7.2 Brain Regions Involved in Learning & Memory

What was Karl Lashley interested in finding in the brain?

Where memories were stored.

What did Lashley call the location within the cortex where memories were stored?

An “engram” or memory trace.

What did Lashley train rats to do?

Run in a complex maze to reach a food reward.

After the animals learned how to successfully run the maze, what did Lashley do?

Lesion different areas of the rat cortex and then test the rats in the maze again.

What did Lashley find regardless of the location of the lesion in his experiment?

Cortical lesions resulted in decreased ability to remember the location of the food reward and run the maze.

What corresponded to the amount of memory deficit in the animal?

The size of the lesion.

What did not have an effect on memory deficit?

The location of the lesion.

What did Lashley’s findings demonstrate about the engram?

It was widely spread across the cortex.

Explain Lashley’s experiment and what it demonstrated.

He trained rats to run in a maze to reach a food reward. After the rats learned how to run the maze successfully, he lesioned different areas of the cortex. He found that regardless of lesion location, each rat had decreased ability to remember the location of food reward and run the maze. He discovered instead that the size of the lesion led to memory deficits and location did not. This demonstrated that the engram is spread across the cortex

What are the main structures of the medial temporal lobes?

The hippocampus, the entorhinal cortex, the perirhinal cortex, and parahippocampal cortex.

Together, what are the main structures of the medial temporal lobes important in?

Both consolidation and storage of declarative memories.

What does hippocampus mean in Greek?

Seahorse.

Why was the hippocampus named hippocampus?

Based on its morphology.

The hippocampus is one of the critical structures of what system?

The limbic system.

What is the limbic system?

A series of subcortical brain structures that are involved in several different complex behaviors, such as emotions and memory.

Who first described hippocampal synaptic connectivity?

Ramon y Cajal.

What is hippocampal synaptic connectivity sometimes called?

The trisynaptic circuit.

Explain the trisynaptic circuit

1. Perforant pathway: axonal outputs of layers 2 and 3 of entorhinal cortex synapse onto granule cells of the dentate gyrus. | 2. Mossy fibers: granule cells send axons to pyramidal cells of the CA3 region of the HPC. | 3. Schaffer collaterals: CA3 pyramidal cells send axonal projections to the CA1 region, which then projects outputs back to layers 5 and 6 of the entorhinal cortex.

What is the white matter signaling tract called that carries inputs into the hippocampus?

The perforant pathway.

What are the axons of granule cells called?

Mossy fibers

What are the axonal projections from CA3 called?

Schaffer collaterals.

Where do the outputs of the hippocampus project?

To layer 5 and 6 of the entorhinal cortex.

What type of neurotransmission characterizes the three main neuronal projections of the trisynaptic circuit?

glutamatergic.

What neurotransmitters regulate and modulate the trisynaptic circuit?

GABA, acetylcholine, norepinephrine, and serotonin.

What type of memories is the hippocampus involved in?

Spatial and declarative memories.

What are spatial memories?

Memories involved in navigation of surroundings and the creation of a mental map of the world.

What are examples of spatial memories?

When a person enters a new building for the first time or when searching for a new classroom.

Is the volume of the hippocampus a reliable indicator of the strength of a healthy person’s spatial memory?

No

What does injury to the hippocampus cause?

Deficits in spatial memory.

What test is regularly used in rodents to test spatial memory behaviorally?

The Morris water maze.

Explain the Morris water maze.

A platform is hidden somewhere in an opaque pool with environmental cues on the surface. The time it takes for the rat to swim to the platform is recorded. Over time, the subject learns the platform is near certain navigational cues, and the latency to find it decreases. Rodents with a removed or inactive HPC perform poorly.

What fills the pool in the Morris water maze?

An opaque liquid.

What happens over time as the animals learn the Morris water maze?

The animals learn that the platform is located near certain navigational cues.

What happens on future trials after the animals learn the Morris water maze?

The animals spend more time near those cues, and the latency to find the platform decreases.

How do rodents perform in the Morris water maze when the HPC is surgically removed or inactivated?

They perform poorly in the Morris water maze.

Based on the deficits seen in Patient HM and other experimental manipulations of the HPC, what has been concluded about the HPC?

It is strongly implicated in the process of declarative memories and spatial navigation.

What memory functions, as seen in HM, are independent of HPC function?

Procedural and working memory

Where is the amygdala found?

Part of the limbic system. Located in the medial temporal lobe adjacent to the HPC.

What does amygdala mean in Greek?

Almond.

What are the two broad divisions of the amygdala?

The basolateral amygdala (BLA) and the central nucleus of the amygdala (CeA).

What does the basolateral amygdala contribute to?

fear memories and reward processing.

What does the central nucleus of the amygdala contribute to?

The physiological response in emotions and the perception of emotion.

What is the amygdala strongly involved with?

The formation and storage of emotional memories.

What are emotional memories?

Memories or associations that have a strong emotional connection.

What emotional states are represented in the amygdala?

Positive and negative

What is the foot-shock paradigm?

A non-human test of emotional memory

The foot-shock paradigm is a form of what?

Fear conditioning.

What does the foot-shock paradigm involve?

A rodent is put into a room with metal rods as the floor. When a combination of sound and light cues is presented to the animal, a foot shock occurs shortly after. When the sound and light are presented again, they exhibit freezing behavior.

If the animal learns that the cues are associated with the negative painful memory, what behavior does it exhibit?

freezing after exposure to the cues.

What effect do amygdala lesions have in the foot-shock paradigm?

Amygdala lesions prevent the animal from freezing.

What effect do hippocampal lesions have in the foot-shock paradigm?

No effect on emotional learning

What effect does changing cellular signaling in the amygdala have?

alters the learning of fear conditioning.

The foot-shock paradigm is often used as a non-human model of what disorder?

Post-traumatic stress disorder.

Structures of the inferotemporal cortex (IT) are part of what?

The ventral stream (“what”) of visual perception.

What does the inferotemporal cortex store?

Some components of visual memory.

What part of the inferotemporal cortex is involved in facial recognition?

The fusiform gyrus.

What disorder affects the fusiform gyrus?

Prosopagnosia.

What is prosopagnosia?

Where a person can perceive different parts of another person’s face, but has difficulty putting the whole picture together or matching those features to a specific person.

Why is facial recognition a memory-related process?

In order to be accurate, there must be some memory that allows for a person to match facial features with someone they have seen before.

Where is the PPA found?

In the IT

What does the parahippocampal place area (PPA) contribute to?

Visual memories associated with locations and environmental scenes.

When does activity of the PPA increase?

When people view place-related images.

What are examples of place-related images?

Scenic landscapes like mountains, man-made structures like campus buildings, or the interiors of rooms, both furnished and completely empty.

What stimuli do not increase the activity of the PPA?

Viewing faces or objects

What is the prefrontal cortex involved in?

Higher-order decision making and personality.

In the context of memory, what are neural circuits in the PFC important for?

Short-term and working memory.

How did patients with injuries to their PFC after stroke, tumor, and aneurysm perform on working memory tasks?

Worse, including tasks such as the digit span test.

What disorder is characterized by a degradation of the frontal lobe?

Frontotemporal dementia.

What memory difficulty is common in people with frontotemporal dementia?

working memory.

What are the PFC-hippocampus circuits likely involved in?

The formation of hippocampal-dependent memories.

The striatum is a structure of what?

The basal ganglia.

What do the basal ganglia contribute to?

Behaviors such as motor activity and procedural memories.

What type of memories does the striatum likely hold?

Memories involved in habits.

How do habitual behaviors help us?

To preserve cognitive bandwidth, reducing the “mental energy” that is used during repetitive task performance.

What is the downside of habits?

Heavily relying on habits limits behavioral flexibility, causing a person to repeat an action that worked previously without evaluating new, present circumstances.

What does the cerebellum generally help with?

Motor functions.

What type of memories is the cerebellum involved in?

Procedural memories, particularly the performance of motor abilities

Learning new skills likely requires what in the cerebellum?

Changes in the circuit strength of cerebellar neurons

What brain region plays a role in positive emotional memories?

The orbitofrontal cortex.

What cortices are important for memories related to the specific stimuli processed in those areas?

Sensory cortices.