Chapter 12

     For a long time, scientists thought that all memory was stored in one way. There were many theories, including that each individual neuron held a memory. But as more research was done on memory, including on people with amnesia caused by brain damage, it became clear that different kinds of memories are stored in different ways.

    First, an individual memory is not necessarily stored in one place. Memories often include different information, such as images, language, smells, and emotions, and this kind of information is handled by different cortices and parts of the brain. 

    Working memory, a better term for short-term memory, is information that we hold on to while we're using it. When we try to hold on to information in this way, there will be bursts of gamma oscillations in the cells related to learning while information is being presented, then staggered bursts in the different areas of cells related to the information while it’s being stored but not in use. When it’s needed again, the bursts will become more frequent again.

    While many areas of the brain are involved in memory, two key ones are the hippocampus and the striatum. The hippocampus seems to be responsible for storing and reassembling episodic memories, meaning events that have happened to us that come with a lot of context. These memories come with a lot of sensory detail, which the hippocampus collects from around the brain when we recall it. The hippocampus is also known to have "place cells," which help with spatial memory, such as keeping us oriented in a maze, and "time cells," which help us similarly keep track of the passage of time and order of events. This may be why the hippocampus is so involved in episodic memories, as locations and sequence of events are so important to recalling events.

    The striatum is a name for two parts of the basal ganglia, the caudate nucleus and the putamen. It’s responsible for gradual, probabilistic learning. Some examples are knowing that a gray sky and wind signal possible rain, or that bright sunlight doesn’t guarantee it’s warm. Sometimes it's more complicated, such as learning what kinds of TV shows a friend likes, and knowing what they might be interested in in the future. The striatum is also responsible for learning habits.

    A couple of other regions with important roles in memory are the parietal lobe and the anterior temporal cortex. The parietal lobe is important to elaborating on a memory and putting pieces together. Individuals with parietal lobe damage can answer questions about the who, what, where, when, why, how, etc. but will not be able to share all of these details without being prompted for each piece. 

    The anterior temporal cortex is responsible for a lot of semantic memory, like a database of factual information. People with damage to this part of their brain might forget facts like the typical color of a tomato or kinds of animals they don’t see every day.

Ultimately, when it comes to memories, there's a division of labor between the hippocampus, the striatum, and other areas of the brain like the cerebral cortex. But most tasks require multiple systems. One might remember a specific day where the weather looked sunny but then it rained, and the details of how it felt to be soaked through or attend a meeting with wet clothing. The details of the episodic information here might be handled by the hippocampus. But in telling the story to another person, the parietal lobe would be involved in putting the details back together. And the striatum might be involved in noting that fair skies don't necessarily stick around all day, so that next time the weather looks nice enough, the person might decide to grab an umbrella just in case.

    Our final chapter reading is about cognitive functions, including making decisions. Decision-making often relies on different types of memory, from factual information we've learned, to observations we've made over time that help us understand probabilities, to events that have occurred in our lives, particularly emotional ones. What we've learned and what has happened to us often has a powerful impact on the way we think about ourselves and how we choose to live our lives, to the point where people often get "stuck" in patterns of behavior. I'll be curious to see how regions like the hippocampus and the striatum are involved in cognition and decision-making.