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Posts Tagged ‘Spatial memory’

How does short-term memory work in relation to long-term memory? Are short-term daily memories somehow transferred to long-term storage while we sleep?


Alison Preston, an assistant professor at the University of Texas at Austin’s Center for Learning and Memory, recalls and offers an answer for this question.

A short-term memory’s conversion to long-term memory requires the passage of time, which allows it to become resistant to interference from competing stimuli or disrupting factors such as injury or disease. This time-dependent process of stabilization, whereby our experiences achieve a permanent record in our memory, is referred to as “consolidation.”

Memory consolidation can occur at many organizational levels in the brain. Cellular and molecular changes typically take place within the first minutes or hours of learning and result in structural and functional changes to neurons (nerve cells) or sets of neurons. Systems-level consolidation, involving the reorganization of brain networks that handle the processing of individual memories, may then happen, but on a much slower time frame that can take several days or years.

Memory does not refer to a single aspect of our experience but rather encompasses a myriad of learned information, such as knowing the identity of the 16th president of the United States, what we had for dinner last Tuesday or how to drive a car. The processes and brain regions involved in consolidation may vary depending on the particular characteristics of the memory to be formed.

Let’s consider the consolidation process that affects the category of declarative memory—that of general facts and specific events. This type of memory relies on the function of a brain region called the hippocampus and other surrounding medial temporal lobe structures. At the cellular level, memory is expressed as changes to the structure and function of neurons. For example, new synapses—the connections between cells through which they exchange information—can form to allow for communication between new networks of cells. Alternately, existing synapses can be strengthened to allow for increased sensitivity in the communication between two neurons.

Consolidating such synaptic changes requires the synthesis of new RNA and proteins in the hippocampus, which transform temporary alterations in synaptic transmission into persistent modifications of synaptic architecture. For example, blocking protein synthesis in the brains of mice does not affect the short-term memory or recall of newly learned spatial environments in hippocampal neurons. Inhibiting protein synthesis, however, does abolish the formation of new long-term representations of space in hippocampal neurons, thus impairing the consolidation of spatial memories.

Over time, the brain systems that support individual, declarative memories also change as a result of systems-level consolidation processes. Initially, the hippocampus works in concert with sensory processing regions distributed in the neocortex (the outermost layer of the brain) to form the new memories. Within the neocortex, representations of the elements that constitute an event in our life are distributed across multiple brain regions according to their content. For example, visual information is processed by primary visual cortex in the occipital lobe at the rear of the brain, while auditory information is processed by primary auditory cortex located in the temporal lobes, which lie on the side of the brain.

When a memory is initially formed, the hippocampus rapidly associates this distributed information into a single memory, thus acting as an index to representations in the sensory processing regions. As time passes, cellular and molecular changes allow for the strengthening of direct connections between neocortical regions, enabling the memory of an event to be accessed independently of the hippocampus. Damage to the hippocampus by injury or neurodegenerative disorder (Alzheimer’s disease, for instance) produces anterograde amnesia—the inability to form new declarative memories—because the hippocampus is no longer able to connect mnemonic information distributed in the neocortex before the data has been consolidated. Interestingly, such a disruption does not impair memory for facts and events that have already been consolidated. Thus, an amnesiac with hippocampal damage would not be able to learn the names of current presidential candidates but would be able to recall the identity 16th US president (Abraham Lincoln, of course!).

The role of sleep in memory consolidation is an ancient question dating back to the Roman rhetorician Quintilian in the first century A.D. Much research in the past decade has been dedicated to better understanding the interaction between sleep and memory. Yet little is understood.

At the molecular level, gene expression responsible for protein synthesis is increased during sleep in rats exposed to enriched environments, suggesting memory consolidation processes are enhanced, or may essentially rely, on sleep. Further, patterns of activity observed in rats during spatial learning are replayed in hippocampal neurons during subsequent sleep, further suggesting that learning may continue in sleep.

In humans, recent studies have demonstrated the benefits of sleep on declarative memory performance, thus giving a neurological basis to the old adage, “sleep on it.” A night of sleep reportedly enhances memory for associations between word pairs. Similar overnight improvements on virtual navigation tasks have been observed, which correlate with hippocampal activation during sleep. Sleep deprivation, on the other hand, is known to produce deficits in hippocampal activation during declarative memory formation, resulting in poor subsequent retention. Thus, the absence of prior sleep compromises our capacity for committing new experiences to memory. These initial findings suggest an important, if not essential, role for sleep in the consolidation of newly formed memories.

Story Source:

The above story is reprinted from materials provided by ScientificAmerican magazine.

Why Do We Think Better after We Exercise?


Why is it that we seem to think better when we walk or exercise?

Justin Rhodes, an associate professor of psychology at the University of Illinois at Urbana-Champaign, responds:

After being cooped up inside all day, your afternoon stroll may leave you feeling clearheaded. This sensation is not just in your mind. A growing body of evidence suggests we think and learn better when we walk or do another form of exercise. The reason for this phenomenon, however, is not completely understood.

Part of the reason exercise enhances cognition has to do with blood flow. Research shows that when we exercise, blood pressure and blood flow increase everywhere in the body, including the brain. More blood means more energy and oxygen, which makes our brain perform better.

Another explanation for why working up a sweat enhances our mental capacity is that the hippocampus, a part of the brain critical for learning and memory, is highly active during exercise. When the neurons in this structure rev up, research shows that our cognitive function improves. For instance, studies in mice have revealed that running enhances spatial learning. Other recent work indicates that aerobic exercise can actually reverse hippocampal shrinkage, which occurs naturally with age, and consequently boost memory in older adults. Yet another study found that students who exercise perform better on tests than their less athletic peers.

The big question of why we evolved to get a mental boost from a trip to the gym, however, remains unanswered. When our ancestors worked up a sweat, they were probably fleeing a predator or chasing their next meal. During such emergencies, extra blood flow to the brain could have helped them react quickly and cleverly to an impending threat or kill prey that was critical to their survival.

So if you are having a mental block, go for a jog or hike. The exercise might help pull you out of your funk.

Story Source:

The above story is reprinted from materials provided by ScientificAmerican magazine.