Memory and the Brain

Neural Correlates of Memory Consolidation

The hippocampus, amygdala, and cerebellum play important roles in the consolidation and manipulation of memory.

Learning Objectives

Analyze the role each brain structure involved in memory formation and consolidation

Key Takeaways

Key Points

  • Memory consolidation  is a category of processes that stabilize a memory trace after its initial acquisition.
  • The hippocampus is essential for the consolidation of both short-term and long-term memories. Damage to this area of the brain can render a person incapable of making new memories and may even affect older memories that have not been fully consolidated.
  • The amygdala has been associated with enhanced retention of memory. Because of this, it is thought to modulate memory consolidation. The effect is most pronounced in emotionally charged events.
  • The cerebellum is associated with creativity and innovation. It is theorized that all processes of working memory are adaptively modeled by the cerebellum.

Key Terms

  • declarative memory: The type of long-term memory that stores facts and events; also known as conscious or explicit memory.
  • encoding: The process of converting information into a construct that can be stored within the brain.
  • consolidation: The act or process of turning short-term memories into more permanent, long-term memories.

Memory consolidation is a category of processes that stabilize a memory trace after its initial acquisition. Like encoding, consolidation affects how well a memory will be remembered after it is stored: if it is encoded and consolidated well, the memory will be easily retrieved in full detail, but if encoding or consolidation is neglected, the memory will not be retrieved or may not be accurate.

Consolidation occurs through communication between several parts of the brain, including the hippocampus, the amygdala, and the cerebellum.

The Hippocampus

While psychologists and neuroscientists debate the exact role of the hippocampus, they generally agree that it plays an essential role in both the formation of new memories about experienced events and declarative memory (which handles facts and knowledge rather than motor skills). The hippocampus is critical to the formation of memories of events and facts.

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The hippocampus: The hippocampus is integral in consolidating memories from short-term to long-term memory.

Information regarding an event is not instantaneously stored in long-term memory. Instead, sensory details from the event are slowly assimilated into long-term storage over time through the process of consolidation. Some evidence supports the idea that, although these forms of memory often last a lifetime, the hippocampus ceases to play a crucial role in the retention of memory after the period of consolidation.

Damage to the hippocampus usually results in difficulties forming new memories, or anterograde amnesia, and normally also brings about problems accessing memories that were created prior to the damage, or retrograde amnesia. A famous case study that made this theory plausible is the story of a patient known as HM: After his hippocampus was removed in an effort to cure his epilepsy, he lost the ability to form memories. People with damage to the hippocampus may still be able to learn new skills, however, because those types of memory are non-declarative. Damage may not affect much older memories. All this contributes to the idea that the hippocampus may not be crucial in memory retention in the post-consolidation stages.

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The amygdala: The amygdala is involved in enhancing the consolidation of emotional memories.

The Amygdala

The amygdala is involved in memory consolidation—specifically, in how consolidation is modulated. “Modulation” refers to the strength with which a memory is consolidated. In particular, it appears that emotional arousal following an event influences the strength of the subsequent memory. Greater emotional arousal following learning enhances a person’s retention of that stimulus.

The amygdala is involved in mediating the effects of emotional arousal on the strength of the memory of an event. Even if the amygdala is damaged, memories can still be encoded. The amygdala is most helpful in enhancing the memories of emotionally charged events, such as recalling all of the details on a day when you experienced a traumatic accident.

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The cerebellum: A vertical cross-section of the human cerebellum, showing the folding pattern of the cortex, and interior structures.

The Cerebellum

The cerebellum plays a role in the learning of procedural memory (i.e., routine, “practiced” skills), and motor learning, such as skills requiring coordination and fine motor control. Playing a musical instrument, driving a car, and riding a bike are examples of skills requiring procedural memory. The cerebellum is more generally involved in motor learning, and damage to it can result in problems with movement; specifically, it is thought to coordinate the timing and accuracy of movements, and to make long-term changes (learning) to improve these skills. A person with hippocampal damage might still be able to remember how to play the piano but not remember facts about their life. But a person with damage to their cerebellum would have the opposite problem: they would remember their declarative memories, but would have trouble with procedural memories like playing the piano.

Neural Correlates of Memory Storage

Although the physical location of memory remains relatively unknown, it is thought to be distributed in neural networks throughout the brain.

Learning Objectives

Discuss the physical characteristics of memory storage

Key Takeaways

Key Points

  • It is theorized that memories are stored in neural networks in various parts of the brain associated with different types of memory, including short-term memory, sensory memory, and long-term memory.
  • Memory traces, or engrams, are physical neural changes associated with memories. Scientists have gained knowledge about these neuronal codes from studies on neuroplasticity.
  • Encoding of episodic memory involves lasting changes in molecular structures, which alter communication between neurons. Recent functional-imaging studies have detected working-memory signals in the medial temporal lobe and the prefrontal cortex.
  • Both the frontal lobe and prefrontal cortex are associated with long- and short-term memory, suggesting a strong link between these two types of memory.
  • The hippocampus is integral in consolidating memories but does not seem to store memories itself.

Key Terms

  • engram: A postulated physical or biochemical change in neural tissue that represents a memory; a memory trace.
  • neuroplasticity: The state or quality of the brain that allows it to adapt to experience through physical changes in connections.

Many areas of the brain have been associated with the processes of memory storage. Lesion studies and case studies of individuals with brain injuries have allowed scientists to determine which areas of the brain are most associated with which kinds of memory. However, the actual physical location of memories remains relatively unknown. It is theorized that memories are stored in neural networks in various parts of the brain associated with different types of memory, including short-term memory, sensory memory, and long-term memory. Keep in mind, however, that it is not sufficient to describe memory as solely dependent on specific brain regions, although there are areas and pathways that have been shown to be related to certain functions.

Memory Traces

Memory traces, or engrams, are the physical neural changes associated with memory storage. The big question of how information and mental experiences are coded and represented in the brain remains unanswered. However, scientists have gained much knowledge about neuronal codes from studies on neuroplasticity, the brain’s capacity to change its neural connections. Most of this research has been focused on simple learning and does not clearly describe changes involved in more complex examples of memory.

Encoding of working memory involves the activation of individual neurons induced by sensory input. These electric spikes continue even after the sensation stops. Encoding of episodic memory (i.e., memories of experiences) involves lasting changes in molecular structures that alter communication between neurons. Recent functional-magnetic-resonance-imaging (fMRI) studies detected working memory signals in the medial temporal lobe and the prefrontal cortex. These areas are also associated with long-term memory, suggesting a strong relationship between working memory and long-term memory.

Brain Areas Associated with Memory

Imaging research and lesion studies have led scientists to conclude that certain areas of the brain may be more specialized for collecting, processing, and encoding specific types of memories. Activity in different lobes of the cerebral cortex have been linked to the formation of memories.

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Lobes of the cerebral cortex: While memory is created and stored throughout the brain, some regions have been shown to be associated with specific types of memory. The temporal lobe is important for sensory memory, while the frontal lobe is associated with both short- and long-term memory.

Sensory Memory

The temporal and occipital lobes are associated with sensation and are thus involved in sensory memory. Sensory memory is the briefest form of memory, with no storage capability. Instead, it is a temporary “holding cell” for sensory information, capable of holding information for seconds at most before either passing it to short-term memory or letting it disappear.

Short-Term Memory

Short-term memory is supported by brief patterns of neural communication that are dependent on regions of the prefrontal cortex, frontal lobe, and parietal lobe. The hippocampus is essential for the consolidation of information from short-term to long-term memory; however, it does not seem to store information itself, adding mystery to the question of where memories are stored. The hippocampus receives input from different parts of the cortex and sends output to various areas of the brain. The hippocampus may be involved in changing neural connections for at least three months after information is initially processed. This area is believed to be important for spatial and declarative (i.e., fact-based) memory as well.

Long-Term Memory

Long-term memory is maintained by stable and permanent changes in neural connections spread throughout the brain. The processes of consolidating and storing long-term memories have been particularly associated with the prefrontal cortex, cerebrum, frontal lobe, and medial temporal lobe. However, the permanent storage of long-term memories after consolidation and encoding appears to depend upon the connections between neurons, with more deeply processed memories having stronger connections.