Module 11 Flashcards
Who was H.M. and what procedure did he undergo?
H.M. was a man who underwent a bilateral medial temporal lobectomy in 1953 at the age of 27 to treat severe epilepsy.
The surgery successfully reduced H.M.’s seizures, but it resulted in devastating amnesic effects.
What is retrograde amnesia, and how did it affect H.M.?
Retrograde amnesia is the inability to recall events that occurred before brain damage or surgery. H.M. had mild retrograde amnesia for events preceding his surgery but retained memory for remote events.
H.M. had an almost total inability to form new long-term memories after the surgery. He became suspended in time and could not remember events or people he encountered after the surgery.
What is the digit-span + 1 test, and how did H.M. perform on it?
The digit-span + 1 test assesses verbal long-term memory by having the participant repeat a sequence of digits with an additional digit added each trial. H.M. performed poorly on this test, failing to repeat an 8-digit sequence after 25 trials.
Describe H.M.’s performance on the mirror-drawing test.
H.M. showed improvement over three days on the mirror-drawing test, indicating retention of the task. However, he could not recall ever having completed the task before.
What were three influential contributions of H.M.’s case to the study of memory?
Challenging the view of memory as diffusely distributed throughout the brain.
Supporting the theory of different modes of storage for short-term, long-term, and remote memory.
Revealing the distinction between explicit and implicit long-term memories.
What are explicit and implicit long-term memories, and how did H.M.’s case contribute to their distinction?
Explicit memories are consciously recalled memories, while implicit memories are demonstrated through improved performance without conscious awareness.
H.M.’s performance on tasks like mirror-drawing and incomplete-pictures tests showed evidence of implicit memories despite lacking conscious recollection, leading to the distinction between explicit and implicit memories.
What is the significance of having both explicit and implicit memory systems?
The implicit memory system provides simple, unconscious memory processes, while the explicit memory system allows for flexible use of information, leading to greater adaptability.
What are semantic and episodic memories, and how do they differ in individuals with medial temporal lobe amnesia?
Semantic memories are for general facts or information, while episodic memories are for specific events in one’s life.
Individuals with medial temporal lobe amnesia often have difficulty with episodic memories but retain their semantic memory.
Describe the case of transient global amnesia and its relevance to understanding medial temporal lobe amnesia.
Transient global amnesia is characterized by sudden onset anterograde amnesia and moderate retrograde amnesia, typically lasting 4 to 6 hours. Abnormalities in the hippocampus suggest ischemia-induced damage, offering insights into the pathology of medial temporal lobe amnesia.
What is Korsakoff’s syndrome, and what are its symptoms?
Korsakoff’s syndrome is a disorder of memory commonly seen in heavy alcohol consumers, often associated with thiamine deficiency. Symptoms include sensory and motor problems, confusion, personality changes, and a risk of death from related disorders.
How does the amnesia of Korsakoff’s syndrome progress, and what types of memory are affected?
Initially, there is anterograde amnesia for explicit episodic memories, progressing to retrograde amnesia extending back into childhood. Deficits in implicit memory are less severe and depend on the test used.
What part of the brain is often implicated in the memory deficits of Korsakoff’s syndrome, and why is it challenging to identify the specific cause of amnesia?
Damage to the mediodorsal nuclei of the thalamus is often observed, but the diffuse brain damage complicates pinpointing a single cause of amnesia in Korsakoff’s syndrome.
Describe Alzheimer’s disease and its effects on memory.
Alzheimer’s disease is a progressive disorder characterized by memory deterioration, leading to severe dementia and inability to perform daily activities. Memory deficits include both explicit and implicit memory impairments.
What are the characteristics of memory deficits in predementia Alzheimer’s patients?
Predementia Alzheimer’s patients display general memory deficits, including anterograde and retrograde deficits in explicit memory tests, as well as deficiencies in short-term and certain types of implicit memory.
What role does acetylcholine depletion play in Alzheimer’s amnesia, and what other brain areas are affected?
Acetylcholine depletion, resulting from basal forebrain degeneration, is thought to contribute to Alzheimer’s amnesia. However, the brain damage associated with Alzheimer’s disease is diffuse, affecting areas like the medial temporal lobes and prefrontal cortex.
What is posttraumatic amnesia, and what are its characteristics following a closed-head traumatic brain injury (TBI)?
Posttraumatic amnesia follows a closed-head TBI and involves permanent retrograde amnesia for events leading up to the injury and anterograde amnesia for events during the period of confusion after regaining consciousness.
How do memory deficits following a closed-head TBI often puzzle friends and relatives of the patient?
Patients may seem lucid during interactions because short-term memory is intact, but they later have no recollection of the conversation due to anterograde amnesia.
Improved test performance without conscious awareness, as in the case of H.M.’s mirror-drawing task, exemplifies long-term memories which became known as _______ memories.
implicit
Explicit long-term memory is broadly divided in two main categories: episodic and _______.
semantic
Ischemia in the _______ could result in transient global amnesia.
hippocampus
Amnesia due to Korsakoff’s syndrome is typically associated with large lesions to the _______.
medial diencephalon
_______ amnesia refers to the loss of memories that took place before the brain injury.
Anterograde
_______ depletion resulting from damage to the basal forebrain may contribute to Alzheimer’s amnesia.
Acetylcholine
Memory consolidation is studied using _______ shock, which induces seizures using large electrodes.
electroconvulsive
Each time a memory is recalled or a similar experience occurs, a new _______ is formed, making that memory more difficult to forget.
engram
Amnesia caused by a nonpenetrative head injury is called _______.
posttraumatic amnesia (PTA)
Most research on reconsolidation has involved _______ conditioning using rats.
fear
What does the gradient of retrograde amnesia after closed-head TBI suggest about memory consolidation?
The gradient suggests that memory consolidation strengthens older memories while recent memories are preferentially disrupted.
According to Hebb’s theory, how are memories stored and consolidated?
Hebb’s theory suggests that memories are initially stored in short-term memory by neural activity reverberating in closed circuits. Over time, structural synaptic changes occur, leading to stable long-term storage.
What is electroconvulsive shock (ECS), and how has it been used to study memory consolidation?
ECS is an intense, brief, seizure-inducing current administered to the brain. It has been used to study memory consolidation by disrupting neural activity, erasing memories not yet consolidated to structural synaptic changes.
Describe the findings of Squire, Slater, and Chace’s (1975) study on ECS-produced retrograde amnesia.
Their study found a long gradient of retrograde amnesia induced by ECS. Memories of recent events were disrupted, while older memories remained intact.
What is the current view of memory consolidation, and how does memory resistance to disruption change over time?
Memory consolidation is believed to continue indefinitely, with memories becoming more resistant to disruption over time as additional links are established with other memories.
What is the standard consolidation theory, and why has it fallen out of favor?
The standard consolidation theory suggests that memories are temporarily stored in the hippocampus before being transferred to cortical storage. It has fallen out of favor due to evidence suggesting a more distributed and gradual process of memory consolidation.
What is reconsolidation, and why is it significant in the study of memory?
Reconsolidation is the process where retrieved memories become temporarily labile and susceptible to disruption until reconsolidated. It is significant as it suggests memories can be modified or updated upon retrieval.
Why are controlled experiments with animal models essential in studying memory?
Controlled experiments with animal models are necessary to identify specific brain structures involved in memory, control learning and retention variables, and test hypotheses that are not feasible with human subjects.
Why did early attempts to develop an animal model of medial temporal lobe amnesia fail?
Early attempts failed due to the focus on implicit memory tests, assuming that amnesia resulted solely from hippocampal damage, and the misconception that H.M.’s amnesia extended to all forms of long-term memory.
When was an animal model of H.M.’s disorder developed, and why was it considered a breakthrough?
An animal model of H.M.’s disorder was developed in the mid-1970s. It was considered a breakthrough because it allowed for experimental investigation into the neuroanatomy of medial temporal lobe amnesia.
What is the delayed nonmatching-to-sample test, and how does it assess memory in monkeys?
The delayed nonmatching-to-sample test involves presenting a sample object to a monkey, followed by a delay, and then presenting the sample object alongside an unfamiliar object. The monkey must select the unfamiliar object to obtain a reward.
How did monkeys with bilateral medial temporal lobectomies perform on the delayed nonmatching-to-sample test?
Monkeys with bilateral medial temporal lobectomies had major object-recognition deficits. Their performance mirrored that of H.M., with normal performance at short delays but significant deficits at longer delays.
What is the significance of the rat version of the delayed nonmatching-to-sample test?
The rat version allows for the assessment of memory in rodents, providing insights into the role of hippocampal damage in medial temporal lobe amnesia.
Describe the findings regarding the performance of rats on the delayed nonmatching-to-sample test.
Rats perform almost as well as monkeys on the delayed nonmatching-to-sample test, with delays of up to 1 minute. This challenges the assumption that rats cannot perform complex tasks.
How do lesions to various medial temporal lobe structures affect performance on the delayed nonmatching-to-sample test in rats?
Lesions to the medial temporal cortex produce severe deficits in performance, while lesions to the hippocampus or amygdala produce only modest deficits.
What does the relation between ischemia-produced hippocampal damage and object-recognition deficits suggest about the role of the hippocampus?
While ischemia-produced hippocampal damage is associated with severe deficits in object-recognition memory, total removal of the hippocampus produces only modest deficits. This suggests that damage to other brain structures also contributes to amnesia.
What evidence suggests that damage to brain structures other than the hippocampus contributes to amnesia following cerebral ischemia?
Studies have shown that ischemic patients with reduced hippocampal volume also tend to have extensive neocortical damage, indicating that damage to multiple brain areas contributes to amnesia.
What did the first major studies of medial temporal lobe neurons focus on, and what stimulated this research?
The first major studies focused on hippocampal neurons in rats. This research was stimulated by the finding that bilateral hippocampal lesions disrupt tasks involving memory for spatial location.
Describe the Morris water maze test and its findings in rats with hippocampal lesions.
In the Morris water maze test, rats learn to swim to a hidden platform in a circular pool of water. Rats with hippocampal lesions struggle to learn this task.
Explain the radial arm maze test and the deficits observed in rats with hippocampal lesions.
The radial arm maze test involves rats visiting arms baited with food. Rats with hippocampal lesions display deficits in both reference memory and working memory measures of radial arm maze performance.
What are place cells, and where are they found?
Place cells are neurons that respond only when an animal is in specific locations, known as place fields. They are found in the hippocampus.
How do place cells contribute to spatial processing?
Place cells fire to indicate where the animal “thinks” it is located in its environment. They play a role in spatial navigation and memory.
What are grid cells, and where are they found?
Grid cells are entorhinal neurons with repeating patterns of evenly spaced hexagon-shaped place fields. They are found in the entorhinal cortex.
How do grid cells contribute to spatial processing?
Grid cells fire as an animal traverses specific points in its environment. They help in encoding spatial information and are involved in spatial computations.
What is the relationship between grid cells and place cells?
The relationship between grid cells and place cells is complex. While grid cells provide input to place cells, the exact nature of their interaction is still debated.
How does the hippocampus contribute to cognitive processing beyond spatial navigation?
The hippocampus is involved in coding for temporal aspects of experiences, learning about social organization, and coding concepts, suggesting its role in generating a cognitive map.
What is meant by the term “cognitive map” in the context of the hippocampus?
The term “cognitive map” refers to the idea that the hippocampus generates a mental representation not only of spatial information but also of other cognitive concepts and experiences.
Why are recording electrodes sometimes implanted in the brains of patients with severe epilepsy?
Recording electrodes are implanted to record the activity of specific neurons, typically in the medial temporal lobes, as a precursor to surgery.
What are the major structures of the medial temporal lobes?
The major structures are the hippocampus, amygdala, and medial temporal cortex.
Describe the selectivity and invariance of Jennifer Aniston neurons.
Jennifer Aniston neurons are highly selective, responding to only a small number of specific test objects or individuals, and their responses are highly invariant across different tests.
What is the significance of Jennifer Aniston neurons being called concept cells?
Jennifer Aniston neurons are called concept cells because they respond to ideas or concepts rather than specific particulars.
Provide an example of how concept cells respond to ambiguous stimuli.
Concept cells respond to ambiguous stimuli based on the viewer’s perception of the concept. For example, they respond to an ambiguous face only when the viewer perceives the concept associated with that face.
