Topic 11: Memory & Amnesia Flashcards
Short-term Memory
Typically lasts about 15 seconds if the information is not rehearsed or attended to. Limited in capacity: 7 +/- 2 units
Different types:
- sensory memory (>1 sec)
- motor memory (i.e., motor planning and action)
- cognitive memory
- iconic memory (visual sensory memory, about 300 milliseconds)
Long-term memory
Information that is going into a store that we can retrieve at a later time; consolidated.
- Hypothesized to be unlimited/infinite.
- Hard to know the difference between no longer being able to access memory although it is still stored or is the memory being “deleted?”
Different types:
- explicit memory
- implicit memory
- emotional memory (conscious and unconscious)
Amnesia
Partial or total loss of memory – resulting from localized brain lesions
Explicit Memory
Different types:
- Episodic (personal, autobiographical)
- Semantic (facts, knowledge)
Implicit Memory
Unconscious
- Skills
- Habits
- Priming
- Conditioning
Emotional Memory
Conscious and unconscious
- attraction
- avoidance
- fear
Memory function relies on three stages:
- Attention, encoding learning (i.e., study processes, deeply working with information in a semantic sense)
- “Storage” Consolidation: rehearsal, re-encoding
- Retrieval Memory probe process (i.e., memory search)
Attention, encoding learning: This stage involves paying attention to information and processing it in a way that allows for it to be stored in memory. Attention is the first step in memory formation and involves focusing on a particular stimulus or information. Encoding is the process of transforming information into a format that can be stored in memory. This stage is critical as it determines how well information will be remembered later on.
“Storage” consolidation - rehearsal - re-encoding: After information has been encoded, it needs to be consolidated or stabilized in memory to prevent it from being forgotten. This stage involves rehearsal or repetition of the information to strengthen the memory trace. Re-encoding involves the modification of the original memory trace with new information or associations that can further enhance memory.
Retrieval Memory probe process: This stage involves accessing information that has been previously stored in memory. Retrieval is the process of searching for and retrieving information from memory. This stage can be influenced by factors such as the strength of the memory trace, the cues available for retrieval, and the context in which the information was originally encoded.
Free Recall
Free recall is a type of memory test in which a person is asked to remember information without any cues or prompts.
Cued Recall Retrieval
Retrieval without the aid of cues
Recognition Retrieval
Retrieval with the aid of cues
Recognition Retrieval
Stimulus triggers remembering
Hippocampus
- Spatial Memory
- Explicit Memory relies on hippocamus
Amygdala
The higher the emotional content associated with a memory, the greater the amount of activation that we see in those limbic system components… and that influences the hippocampus, which will help to solidify and strengthen the consolidation of that memory.
Basal Ganglia
The basal ganglia plays a huge role in implicit memory.
- Recall that it does not have any direct connections to higher cortical areas, so all of the basal ganglia influences are going to route through the thalamus to various regions of the brain.
- Basal ganglia is going to influence behaviour without producing explicit memory recall (i.e., learning new skills)
Cerebellum
Plays a role in longer-term implicit memory
Prefrontal Areas
Believed to play a role in the shorter-term memory store.
The CASE of HM
- Bilateral transaction of temporal lobes: refers to the surgical removal of both temporal lobes, including most of the brain’s hippocampus. This procedure is sometimes used as a treatment for severe epilepsy that cannot be controlled by medication
- HM experienced significant anterograde amnesia, meaning he could not form new memories (specifically episodic memories). However, his procedural memory (memory of skills and habits) and long-term memories from before the surgery remained intact; he also has some retrograde amnesia
- Good memory for events before surgery, but unable to describe the job he has worked for 6 months
- surgery = severe brain injury
- sparring of implicit memory
- hippocampus containing place cells/neurons may have still been present as he was able to form memories about his environment
- Above average IQ
- Good spatial memory of his immediate surroundings
- Retrograde amnesia in H.M. extends 11 years
anterograde amnesia
The idea is that the person can’t form new memories, so memory is impacted from the point of trauma onward.
- Cannot form long-term explicit memory
- Inability to take on new information, hard to live on their own
retrograde amnesia
From the point of trauma and backward in time.
- After the injury, usually, some of the memories can recover, where we see the amount of time lost can shorten over time (e.g., head trauma, but not really in complete removal of the brain part).
Global Anterograde Amnesia
Impairment in the ability to form new memories across a variety of areas, i.e., across various sensory systems, so it doesn’t matter whether the information is presented in an auditory way, a visual way, or if it is semantic, episodic, long-term explicit information, it doesn’t seem to matter, it is global.
Squire & Cohen (1979) Study
An experiment that studies the affects of ECT (Electroconvulsive Shock Therapy) on memory:
- Recalling details about popular TV shows that aired for only one season during different years
- Temporally limited retrograde amnesia in 20 patients
- Measured before ECT: Notice that the ones that were closer in time to them at that moment recalled quite a few facts; as you move further back in time, they recall fewer facts
- Measured after ECT: the number of facts recalled dramatically decreases; this shows that ECT impacts the more recent memories (a theory about recent memories is that they have not been strongly consolidated yet, so they are most vulnerable to disruption.
- ECT affects normally recover in 24 hours
Temporal Gradient of Amnesia (Ribot’s Law)
Amnesia recovery in the context of Ribot’s Law:
- there is a time gradient in certain types of amnesia
- retrograde amnesia: recent memories are the more likely ones to be lost compared to memories that are more remote and further away
- Idea that the older memories tend to be the ones that have been very strongly consolidated at that point, and the more recent ones haven’t been strongly consolidated and may be vulnerable to disruption
In the image:
- @ 5 Months: complete loss of memory of 2 years (RA), and in AA, they have lost the inability to form new memory and recall it
- @ 8 Months: In RA, the period of a total loss of memory has shrunken by half, and they now have partial retrograde amnesia for four more years, where it is patchy, so they can recall some things in that period of time. In AA, it shrunk to three months, so it suggests that even though at five months, they could not recall any new information, there might have been a period of time where they WERE consolidating information but just could not recall it
- @ 16 Months: total RA is down to 2 weeks, there is still the effects of them not being able to form memories therefore cannot recall it (AA) but since then, the AA has resolved
Korsakoff’s Syndrome Study
Task: recognizing faces of individuals who were present across different decades; Ronald Reagan was used in this study.
- Nonalcoholic controls do well across all decades
- Alcoholic controls develop a trend with impairments in the more current decades, suggesting some in antegrade amnesia while also seeing some impairment in the older information (i.e., retrograde)
- Korsakoffs have antegrade and retrograde amnesia; you can stop the damage from continuing, but you cannot full recover (i.e., the damage has been done)
Working Memory (WM)
Working memory is a component of short-term memory that involves the temporary storage and manipulation of information. It has two main components:
- Auditory-verbal working memory:
- Phonological store: this is responsible for the temporary storage of verbal information, such as speech sounds, words, and numbers.
- Input buffer: this component receives and processes incoming auditory information.
- Output buffer: this component is responsible for the production of speech and other verbal responses. - Visual-nonverbal working memory:
- Visuospatial scratchpad: this is responsible for the temporary storage of visual and spatial information, such as images and locations.
- Dorsolateral prefrontal cortex (DLPFC): this region of the brain is involved in the active maintenance and manipulation of working memory information. It plays a critical role in both visual and auditory working memory tasks.
Single Cell recording of DLPFC
The experiment involves training monkeys to fixate their gaze on a particular location on a screen in response to a visual cue. The cue is then removed, and the monkey must maintain its gaze fixation for a certain period, after which a visual stimulus appears at a different location on the screen. The monkey is then required to shift its gaze to the new location of the visual stimulus.
- we see a lot of firing at the moment when the monkey must hold its gaze and remember where the second visual cue is; this is because while it is holding its gaze, it must remember where that second cue popped up and then move its eyes when prompted
- when the monkey moves their eyes, we see activity again
During this experiment, single-cell recording techniques are used to record the activity of neurons in the DLPFC. By analyzing the neural activity patterns during different phases of the experiment, researchers can investigate the role of DLPFC in maintaining working memory and spatial attention. This experiment has been used extensively to study the neural mechanisms of working memory in primates, including humans.
We see that the cells are active initially when the queue is presented and that they are highly active during the delay (so they are holding onto that information in working memory)
- the DLPFC plays a role in motor planning and in relation to visual information
- DLPFC has spatial specificity
- DLPFC is a part of that dorsal stream, apart from knowing about where things are located in spaces that play a role in motor planning; then the information continues along the dorsal stream to the prefrontal cortex, so it’s about holding the visual information in a shorter term memory store, and it’s about location information to help planning motor responding
- PREFRONTAL CORTEX AND PLANNING; dorsal within the frontal
Delayed non-match-to-sample (DNMS) task
The Delayed non-match-to-sample (DNMS) task is an experimental paradigm used to study the role of the hippocampus in memory. In this task, monkeys are presented with a visual stimulus, such as an object, and after a delay period, they are presented with two objects. The monkey must choose the object not presented during the initial presentation phase.
In the variant of the task where monkeys have a lesioned hippocampus, the monkeys are trained to make eye movements to indicate their choice. The delay period between the initial presentation and the choice phase gradually increases. Monkeys with hippocampal lesions show impaired performance on this task, suggesting that the hippocampus is critical for certain aspects of memory.
- if the delay was <15 secs, they can do the task because they are relying on short-term memory
- if the delay was >15 secs, this requires the consolidation of information into the longer-term store, which requires the hippocampus so they cannot do well
- even without a hippocampus, you can have a working memory
Mirror Reading Task
The Mirror Reading Task is a cognitive task that involves reading words or sentences that are reflected in a mirror. The purpose of the task is to test implicit learning, which is learning that occurs unconsciously and without awareness of what has been learned.
- implicit memory task
- RULE OUT PRACTICE EFFECTS by looking at non-repeated performance; this is when we give them novel lines, and we still see improvements and they are building a skill
- in the image, it goes down vertically in this order: Retrograde amnesia, Korsakoff’s Syndrome, and then those that have undergone ECT, they all improve
- in the control subjects, they improve
During the task, the participant is presented with words or sentences that are reflected in a mirror, making them difficult to read. Over time, with repeated exposure, the participant learns to read the words or sentences more quickly and accurately, despite the mirror reversal. This is thought to occur through the formation of implicit memory, in which the learning of the task is encoded and stored unconsciously.
Studies have shown that individuals with amnesia can learn and improve their performance on the Mirror Reading Task, even though they have no conscious awareness of the learning. This suggests that implicit memory can still be formed and accessed in individuals with amnesia, even when explicit memory is impaired.
H.M. - Deficits in learning new words
Hippocampal damage & semantic memory
- teaching HM new words is semantic memory
- in the study, controls and HM was given new words; the idea is that after looking at it a couple of times, you could come up with a definition and a synonym and use it in a sentence
- after 20 trials, HM could not do all three and would make a significant amount of errors = he could not learn, showing the impairment of his long-term explicit semantic memory
- sparred implicit memory = can rely on the basal ganlia and cerebellum, not only hippocampus; it can be demonstrated through behaviour
