Tuesday May 5th Chapter 12 part 2
Memory Research and the Case of Henry Gustaf Holverson
Historical Context of Memory Research: The study of learning and memory frequently references a specific individual who was historically referred to by the initials HS or HTF in psychology textbooks to protect his identity while he was still hospitalized.
Henry Gustaf Holverson: Following his death in , his family permitted the disclosure of his identity. He had a unique and specific neuropathology that was instrumental in informing the scientific community about the brain structures involved in memory.
Importance of the Case: Holverson's specific brain damage provided insights into the structures and functions involved in the emergence and consolidation of memories, particularly identifying areas of the brain involved in creating new records of experience.
The Nature of Early Memories and Infantile Amnesia
Earliest Memories Timeline: Among humans, the earliest explicit memories typically cannot be recounted until approximately the age of to years.
Specific Examples of Early Memories: * One individual recounts a memory from at the age of years and months, observing a shaved carpet near a fireplace when their parents brought home a brother weighing pounds and ounces. * Other recounted memories include being years old and wearing a Ninja, T. H. Gibson, Jertile mask with swords and dice. * A memory of being punished at age and being forced to clean mirrors on a wall. * A memory of being almost and seeing a fish flopping out of a cage at a fair. * An experience at age involving an accident at Brooksbank park. * A memory at age or involving the setup of a trampoline that led to a family scare and a spanking.
Patterns in Early Memory: * Memories before the age of are rarely recounted as explicit events; this phenomenon is linked to the event being in Jacob's den. * Implicit vs. Explicit Memory: While explicit memories are rare in infancy, other forms of memory (such as retrieval cues used to kick a ball) are active. * Emotional Amplification: Memories with high emotional valence are often amplified and easier to solidify. This is viewed as an evolutionary mechanism through the amygdala, which acts like a "dial" on the memory circuit to increase sensitivity during emotional events.
Infantile Amnesia Factors: This may be a reflection of the maturation of the rehearsal circuit and the connections to long-term storage. If the structures for rehearsal or the connections to storage sites are not yet developed, memories will not be retained.
Functional Neuroanatomy of the Memory Circuit
Structural Maturation: Learning and memory structures take decades to fully mature.
The Rehearsal Circuit Components: * Amygdala: Serves as the emotional "dial" for the circuit. * Hippocampus: Functions as the "gateway" for memory consolidation. * Cortex/Cortices: The primary areas where memory information is stored and from which it is eventually recollected or pulled back into consciousness. * Basal Forebrain: Crucial for providing acetylcholine, which is essential for gating activity and maintaining the brain's attention. * Thalamus: Involved in the rehearsal and attention mechanisms.
Role of Attention and Environment: Interaction with the environment shapes the memory circuit through processes like LTP (Long-Term Potentiation) or LTD (Long-Term Depression). Attention is required to filter sensory information from the cortex through the rehearsal circuit to consolidation.
Rehearsal: Defined as the conscious cogitation or speaking of information to maintain it. It requires attention, mediated by acetylcholine from the basal forebrain.
Anterograde Amnesia: Mechanisms and Case Studies
Definition: The inability to form new declarative (explicit) memories after an amnestic event.
Pathology: Typically involves damage to the rehearsal circuit, creating a "consolidation gap." While new memories cannot be formed, old memories remain retrievable.
Case Study: Henry Gustaf Holverson: * Suffered from severe epilepsy. To prevent death from seizures, surgeons removed specific structures in the temporal lobe, including the hippocampus. * Following surgery, he displayed severe anterograde amnesia but his intellect remained intact. * Anatomical scans showed a complete absence of the tissue that would otherwise be the hippocampus.
Case Study: Clive Wearing: * Experienced damage from viral encephalitis, leading to high brain temperatures and hypoxia (lack of oxygen) in the hippocampus. * His life consists of a "blinker-like" moment-to-moment consciousness with a memory span of approximately seconds. * He feels as though he is constantly waking up for the first time. He records this in a diary (e.g., : "I am now completely awake for the first time"), though he later denies writing the entries, claiming he was unconscious. * Preserved Abilities: Despite losing his personal history, his intellect is intact, and his procedural memory remains (e.g., he can still play the piano and conduct music). * His emotional recognition remains, illustrated by his profound love for his wife, Deborah, and his reaction to Darius Barington.
Retrograde Amnesia and Cortical Recovery
Definition: The inability to recall information that was acquired before the amnestic event.
Causes: Most commonly associated with traumatic brain injuries (TBI) or concussions. Impact at the frontal cortex can cause transient or long-term damage.
Characteristics: Memories nearest to the time of the event are the most effectively erased. Retrograde amnesia is often accompanied by short-term anterograde amnesia due to global brain damage.
Retrieval Facilitation: Historically, neurosurgeon Walter Penfield demonstrated that stimulating specific cortical areas could evoke or facilitate the retrieval of stored memories.
Alzheimer’s Disease: Pathology, Symptoms, and Progression
Historical Discovery: Named after Doctor Alzheimer, who documented the case of a patient in her exhibiting disorientation, confusion, and memory loss.
Demographic Impact: * Currently affects individuals in the U.S. and over worldwide. * It is a disease of aging; at age , there is a in chance of diagnosis.
Gross Pathology: * Atrophy: General shrinking of the brain. * Ventricle Enlargement: Spaces in the brain containing cerebrospinal fluid expand as tissue is lost. * Cerebral Arterial Sclerosis: The hardening and increased brittleness of brain blood vessels.
Microscopic Pathology: * Amyloid Plaques: Extra-cellular protein structures that are difficult to break apart. * Neurofibrillary Tangles: Intra-cellular "mucking up" of cell function through protein cross-linking.
Staged Memory Loss: * Early Stage: Degeneration of the hippocampus and the basal forebrain (which uses acetylcholine). This results in anterograde amnesia (e.g., losing keys, getting lost). * Later Stage: Proliferation of plaques and tangles to the amygdala and cortex. This leads to retrograde amnesia (e.g., forgetting the names of grandchildren, children, and eventually spouses) and emotional flux.
Risk Factors: * High age is the primary factor. * Genetic factors account for only 4 ext{%} to 8 ext{%} of cases, mostly in young-onset AD. * Head trauma (CTE), Diabetes, Schizophrenia, and hearing loss.
Treatments: * Current drugs (e.g., Memantine) only treat symptoms or slow breakdown of acetylcholine; they do not stop the progression of the disease. * Immunotherapies: Targeted at removing amyloid plaques, though they may only mask existing damage. * Cognitive Reserve: Complex cognitive and physical exercise (at least times a week) can build structural connectivity. Studies on women in a convent showed that those engaging in complex cognitive activities remained asymptomatic despite having AD pathology.
Korsakoff Syndrome: Nutrition and Confabulation
Origin: Documented by Oliver Sacks in The Man Who Mistook His Wife for a Hat.
Cause: Severe thiamine (Vitamin B1) deficiency, typically due to severe malnutrition. It is commonly seen in alcohol use disorders because alcohol interferes with vitamin absorption and provides empty calories.
Pathology: Selective degeneration of the mammillary bodies (part of the thalamus) within the rehearsal circuit.
Symptoms: * Severe anterograde amnesia. * Confabulation: The use of imagination to create stories to fill memory gaps (e.g., a patient imagining a friend named Tom Hickens, a butcher, or a customer to make sense of the current moment). * Temporal Stasis: Patients often believe they are still the age they were when the symptoms began (e.g., a -year-old believing he is ).
Prevention and Treatment: There is no treatment once the cells are gone. Prevention strategies include thiamine-enriched bread and public health initiatives like adding thiamine to beer (e.g., Australians voting to put thiamine in beer).