it has more receptors to respond to it.
LTP actually restructures the post-synaptic neuron and that is considered to be the basis of learning.
Long-term potentiation (LTP) in psychology refers to . It is a key biological mechanism for synaptic plasticity, which is the ability of the brain to change its structure and function. This process is widely considered to be the cellular basis for learning and memory because it enhances signal transmission between neurons, making communication and the storage of information more efficient.
Classical and Historical Research
Memory is the ability to store and retrieve information over time.
Researchers are discovering differences in the structure of several brain regions
known to be involved in memory in individuals who possess superior
autobiographical memory, such as Jill Price (LaPorte et al., 2012).
Encoding is the process of transforming what we perceive, think, or feel into an
enduring memory.
Storage is the process of maintaining information in memory over time.
Retrieval is the process of bringing to mind information that has been previously
encoded and stored.
Memories are made by combining information we already have in our brains with
new information that comes in through our senses.
Memories are dynamically constructed, not recorded.
Semantic encoding is the process of relating new information in a meaningful to
knowledge that is already stored in memory. (Brown & Craik, 2000)
Craik and Tulving (1975) presented participants with a series of words and asked
them to make one of three types of judgments: (1) semantic [meaning]; (20 rhyme
[sound]; (3) CASE [visual appearance, such as uppercase vs. lowercase].
The participants who made semantic judgments had much better memory for the
words than did participants who thought about how the word sounded or looked.
Semantic encoding is uniquely associated with increased activity in the lower left
part of the frontal lobe and the inner left part of the temporal lobe. The amount of
activity in each of these regions during encoding is directly related to whether
people later remember an item. The more activity there is in these areas, the more
likely the person will remember the information.
Visual memory is the process of storing new information by converting it into mental pictures.
Schnorr & Atkinson (1969) reported that in one experiment, participants who studied lists of words
by creating visual images of them recalled twice as many words as participants who just
mentally repeated the words. But, there is much more to 'mentally repeating' than first appears:
subvocalization.
Standing & Curtis (1989) reported that two experiments were performed to determine how
accurately the immediate memory span may be predicted from the subject's subvocalization
rate, as compared with other subject and stimulus variables. They concluded that the span
appears more closely related to subjects' internal speech rate than to other cognitive functions.
Visual encoding does the same thing that semantic encoding does: when you create a visual
image, you related to information already in memory.
 When you use visual encoding, you create two placeholders in memory: one visual, one semantic.
Visual memory encoding activates regions in the occipital lobe, which suggest that the visual
system is engaged in forming visual memories based on mental images.
For our purposes, let's use a more systems approach:
Visual memory involves multiple brain regions, with occipital lobe as the primary visual processing hub and the hippocampus and temporal lobe playing crucial roles in storing and retrieving the information. While the occipital lobe processes visual information initially, the hippocampus is vital for consolidating and storing memories, while the temporal lobe is involved in short-term memory, recognition, and processing sensory information. The frontal lobe is also involved in recalling visual information.Â
Dresler et al. (2017) reports neuroimaging evidence shows that training ordinary people to use
visual imagery encoding procedures produces neural changes in visual and memory networks
that support enhanced memory performance.
Researchers recently tested a smartphone app that provided training in using visual imagery to encode new information for adults ranging in age from 20 to 90 years (Sandberg et al., 2021). They found that training improved memory performance on a task that required encoding and recalling the order of a sequence of pictures in all but the oldest of adults.
Organizational encoding is the process of categorizing information according to
the relationships among a series of items. People can improve recall of individual
items by organizing them into multiple-level categories, called hierarchies.
Organizational encoding activates the upper surface of the left frontal lobe; different
types of encoding strategies appear to rely on different areas of brain activation.
Survival Encoding
Encoding by survival-related information is based on evolutionary psychology;
the features of an organism that help it to survive and reproduce are more likely
than other features to be passed on to subsequent generations. Our memory
systems should be built n a way that allows us to remember especially well
encoded information that is relevant to our survival.
Naime, Thompson & Pandeirada, 2007 showed that experimental participants
recalled more words after a survival-encoding task than after moving or
pleasantness tasks. In later studies, survival encoding resulted in higher levels of
recall than several other non-survival-encoding tasks involving semantic encoding,
imagery encoding, or organizational encoding. Superior recall is also observed for scenarios that involve planning but not survival. At issue here, is how much brain 'real-estate' is being used to store the
information, and how it is emotionally-gated through the amygdala. More on that
later.
All three forms of encoding can be used as mnemonics.Â
If two students are Call of Duty War Zone fanatics, they don't need a screen to discuss game strategies. Game structure is already firmly in memory.
Narne et al. (2008) essentially tested just that.
In the first task, a survival-encoding condition, participants were asked to imagine that they were stranding in the grasslands of a foreign land. They were told that over the next few months, they would need supplies of food and water, and also to protect themselves from predators. The researchers then showed the participants randomly selected words (eg: stone, meadow, chair) and asked them to rate on a 1 to 5 scale how relevant each item would be in the hypothetical situation.
In the second task, a moving-encoding condition, a second group of participants were asked to imagine they were moving to a new home in a foreign land and rate on a 1 to 5 scale how useful each item might be in helping them set up a new home.
In the third task, the pleasantness-encoding condition, a third group was shown the same words and asked to rate on a 1 to 5 scale the pleasantness of each word.
The findings show that participants recalled more words after the survival encoding task than either the moving or pleasantness tasks.
One advantage of encoding survival-related information is that it draws on elements of semantic, visual imagery and organizational encoding (Burns et al., 2011), which together produce high levels of subsequent memory.
Also, survival encoding encourages participants to think in detail about the goals they want to acheive which in turns benefits memory (Bell et al., 2015).
Sensory Storage: Back to Raw Input
Sensory memory holds sensory information for a few seconds or less. This is
much the same as a 'screen refresh' on a computer screen.
Sperling, 1960: Iconic Memory Test. He used Pavlovian conditioning (high,
medium, low tones) that allowed participants to correctly identify a row of 3 letters.
Since they did not know what the tone would be, it meant that for a brief time, all
the letters were stored in memory.
If the tone was substantially delayed, participants could not perform the task,
because the information had slipped away (not been 'refreshed' in modern
language).
Iconic memory is the fast-decaying (1 second) store of visual information.
Echoic memory is the fast-decaying (5 seconds) store of auditory information.
Information moves through several stages of memory; it gets encoded, stored, and made available for later retrieval.
Working Memory
Short-term memory holds non-sensory information for more than a few seconds
(15-20) but less than a minute. Preston & Peterson, 1959, the Decline of Short-
Term Memory.
Rehearsal is the process of keeping information in short-term memory by mentally
repeating it. Each repetition re-enters the information into short-term memory.
Remember micro-sub-vocalizations; your larnyx is actually forming the words,
even if mouth is shut, and lips don't move. Rehearsal plays a role in the serial
position effect which has two effects: primacy and recency.
Chunking involves combining small pieces of information into larger clusters that
are more easily held in short-term memory. Miller, 1956, reports that short-term
memory can hold seven meaningful items at once.
Working memory (Baddeley & Hitch, 1974) refers to active maintenance of
information in short-term storage. It is the central executive for both visual images
and verbal information.
The working memory model acknowledges both the limited nature of short-term
memory storage and the activities that are commonly associated with it.
Individuals with neurological damage to the verbal subsystem of working memory
have problems holding onto strings of digits and letters for a few seconds, and
difficulty learning new words. (Baddeley, 2001).
Fig 6.9 A Refined Model of Working Memory: visual-spatial sketchpad; episodic
buffer; phonological loop. The episodic buffer integrates the other two.
Individuals with neurological damage to the phonological loop have problems
holding onto strings and letters for a few seconds, but also difficulty learning new
words. (Baddeley & Hitch, 2019)
Brain imaging studies indicate that the central executive component of working
memory depends on regions within the frontal lobe that are important for controlling
and manipulating information on a wide range of cognitive tasks.
Children who score low on working memory tasks have difficulty learning new
information and performing well in the classroom. (Alloway et al., 2009)
Baddeley et al. (2011) report that the episodic buffer automatically combines
separate items into an integrated whole.
Wang & Allen report that studies of grade-school children and young adults
showed the ability to link together visual and auditory information and hold it in
working memory, a task thought to be dependent on the episodic buffer, shows
marked increases with age and is associated with word recognition skills, even
when controlling for the ability to hold individual items in working memory. (Wange
& Allen, 2018)
Long-term memory holds information for long periods of time, even years.
Bahrick, 2000 reported that even 50 years after graduation from high school, people
could accurately recognize about 90% of their classmates from yearbook
photographs. Consider how rarely this information had been accessed.
The Real Leonard Shelby
Scoville & Miller's case study of Henry Molaison (HM) is considered the first of its kind in understanding the various areas of the brain that contribute to memory. In a desperate attempt to stop epileptic seizures, parts of his temporal lobes, including the hippocampus and some surrounding regions were removed.
It turns out that the surgical techniques and scanning technologies were not up to the task, so H.M.'s condition only moderately applies to the fictional character Leonard Shelby.
https://pmc.ncbi.nlm.nih.gov/articles/PMC2649674/
In short, H.M. exhibited anterograde amnesia, the inability to transfer new information
from the short-term store into the long-term store. Note that his disability was based
in verbal or numeric information, not visual information.
Contrast this to the more common retrograde amnesia the inability to retrieve
information that was acquired before a particular date, usually the result of injury or
surgery. H.M.'s condition indicated that the hippocampus is not the site of long-term
storage. The hippocampal region index is critical when a memory is first formed, but not so
much later.
This is the index view. Evidence from fMRI show that hippocampal activity relates to retreiving as a holistic unit the separate elements such as a person, a location or an object which were initially encoded by distinct regions in the cortex. (Horner et al., 2015)
Evidence from hippocampal firing patterns in mice support the idea that these cells
are involved in a memory formation index, and tie together memory contents stored
elsewhere. (Tanaka et al., 2018)
Consolidation is the process whereby memories become stable in the brain.
Shortly after encoding, memories exist in a fragile state in which they can be easily
disrupted. A head injury or car crash will make it difficult for the subject to later
recall the events immediately previous to the incident.
Another type of consolidation involves transfer of information from the
hippocampus to more permanent storage in the cerebral cortex. Individuals with
retrograde amnesia (hippocampal damage) can recall childhood memories easily
but not recently-acquired memories.
Mounting evidence suggests that sleep plays an important role in memory
consolidation.
Jenkins & Dallenbach 1924: recall of recently learned information is greater
immediately after sleeping than after the same time spent awake.
Diekelmann & Born, 2010 report that sleep plays an active role in memory
consolidation, more than simple protecting against waking interference.
Payne et al,. 2009 report that sleep selectively enhances the consolidation of
memories that reflect the meaning of an experience as well emotionally important
memories.
Memories can become vulnerable to disruption when they are recalled, requiring
them to become consolidated again. When rats are cued to retrieve a new memory
that was acquired a day earlier, giving the animal a drug that prevents initial
consolidation will cause forgetting. If the animal is not actively retrieving that
memory the same drug will have no effect when given a day after initial encoding.
Each time memories are retrieved, they become vulnerable to disruption and have
to be reconsolidated. (Dudai, 2012)
Can painful memories be eliminated by disrupting reconsolidation? Brunet et al.,
2011 reported that when a traumatic event was reactivated after administration of a
drug that reduces anxiety, there was a subsequent reduction in traumatic
symptoms.
Agren et al., 2012 reported that disrupting reconsolidation can seemingly eliminate
a conditioned fear memory in the amygdala, a brain region that plays a key role in
emotional memory.
Finally, there is post-traumatic amnesia. Post Traumatic Amnesia (PTA) is a transient state of confusion, disorientation and memory loss that occurs immediately following a traumatic brain injury. (Hall University Teaching Hospitals May 11, 2018) Remember this for the Midterm Three Long Essay, when we discuss Leonard Shelby's traumatic incident. According to this research, Leonard should not be able to clearly remember the 'incident'.Â
Long Term Potentiation Revisited
The act of sending a neurotransmitters across a synaptic gap changes the synapse, making it easier
to send the next batch. This is where the comparison between brains and computers falls apart.
Silicon computer circuits, like the ones in your smartphone, don't change.
Eric Kandel won the Nobel Prize in 2000 for his work with the sea snail Aplysia, a relatively
uncomplicated animal with an extremely simple nervous system of only 20,000 neurons.
If the experimenter shocks Aplysia over and over, it will develop an enduring memory caused by
the growth of new synaptic connections between neurons.
Learning is based on changes involving the synapses for both short-term storage (enhanced
neurotransmitter release) and long-term storage (growth of new synapses). Experience that results
in memory produces physical changes.
A similar process occurs in the human hippocampus, called long-term potentiation, a process
whereby repeated communication across the synapse between neurons strengthens the connection,
making further communication easier.Â
LTP occurs in several pathways within the hippocampus, it can be induced rapidly and it can last for a long time.Â
Drugs--such as morphine, cocaine, and nicotine--can block LTP.
Retrieval
Retrieval cue: external information that is associated with stored information and
helps bring it to mind. Tulving & Pearstone (1966) results suggest that information is sometimes
available in memory even when it is momentarily inaccessible; retrieval cues can bring inaccessible
information to mind.
Involuntary memories occur even more often in everyday life than memories we voluntarily try to
retrieve (Rasmussen & Bernstein, 2011) underscoring the power of retrieval cues to unlock our
personal pasts.
Encoding specificity principle: a retrieval cue can serve as an effective reminder
when it helps recreate the specific way in which the information was encoded.
External contexts often make powerful retrieval cues. Recovering alcoholics often
experience a renewed urge to drink when visiting places in which they once drank.
State-dependent retrieval: the tendency for information to be better recalled
when the person is in the same (usually emotional) state during encoding and
retrieval. Being in a good mood affects patterns of electrical activity in parts of the
brain responsible for semantic processing, suggesting mood has a direct influence
on semantic encoding. (Kiefer et al., 2007).
Transfer-appropriate processing: memory is likely to transfer from one situation
to another when the encoding and retrieval contexts of the situation match.
In fact, every time we retrieve a memory, it is altered. For example, the act of retrieval itself (of a
fact, concept, or event) makes the retrieved memory much more likely to be retrieved again, a
phenomenon called the testing effect or the retrieval practice effect (Pyc & Rawson, 2009; Roediger
& Karpicke, 2006).
Retrieval & Subsequent Memory
Bjork, 1975: the act of retrieval can strengthen a retrieved memory, make it easier
to remember the information at a later time.
Retrieving information from memory has different effects than studying the information again.
Roediger & Karpicke, 2006: memory testing benefits long-term retention. The study-test condition
yields much higher levels of recall than does the study-study condition.
Retrieval-induced forgetting: a process by which retrieving an item from long-term memory
impairs subsequent recall of related items. Anderson et al., 1994: retrieving similar target items
caused subsequent forgetting of the related but suppressed items.
Storm et al., 2006: if the target is not successfully retrieved, the act of suppressing the competitors
while you attempt to retrieve the target still reduces your ability to retrieve the competitors at a later
time.
Cuc, Koppel & Hirst, 2007: when a speaker selectively talks about some aspects of memories
shared with a listener and does not mention related information, both the listener and the speaker
later have a harder time remembering the omitted events.
In addition to improving or impairing subsequent memory, the act of retrieval can also change what
we remember from an experience.
Schacter, 2013: The Museum Tour experiment. Participants sometimes incorrectly remembered that
the stop shown in the novel photograph had been part of the tour. Participants who tended to make
this mistake also tended to have more vivid recollections during the reactivation session.
Reactivating a memory temporarily makes it vulnerable to disruption and change.
Schacter, 1996: trying to recall an incident and successfully recalling one are fundamentally
different processes that occur in different parts of the brain.
Regions in the left frontal lobe show heightened activity when people try to retrieve information
that was presented to them earlier. Successful remembering a past experience tends to be
accompanied by activity in the hippocampal region.
Separating the Components of Retrieval
Furthermore, successful recall can also activate parts of the brain that play a role in processing
sensory features of an experience. For instance, recall of previously heard sounds is accompanied
by activity in the auditory cortex (the upper part of the temporal lobe), whereas recall of
previously seen pictures is accompanied by activity in the visual cortex in the occipital lobe.
Successful suppression of an unwanted memory causes reduced activity in the hippocampus. Recent
fMRI evidence indicates that during memory retrieval, regions within the frontal lobe that are
involved in retrieval effort play a role in suppressing competitors.
Once the competitor is suppressed, the frontal lobe no longer has to work as hard to control
retrieval, ultimately making it easier to recall the target item. In addition, successful suppression of
an unwanted memory causes reduced activity in the hippocampus.
Multiple Forms of Memory
Explicit memory occurs when we consciously or intentionally retrieve past experiences. Implicit
memory occurs when past experiences influence later behaviour and performance, even without
effort to remember them or an awareness of the recollection.
Procedural memory is the gradual acquisition of skills as a result of practice. People with amnesia
can acquire new procedural memories, because they are not processed through the hippocampus.
Priming is the enhanced ability to think of a stimulus such as a word or object, as a result of recent
exposure to the stimulus. It is an example of implicit memory. Mitchell (2006) discovered that
priming can persist over long periods of time. Amnesic individuals can show substantial priming
effects even though they have no explicit memory of learning. Remember Sammy Jenkis!
Priming occurs in parts of the occipital lobe involved in visual processing (perceptual) and parts of
the frontal lobes (conceptual) involved in word retrieval.
Semantic & Episodic Memory
Semantic memory is a network of associated facts and concepts that make up our general
knowledge of the world.
Episodic memory is the collection of past personal experiences that occurred at a particular time
and place.
(Brandt et al., 2009) studied three young adults who suffered damage to the hippocampus during
birth as a result of difficult deliveries that interrupted oxygen supply to the brain. All three children
learned to read, write and spell, developed normal vocabularies and acquired other kinds of
semantic knowledge that allowed them to perform well in school. Thus, the hippocampus is not
necessary for new semantic memories.
Tulving, 1985 reported that individuals with hippocampal amnesia reveal that some of them have
difficulty imagining new experiences. This occurs also in aging.
Neuroimaging studies reveal a network of brain regions involved in episodic memory, including the
hippocampus, showing increased activity when people remember the past or imagine the future.
We rely heavily on episodic memory to envision our personal futures, as it is a flexible system that
allows us to recombine elements of past experiences in new ways. This flexibility of episode
memory might also be responsible for memory errors.
Collaborative Memory
Collaborative memory is how people remember in groups. A collaborative group will typically
recall more items than a single individual.
A nominal group is the combined recall of several individuals recalling memory targets on their
own, more than the collaborative group. Most people believe, based on intuition, that working
together should increase recall, when actually the opposite is true. (Rajaram, 2011)
This was first attributed to social loafing (letting the strong leaders do the work), but the more
likely cause is the disruptive effect of others' retrieval strategies on one's own.
Collaboration has other benefits. One person will remember something another did not, and later
testing will see improved performance. What effect does present-day Google have on our
memories? Sparrow et al., 2011 reported that participants were using their computers in an efficient
way to help remember facts, while relying on their own memories to recall where those facts could
be found. The conclusion overall? Groups can recall more than a single individual, but less than
multiple individuals working on their own.
Memory Failures
Transience: forgetting with the passage of time. Transience occurs during the storage phase of
memory, after an experience has been encoded and before it is retrieved. Ebbinghaus noted a rapid
drop-off in retention during his memory tests, followed by a slower rate on later tests. In all
subsequent studies, memories did not fade at a constant rate as time passed; most forgetting
happened soon after the event occurred, with increasingly less forgetting as more time passed.
Quality the same.
Distorted memories can be caused by: retroactive interference, information learned later impairs
memory for information acquired earlier; proactive interference, information learned earlier
impairs memory for information acquired later. Note: always ask, what does the interference work
on?
Absent-mindedness is a lapse in attention that results in memory failure. Without proper attention,
material is much less likely to be stored properly and recalled later. This is an example of divided
attention. Shallice et al., 1994 reported that less activity in the lower left front lobe when attention
was divided between an easy and a difficult task. This lobe was prevented from playing its normal
role in semantic encoding. Recent research indicates that divided attention leads to less
hippocampal involvement in encoding (necessary for episodic memory).
Prospective memory: remembering to do things in the future. A failure can be averted by having a
cue available at the moment you need to remember to carry out an action (deferred request).
Memory for a deferred action improves only when the reminder was available at the time needed
for retrieval.
Blocking: failure to retrieve information that is available in memory even though you are trying to
produce it. This occurs especially often for names of people and places, because links to related
concepts and knowledge are weaker than for common names. Descriptive names have more
semantic encoding (neuronal linkages) than arbitrary names. Name blocking usually results from
damage to parts of the left temporal lobe on the surface of the cortex, most often as a result of
stroke (also old age).
Damasio et al., 1996 reported that strong activities of regions within the temporal lobe when
people recall proper names.
Memory Misattribution
Misattribution involves assigning a recollection or an idea to a wrong source. Schacter 1996.
Thompson rape case. Google 'Nurse Betty' to see a movie about this.
Faulty eyewitness memory was a factor in more than 75% of the first 310 American cases in
which individuals were shown to be innocent by DNA evidence after conviction for crimes they did
not commit.
Source memory: the recall of when, where, and how information was acquired.
Source misattribution is correct information, but the wrong source. This could be the cause of
deja vu, where a present situation that is similar to a past experience may trigger a general sense of
familiarity (mistakenly attributed to having been in the exact situation).Individuals with damage to the frontal lobes are especially prone to memory misattribution errors, due to effortful mental processing. Schacter 1984: M.R.
False recognition, a feeling of familarity about something that has not been encountered before (without recall of associated details).
Suggestibility: the tendency to incorporate misleading information from external sources into
personal recollections. A suggestive question will lead participants to isattribute information.
Loftus, 2003: Not only misleading details, but entire episodes that never occurred can be implanted
by suggestion. We do not store all the details of our experiences in memory, making us vulnerable
to suggestion. Visual imagery plays an important role in constructing false memories. The Diana
Halbrook case (Schacter, 1996).
A number of techniques used in psychotherapy to 'recover' childhood memories are clearly
suggestive. Specifically, imagining past events under hypnosis can create false memories. (Garry et
al., 1996)
Bias: the distorting influence of present knowledge, beliefs, and feelings on recollection of previous
experiences. Our current moods can bias our recall of past experiences.
Consistency Bias: reconstructing the past to fit the present. See 'Shutter Island'.
Change Bias: exaggerates the difference between past and present.
Egocentric Bias: change bias that exaggerates our importance & influence
(looking good in the presence of others.)
Persistence is the intrusive recollection of memories that we wish we could forget, normally after
disturbing or traumatic events. This is the emotional-gating of memory; we remember emotional
experiences better than non-emotional ones. Ochsner, 2000: Memory for unpleasant pictures is
more accurate then for pleasant ones.
Flashbulb memories: detailed recollection of when and where we experience emotionally intense
events, elaborated by semantic encoding.
The Amygdala's Influence on Memory will be on the next exam.
Stress-related hormones, such as adrenaline and cortisol, mobilize the body in face of threat.
Individuals with amygdala damage remember mundane and emotionally arousing events equally
well.
For normals, amygdala levels during arousing events is a good predictor of subsequent memory quality.
In conclusion, forgettings are side effects of our brain's usually successful attempt to sort through
incoming information, preserving details worthy of attention and recall, and discarding others less
worthy.