April 28, 2021
PSY 340 Brain and Behavior
Class 33: The Hippocampus and Striatum
Prevalence Data on KS and Alzheimer's Disease
United States population in 2020 was 331 million people
Korsakoff's Syndrome. I was asked in class about the prevalence of Korsakoff's Syndrome, a fact that I did not readily know other than the fact it was rare. Arts et al. (2017) note that there is very little data about the prevalence and what data there is show a range of values:
- 48 per 100,000 in The Hague, The Netherlands (1987 study) ===> equivalent to ca. 159K total cases in US in 2020
- 30 per 100,000 in North-Holland, The Netherlands (1992 study)
- 5 per 100,000 per year in Glasgow, Scotland (1990-1995) ====> equivalent to ca. 16.5K total cases in US in 2020
- No other prevalence rates appear to be available
Normal Aging ---15-20%---> Mild Cognitive Impairment (MCI) ---10-20% ---> AD
In 2020 there were roughly 55 million Americans 65 years of age or older
- 6.2 million Americans 65 years old+ in 2021 have AD
- 11.5% of Americans 65 years old+ in 2021 have AD
- Projected 12.7 million wlll have AD by 2050
IV. The Hippocampus
Amnesia => memory loss
Memory Loss: Patient "H.M." & Damage to the Hippocampus
Patient "H.M." was born in 1929. He was knocked down by a bike when he was 7 and was unconscious for several minutes. He soon began having minor seizures. When we was 16-years-old (1942), he had his first major seizure. By the time he was 27 (1953), H.M. was suffering 10 minor seizures every day and a major seizure weekly. That year he underwent a major brain operation: bilateral medial temporal lobe resection (= removal of the hippocampus and nearby tissue structures). By age 28 (1955), it became clear that H.M. had a pervasive problem with his memory. He was referred him to Dr. Brenda Milner, a neuropsychologist, in Montreal. Beginning in 1955, H.M. has been the subject of many studies.
H.M., whose real name we now know was Henry Gustav Molaison, died in Windsor Locks, CT on December 2, 2008 (Carey, 2008).
What kind of brain functioning did H.M. show?
- No effect on intellect & language functions. I.Q. slightly higher in the years immediately after operation.
- Personality was relatively the same except for "emotional placidity" (= no complaints; no requests even for food)
- Good short-term memory, i.e., for new items up to about 5-10 minutes after the experience.
- Massive anterograde amnesia (loss of memories of new events since brain damage) and moderate retrograde amnesia (loss of memories of events before brain damage).
- Little new learning of declarative memories, i.e., facts, and no new memories of events, e.g., what happened in the world since 1955. He did not learn new words which came into English since his operation. However he did respond with some new learning
- Prompt: "Elvis" • HM's response: "Presley"
- Prompt: "Fidel" • HM's response: "Castro"
- Prompt: "Martin Luther" • HM's response: "King"
- Also, when he examined pictures of past events including those of his family, he recognized names & some places, but could not recall the events pictures showed, thus, severe impairment in episodic (personal) memories. In fact, he had he had very little memory of any specific events of his earlier life (exception: he remembered that he once flew in a two-seater airplane as a child which was true).
- Intact procedural memory, i.e., learning how to do something new.
Explicit memory: recall of information which one knows is in memory
Implicit memory: influence of recent experience on behavior even though one doesn't recognize memory is being used.
- H.M. showed poor new explicit memory, but nearly normal implicit memory.
What does the Hippocampus Do? Theories of Hippocampal Functioning
1. Declarative Explicit Memory: Bilateral damage in humans leads to impairment in storing any new memories for facts (declarative memories) and events (episodic memories). The basal ganglia (see below) seem to be more important for new procedural memories.
2. Spatial Memory
- London taxi cab drivers have "the Knowledge" = a detailed memory for every single street in London and how to go from one place to another by the quickest route. Studies show high levels of activation via PET scans for spatial related questions (e.g., What is the shortest route from the Tate Museum to Buckingham Palace?). Further, drivers have larger posterior hippocampi (plural of hippocampus) than normal.
- Humans with damage to the hippocampus do poorly on tests of spatial memory
- Bird species with good spatial memory (e.g., Clark's nutcracker which finds hidden seeds during winter) have larger hippocampi relative to rest of brain than birds who have poor spatial memory.
Brain's "navigational grid & place cell" system discovered by 2014 Nobel Laureates John O'Keefe (USA/UK) and May-Britt Moser & Edvard Moser (Norway)
"Place Cells" • John O'Keefe discovered in the brain of rats a spatial map reference system associated with the hippocampus. When rats in an enclosed space moved to different places in that space, specific cells in the hippocampus fired. These creates a mental map of the space. These cells appear to have a memory function as well and allow an animal to navigate environments later on in which they had previously found themselves.
"Grid Cells" • May-Britt & Edvard Moser found that the entorhinal cortex (the area just behind the hippocampus) is highly connected to the hippocampus. They discovered in the entorhinal cortex a special type of cell called a "grid cell" which (1) fires as rat moves around a spacial environment and (2) are arranged in a hexagonal patterns. These cells not only provide a knowledge of place but also of the direction of the animal's head as well. This brain area appears to allow an animal to calculate distance between itself and different places within the environment.
3. Context: Configural Learning & Binding
- Recent work suggests a major role for the hippocampus in binding together all the elements of declarative memory, complex spatial memories, and single-event configurational memories.
- Memory is a collection of different pieces of experience: sights, sounds, smells, tastes, etc. These are probably stored in diverse parts of the brain and require some sort of map to bring them back together again. The hippocampus may provide that map via connections to the rest of the forebrain
V. Striatum: Implicit or Habit Learning (Where Skills and Habits Meet)
(Graybiel & Grafton, 2015)
We learn many memories of experiences after only a single event. But, consider how you tend to learn gradually what to expect of another person's behavioral tendencies, e.g., how a basketball player will move offensively, how your mother will unpack the weekend's shopping from Wegman's, or the various cues your teacher might give about what he or she expects in class. All of these relate to the notion of implicit or habit learning.
Gradual implicit or habit learning appears to depend upon a diverse set of nuclei in the subsurface of the brain called the basal ganglia. These include the striatum (i.e., putamen and caudate nucleus) in particular as well as the globus pallidus, substantia nigra, and subthalamic nuclei. These bodies use dopamine as a neurotransmitter and have previously been shown to be centrally involved in movement.
The striatum appears to be mostly involved in what can be termed "reinforcement-level learning" - that is,
- Gradual learning over multiple trials
- Learning habits and skills
- Learning requires prompt feedback (= reward or punishment is clear)
- Learning is implicit, that is, what is learned is not put into words, but into actions
- If the striatum is damaged, the ability to learn new skills or habits is impaired and previously learned skills/habits are often impaired as well
Arts, N. J. M., Walvoort, S. J. W., & Kessels, R. P. C. (2017). Korsakoff’s syndrome: A critical review. Neuropsychiatric Disease and Treatment, 13, 2875-2890. https://doi.org/10.2147/NDT.S130078
Carey, B. (2008, December 4). H.M., an unforgettable amnesiac, dies at 82. New York Times. [Obituary]
Graybiel, A. M., & Grafton, S. T. (2015) The striatum: Where skills and habits meet. Cold Spring Harbor Perspectives in Biology, 7, a021691.
This page was first posted April 17, 2005