Posts Tagged ‘O’Keefe’

The Hippocampus

January 22, 2020

This post is based on text from Wayfinding, a book by M.R. O’Connor. The hippocampus was discovered by mistake. In the early 1970s John O’Keefe, a young American scientist, used the wrong coordinates and instead of placing micro electrodes in a rat’s somatosensory thalamus, he inserted the micro electrodes into the rat’s hippocampus. As the single cell O’Keefe was recording began to fire, its pattern struck him as unusual. The cell’s activity was strongly correlated with the rat’s locomotion. O’Keefe began recording single hippocampal cells of rats while they were eating, grooming, and exploring.

After months of recording, O’Keefe began to suspect that the activity of these cells didn’t depend so much on what the animal was doing or why it was doing it, but had something to do with where it was doing it. It didn’t matter which direction the rat was facing, or whether rewards were taken away or changed. The only stimulus that seemed to matter to these cells was the rat’s location. Instead of responding to the changes in stimuli, the cells were signaling the abstract concept of space. O’Keefe called them place cells.

The psychologist Tolman published a paper in 1948 in Psychological Review titled “Cognitive Maps in Rats and Men.” At the end of the paper he made the following conjectures. Was it possible that many people’s social maladjustments could be interpreted as the result of having too narrow and limited cognitive maps? In one example Tolman wrote about the tendency for individuals to focus their aggression on outside groups. He wrote that poor southern whites displace they frustrations with landlords, the economy, and northerners onto black American. Americans as a whole displace their aggression into Russians and vice versa. He wrote,

“My only answer is to preach again the virtues of reason—of, that is, broad cognitive maps…Only then can have children learn to look before and after, to see that there are often round-about and safer paths to their quite proper goals—learn that is, to realize that the well-beings of White and Negro, of Catholic and Protestant, of Christian and of Jew, of American and Russian (and even of males and females) are mutually interdependent. We dare not let ourselves or others become so over-emotional, so hungry, so ill-clad, and so over motivated that only narrow strip-maps will be developed.”

Remember that this was published in 1948.

Research has shown that the richness and complexity of an environment influences the quantity of neurons in the hippocampus. In 1997, researchers at the Salk Institute found that mice exploring enriched environments—paper tubes, nesting material, running wheels, and rearrangeable plastic tubes—had forty thousand more neurons than a control group. These additional neurons resulted in an increase in hippocamplal volume of 15% in the mice and significant improvements on spatial learning tests. The researchers concluded that a combination of increased neurons, synapses, vasculature, and dendrites led to the animals’ enhanced performance.

Eichenbaum believed that the hippocampus is capable not only of organizing physical space, but of creating “temporally structured experiences” into representations of moments in time. Eichenbaum has come to understand the hippocampus as the “grand organizer” of the brain. “It’s organizing and integrating all these bits and pieces of information in a contextual framework. It does create a map, I’m all for the cognitive map in the original sense that it’s a map where you put the stuff to remember where they are in relationship to each other. That is a specific, limited, concise sense of moving in geographic space . The other sense is this abstract term, how did I navigate to graduate school? What’s the path to the presidency?”

The most famous case of amnesia in the scientific literature is H.M., an epileptic who in the 1950s at the age of 27 had part of his temporal lobes removed, which included the hippocampus (actually we have two of these, one in each hemisphere of the brain). This caused him to lose his ability to acquire and recollect memories. Although he could recall the past, he could not store the present so he could recall any new information.

HM, not be be confused with H.M. had similar experiences with his mother when she was suffering from dementia. She reached a point when he visited her, and she needed to be taken to the restroom, when she returned she would not remember my visit and would think that I had just arrived. At this point HM realized that the dementia had destroyed her two hippocampi. This was a very sad time.

31st Meeting of the Association for Psychological Science Pt. 2

June 3, 2019

A definite highlight of the meeting was lecture by Lynn Nadel titled, Taking James Seriously: The Implications of Multiple Memory Systems. The James referred to in the title is William James, the father of American Psychology. James wrote about multiple memory systems, a primary and a secondary memory, which today are referred to as short term and long term memory. He made a distinction between habits and memory.

James passed away long before the emergence of neuroscience. The hippocampus plays an important role in the processing of memories. There was a famous epileptic patient referred to as HM who had large portions of his temporal lobes removed. A hippocampus is located in each one of those lobes. Although his previous memories remained intact, not only each new day, but each new hour was a new experience for HM. And these experiences would not be remembered.

There is a distinction between episodic memory, which holds the memories of our daily experiences is processed in the hippocampus, and semantic memory, which holds our general knowledge of the world, is resident in our neocortex.

The hippocampus is also critical to navigation. The neuroscientist O’Keefe identified place cells in the hippocampus. These place cells identify spatial locations where the organism travels. Learning to navigate entails strengthening these place cells and learning to follow them to desired locations.

In most species, the hippocampus matures postnatally. This has important consequences for memory and cognitive development. Dr. Nadel asks what does it mean to start life with a developing, but not yet functioning hippocampus, perhaps uniquely susceptible to impacts of experience early in life. In humans it takes 18-24 months for the hippocampus to emerge, and it takes 10-12 years for it to become fully functional.

Dr. Nadel speculates that phobias can develop before the hippocampus emerges. This late emergence of the hippocampus explains infantile amnesia and delayed exploration and place learning. Everything we learn very early in life is context free. The individual has no understanding of why she has certain fears, as the cause of the fear was not stored in memory. As for the 10-12 years for the hippocampus, an extremely important structure, to become fully functional, it might result in shortcomings in learning and interpersonal interactions.