last updated:

April 28, 2021

[Brain Image]    

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:

Alzheimer's Disease.
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

 IV. The Hippocampus

Amnesia => memory loss


Memory Loss: Patient "H.M." & Damage to the Hippocampus [Wikipedia]

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).

Henry Molaison H.M.

What kind of brain functioning did H.M. show?

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

[Jays & hippocampal
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-Grid cells"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.
Hippocampus-Entorhinal cortext

3. Context: Configural Learning & Binding

V. Striatum: Implicit or Habit Learning (Where Skills and Habits Meet)
(Graybiel & Grafton, 2015)

basal gangliaWe 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,


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