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I've read that in an experiment, a pair of stimulating electrodes were inserted into a blind man's visual cortex, and upon passing electricity, the phosphene phenomenon was produced. Is it the same with memory? Can each and every memory, of an individual be recalled by a similar method? And if so, in which region of the brain will the stimulating electrodes be inserted?
There have been quite a few studies on stimulating the brain with electrical pulses and it has been found to be successful too. Three papers of particular interest I found were:
1) In a study titled "Explaining How Brain Stimulation Can Evoke Memories", it was found that electrical stimulation in the temporal neocortex can cause neurosurgical patients to spontaneously experience memory retrieval. The subject's brain in the study when stimulated enabled him to recollect memories from the time that he was in high school. They concluded that there are patches of neurons encoding memories for differnt periods (in this case the high school). (reference)
2) In the second study titled "Memory Enhancement and Deep-Brain Stimulation of the Entorhinal Area", it was observed that
entorhinal stimulation applied while subjects learned the locations of landmarks enhanced their subsequent memory of these locations: and the subjects reached these landmarks more quickly and by shorter routes, as compared with locations learned without stimulation. (reference)
3) In a third study titled "Stimulation of Entorhinal Cortex Promotes Adult Neurogenesis and Facilitates Spatial Memory", it was found that stimulating a specific region of the brain leads to the production of new brain cells that enhance memory. (reference)
In two on these studies, memory is enhanced by stimulation to the entorhinal cortex and in the first study the neocortex was stimulated. So, in a broad sense the cerebral cortex is generally used for these studies.
This is a continuous field of research as a treatment to diseases like Alzheimers (reference).
Gray-Brodman-Entorhinal Cortex (Wikipedia)
Neocortex location (reference)
How the olfactory brain affects memory
How sensory perception in the brain affects learning and memory processes is far from fully understood. Two neuroscientists of Ruhr-Universität Bochum (RUB) have discovered a new aspect of how the processing of odours impacts memory centres. They showed that the piriform cortex -- a part of the olfactory brain -- has a direct influence on information storage in our most important memory structure, the hippocampus. Dr. Christina Strauch and Professor Denise Manahan-Vaughan report about their findings in the online edition of the magazine Cerebral Cortex on 9 April 2019.
Electric impulses simulate odours
To find out how odours affect memory formation, the researchers triggered an artificial perception of an odour in the brains of rats. To do this, they stimulated the piriform cortex with electrical impulses. "We were very surprised to see that the hippocampus directly responds to stimulation of the piriform cortex," remarked Christina Strauch.
The hippocampus uses sensory information to create complex memories. The basis of this processes is its ability to increase the efficacy of information transmission across synapses and thereby store memory contents. This process is called synaptic plasticity. Manahan-Vaughan and Strauch were the first to show that stimulation of the anterior piriform cortex triggers synaptic plasticity in the hippocampus.
Special role for olfaction
In a second step, the researchers examined to what extent the piriform cortex competes with the entorhinal cortex in driving hippocampal synaptic plasticity. This structure sends information about activity in all sensory modalities to the hippocampus. Activating the afferent pathway of this structure, called the perforant path, triggered completely different reaction patterns in the hippocampus, to those generated by the piriform cortex. "The study gives us a theoretical basis for understanding how olfaction plays such a special role in memory formation and retrieval," commented Denise Manahan-Vaughan.
The two scientists have been working together since 2010 to investigate how odours cause memory formation.
Memory Enhancement Breakthrough: Sending Safe Electrical Impulses To The Brain At The Right Time
For decades, scientists have been going through tons of medical studies for memory enhancement. And finally, a breakthrough. In a research published in the journal Current Biology, neuroscientists from the University of Pennsylvania have shown that it may be possible to improve memory by using tiny pulses of electricity at exactly the right time. Stimulating the brain when it is predicted to function poorly is effective in enhancing memory. On the other hand, stimulating the brain when it is functioning well impairs memory. The timing made all the difference.
The subjects of the research were a group of patients who have severe epilepsy. As part of their treatment, these individuals already had electrodes temporarily implanted in their brains, facilitating the study using electric stimulation of the brain. However, the earlier studies did not yield successful results. There were times that memory enhancement was achieved and times that memory was impaired.
The team continued studying more epilepsy patients for memory enhancement applications. According to the head of the research team, Michael Kahana, this time, they examined how the effects of stimulation differ during poor memory function versus effective memory function. The study involved patients being treated for epilepsy at the Hospital of the University of Pennsylvania, the Thomas Jefferson University Hospital, the Dartmouth-Hitchcock Medical Center, the Emory University Hospital, the University of Texas Southwestern, the Mayo Clinic, Columbia University, the National Institutes of Health Clinical Center and the University of Washington, as reported by the New York Times.
While receiving safe levels of electrical brain impulses, participants were asked to study and recall lists of common words. During this process, electrical activity from electrodes implanted in the patients' brains was recorded. Records showed that the identification of electrical patterns predicted whether the patient was going to remember something or not.
The team then did the experiment during their period of effective memory and during their period of poor memory. The result was a breakthrough. The scientists discovered that when electrical impulses arrive during periods of effective memory, memory worsens. But when the electrical impulse zaps at times of poor function, memory is considerably improved, as reported by Medical Press.
The researchers hope their findings of the memory enhancement breakthrough would be a major step in the goal of helping people with all kinds of brain injury or diseases. The research was funded by the Defense Advanced Research Projects Agency (DARPA) in an effort to help the troops returning from Iraq and Afghanistan with memory problems caused by traumatic brain injuries.
Plants cannot "think and remember," but there's nothing stupid about them: They're shockingly sophisticated
Plants can transmit information "from leaf to leaf in a very similar way to our own nervous systems," BBC News wrote. The article continues to assert that plants remember information and use "information encrypted in the light to immunize themselves against seasonal pathogens."
Plants cannot think or remember. These borrowed terms do not accurately describe how plants function. However, like most organisms, plants can sense the world around them, process information from their environment, and respond to this information by altering their growth and development. In fact, plants respond to changes in their environment in ways that many would find surprisingly sophisticated, although botanists have known of these abilities for centuries.
"A big mistake people make is speaking as if plants 'know' what they're doing," says Elizabeth Van Volkenburgh, a botanist at the University of Washington. "Biology teachers, researchers, students and lay people all make the same mistake. I'd much rather say a plant senses and responds, rather than the plant 'knows.' Using words like 'intelligence' or 'think' for plants is just wrong. Sometimes it's fun to do, it's a little provocative. But it's just wrong. It's easy to make the mistake of taking a word from another field and applying it to a plant."
The BBC News story is based on a study set for publication in The Plant Cell. Co-author Stanislaw Karpinski of the Warsaw University of Life Sciences in Poland recently presented his research at the annual meeting of the Society for Experimental Biology in Prague, Czech Republic.
The story maintains that, according to the study, stimulating one leaf cell with light creates a cascade of electrochemical events across the entire plant, communicated via specialized cells called bundle-sheath cells just as electrical impulses are propagated along the nerve cells in the nervous system of an animal. The researchers found that these reactions continued several hours later, even in the dark, which they interpreted to indicate a kind of memory.
This is like saying that because the surface of a pond continues to ripple once struck by a pebble, the water is "remembering" something. The analogy doesn't quite hold. But plants do produce electrical signals and the function of these signals in response to light is the real focus of the new study—the most recent contribution to a growing body of work about electrical signaling in plants.
Although plants don't have nerves, plants cells are capable of generating electrical impulses called action potentials, just as nerve cells in animals do. In fact, all biological cells are electrical.
Cells use membranes to keep their interiors separate from their exteriors. Some very tiny molecules can infiltrate the membranes, but most molecules must pass through pores or channels found within the membrane. One group of migratory molecules is the ion family: charged particles like sodium, potassium, chloride and calcium.
Whenever different concentrations of ions accumulate on opposite sides of a cell membrane, there exists the potential for an electrical current. Cells manage this electric potential using protein channels and pumps embedded in the cell membrane—gatekeepers that regulate the flow of charged particles across the cell membrane. The controlled flow of ions in and out of a cell constitutes electrical signaling in both plants and animals.
"In any cell you have a membrane," explains Alexander Volkov, a plant physiologist at Oakwood University in Alabama. "You have ions on both sides in different concentrations, which creates an electrical potential. It doesn't matter if it's an animal or plant cell—it's general chemistry."
Because certain types of plant cells have some features in common with nerve cells—they are arranged in tubular bundles, they harbor ion channels in their membranes—some botanists have suggested that plants propagate action potentials along connected networks of these cells, akin to signaling in an animal's nervous system. But most botanists agree that plants don't have networks of cells that have evolved specifically for rapid electrical signaling across long distances, as most animals do. Plants simply don't have true nervous systems.
So if plants aren't using electrical signals in nervous systems like animals, what do they do with the electrical impulses they produce? In most cases, plant biologists don't know. "We've known about electrical signaling in plants for as long as we've known about it in animals," says Van Volkenburgh. "But in most plants, what those signals are for is an open question." The notable exceptions to this mystery are plants that rely on electric signals for rapid movement, like the carnivorous Venus flytrap or Mimosa pudica—a plant whose leaves fold up when brushed to discourage herbivores (see movie below).
In recent years, some research has suggested that electrical signaling in plants modifies and regulates all kinds of biological processes in plant cells. Electrical signals, some botanists have argued, power more than the snapping traps of the exotic Venus flytrap—they are just as important for the grass growing on your lawn. Measuring electrical impulses in plants is easy, but linking them to specific plant functions is much more difficult and the plant biology community is nowhere near reaching a consensus about how most plants use those impulses.
Karpinski's new study attempts to link light-activated electrical activity to immune defenses in plants. In the new study, researchers infected the leaves of Arabidopsis thaliana (thale cress) with a bacterial pathogen either one hour before exposing the plant to a strong dose of blue, red or white light or one, eight or 24 hours after exposing the plant to light. Plants treated with light before infection developed resistance, but plants infected without any preceding illumination showed no resistance.
When exposed to strong light, Karpinski explains, plants absorb more energy than they can use for photosynthesis—but he doesn't think plants waste this excess energy. Karpinski says plants convert the energy to heat and electrochemical activity that can later trigger biological processes, like immune defenses. "It seems that plants can raise resistance against pathogens only using their light absorption system," Karpinski says. "We found that electrochemical signaling is regulating this process. Electrical signaling in plants is known from the time of Darwin—it is nothing new. But what was not described is that light can induce action potentials. We have found there is a different signaling for blue, white and red light. If plants can signal differently different wavelengths of light, then plants can see colors as well."
Karpinski thinks plants generate different electrical impulses when different wavelengths of light hit their leaves and that plants use these impulses to somehow regulate their immune defenses. He even speculates that plants can use this ability to battle seasonal pathogens. But exactly how this mechanism would work is unclear.
The role of electrical signaling in most plants remains largely mysterious and unexplained—and certainly does not warrant claims that plants can "think and remember." But there are plenty of well-documented examples of the sophisticated ways in which plants change their own growth in response to changes in their environment.
Just think about the fact that roots always grow in the direction of gravity and shoots always grow toward the light—even if you turn a plant on its side. Biologists have worked out that these processes, called gravitropism and phototropism respectively, rely on hormones that change the rate of cellular growth in plant tissues: If one side of a root or shoot is growing faster than another, it&rsquos going to bend. Climbing plants, like vines and creepers, use similar mechanisms to respond to touch, clinging and curling around the first pole, wall, or branch they contact.
Plants also process information from their environment and change their growth based on that information. "Some plants flower as the days are getting shorter and others as the days are getting longer. They 'know' that the days are getting longer or shorter by having tabulated reactions to each day and night length," says Van Volkenburgh. "The way this works is based on the circadian rhythm of plants. People don't realize plants have a circadian rhythm just like animals do. Plants have all kinds of movement based on their circadian rhythms."
Young sunflowers and other young plants' flowering tops and leaves can trace the sun's arc from East to West—a phenomenon called heliotropism that ensures maximum light exposure during a crucial period of growth. Then there are more startling examples of plants changing in response to their environment. Consider the Telegraph plant: a peculiar Asian shrub with tiny satellite leaves that constantly swivel to monitor the light in its environment. The satellite leaves pivot so dependably and swiftly that you can actually observe them moving in real time (see movie below). Their perpetual dance tracks the movement of light over the course of the day, adjusting the position of the primary leaves to absorb as much light as possible.
With such surprising examples of plants' abilities to process information and adapt to their environments, there's no need to try and endow plants with intelligence, thought, memory or other cognitive abilities they do not truly possess and do not need. They're plenty smart already.
Image of leaf courtesy of Wikimedia Commons
The views expressed are those of the author(s) and are not necessarily those of Scientific American.
ABOUT THE AUTHOR(S)
Ferris Jabr is a contributing writer for Scientific American. He has also written for the New York Times Magazine, the New Yorker and Outside.
In this chapter, you learned about the human nervous system. Specifically, you learned that:
- The nervous system is the organ system that coordinates all of the body&rsquos voluntary and involuntary actions by transmitting signals to and from different parts of the body. It has two major divisions, the central nervous system (CNS) and the peripheral nervous system (PNS).
- The CNS includes the brain and spinal cord.
- The PNS consists mainly of nerves that connect the CNS with the rest of the body. It has two major divisions: the somatic nervous system and the autonomic nervous system. The somatic system controls activities that are under voluntary control. The autonomic system controls activities that are involuntary.
- The autonomic nervous system is further divided into the sympathetic division, which controls the fight-or-flight response the parasympathetic division, which controls most routine involuntary responses and the enteric division, which provides local control for digestive processes.
- Signals sent by the nervous system are electrical signals called nerve impulses. They are transmitted by special, electrically excitable cells called neurons, which are one of two major types of cells in the nervous system.
- Glial cells are the other major type of nervous system cells. There are many types of glial cells, and they have many specific functions. In general, glial cells function to support, protect, and nourish neurons.
- The main parts of a neuron include the cell body, dendrites, and axon. The cell body contains the nucleus. Dendrites receive nerve impulses from other cells, and the axon transmits nerve impulses to other cells at axon terminals. A synapse is a complex membrane junction at the end of an axon terminal that transmits signals to another cell.
- Axons are often wrapped in an electrically-insulating myelin sheath, which is produced by glial cells. Electrical impulses called action potentials occur at gaps in the myelin sheath, called nodes of Ranvier, which speeds the conduction of nerve impulses down the axon.
- Neurogenesis, or the formation of new neurons by cell division, may occur in a mature human brain but only to a limited extent.
- The nervous tissue in the brain and spinal cord consists of gray matter, which contains mainly the cell bodies of neurons and white matter, which contains mainly myelinated axons of neurons. Nerves of the peripheral nervous system consist of long bundles of myelinated axons that extend throughout the body.
- There are hundreds of types of neurons in the human nervous system, but many can be classified on the basis of the direction in which they carry nerve impulses. Sensory neurons carry nerve impulses away from the body and toward the central nervous system, motor neurons carry them away from the central nervous system and toward the body, and interneurons often carry them between sensory and motor neurons.
- A nerve impulse is an electrical phenomenon that occurs because of a difference in electrical charge across the plasma membrane of a neuron.
- The sodium-potassium pump maintains an electrical gradient across the plasma membrane of a neuron when it is not actively transmitting a nerve impulse. This gradient is called the resting potential of the neuron.
- An action potential is a sudden reversal of the electrical gradient across the plasma membrane of a resting neuron. It begins when the neuron receives a chemical signal from another cell or some other type of stimulus. The action potential travels rapidly down the neuron&rsquos axon as an electric current.
- A nerve impulse is transmitted to another cell at either an electrical or a chemical synapse. At a chemical synapse, neurotransmitter chemicals are released from the presynaptic cell into the synaptic cleft between cells. The chemicals travel across the cleft to the postsynaptic cell and bind to receptors embedded in its membrane.
- There are many different types of neurotransmitters. Their effects on the postsynaptic cell generally depend on the type of receptor they bind to. The effects may be excitatory, inhibitory, or modulatory in more complex ways. Both physical and mental disorders may occur if there are problems with neurotransmitters or their receptors.
- The CNS includes the brain and spinal cord. It is physically protected by bones, meninges, and cerebrospinal fluid. It is chemically protected by the blood-brain barrier.
- The brain is the control center of the nervous system and of the entire organism. The brain uses a relatively large proportion of the body&rsquos energy, primarily in the form of glucose.
- The brain is divided into three major parts, each with different functions: brain stem, cerebellum, and cerebrum. The cerebrum is further divided into left and right hemispheres. Each hemisphere has four lobes: frontal, parietal, temporal, and occipital. Each lobe is associated with specific senses or other functions.
- The cerebrum has a thin outer layer called the cerebral cortex. Its many folds give it a large surface area. This is where most information processing takes place.
- Inner structures of the brain include the hypothalamus, which controls the endocrine system via the pituitary gland and the thalamus, which has several involuntary functions.
- The spinal cord is a tubular bundle of nervous tissues that extends from the head down the middle of the back to the pelvis. It functions mainly to connect the brain with the PNS. It also controls certain rapid responses called reflexes without input from the brain.
- A spinal cord injury may lead to paralysis (loss of sensation and movement) of the body below the level of the injury because nerve impulses can no longer travel up and down the spinal cord beyond that point.
- The PNS consists of all the nervous tissue that lies outside of the CNS. Its main function is to connect the CNS to the rest of the organism.
- The tissues that make up the PNS are nerves and ganglia. Ganglia act as relay points for messages that are transmitted through nerves. Nerves are classified as sensory, motor, or a mix of the two.
- The PNS is not as well protected physically or chemically as the CNS, so it is more prone to injury and disease. PNS problems include injury from diabetes, shingles, and heavy metal poisoning. Two disorders of the PNS are Guillain-Barre syndrome and Charcot-Marie-Tooth disease.
- The human body has two major types of senses, special senses, and general senses. Special senses have specialized sense organs and include vision (eyes), hearing (ears), balance (ears), taste (tongue), and smell (nasal passages). General senses are all associated with touch and lack special sense organs. Touch receptors are found throughout the body but particularly in the skin.
- All senses depend on sensory receptor cells to detect sensory stimuli and transform them into nerve impulses. Types of sensory receptors include mechanoreceptors (mechanical forces), thermoreceptors (temperature), nociceptors (pain), photoreceptors (light), and chemoreceptors (chemicals).
- Touch includes the ability to sense pressure, vibration, temperature, pain, and other tactile stimuli. The skin includes several different types of touch receptor cells.
- Vision is the ability to sense light and see. The eye is the special sensory organ that collects and focuses light, forms images, and changes them to nerve impulses. Optic nerves send information from the eyes to the brain, which processes the visual information and &ldquotells&rdquo us what we are seeing.
- Common vision problems include myopia (nearsightedness), hyperopia (farsightedness), and presbyopia (age-related decline in close vision).
- Hearing is the ability to sense sound waves, and the ear is the organ that senses sound. It changes sound waves to vibrations that trigger nerve impulses, which travel to the brain through the auditory nerve. The brain processes the information and &ldquotells&rdquo us what we are hearing.
- The ear is also the organ that is responsible for the sense of balance, which is the ability to sense and maintain an appropriate body position. The ears send impulses on head position to the brain, which sends messages to skeletal muscle via the peripheral nervous system. The muscles respond by contracting to maintain balance.
- Taste and smell are both abilities to sense chemicals. Taste receptors in taste buds on the tongue sense chemicals in food and olfactory receptors in the nasal passages sense chemicals in the air. The sense of smell contributes significantly to the sense of taste.
- Psychoactive drugs are substances that change the function of the brain and result in alterations of mood, thinking, perception, and/or behavior. They include prescription medications such as opioid painkillers, legal substances such as nicotine and alcohol, and illegal drugs such as LSD and heroin.
- Psychoactive drugs are divided into different classes according to their pharmacological effects. They include stimulants, depressants, anxiolytics, euphoriants, hallucinogens, and empathogens. Many psychoactive drugs have multiple effects so they may be placed in more than one class.
- Psychoactive drugs generally produce their effects by affecting brain chemistry. Generally, they act either as agonists, which enhance the activity of particular neurotransmitters or as antagonists, which decrease the activity of particular neurotransmitters.
- Psychoactive drugs are used for various purposes, including medical, ritual, and recreational purposes.
- Misuse of psychoactive drugs may lead to addiction, which is the compulsive use of a drug despite negative consequences. Sustained use of an addictive drug may produce physical or psychological dependence on the drug. Rehabilitation typically involves psychotherapy and sometimes the temporary use of other psychoactive drugs.
In addition to the nervous system, there is another system of the body that is important for coordinating and regulating many different functions &ndash the endocrine system. You will learn about the endocrine system in the next chapter.
What an Anti-Memory Is and How It Frees Your Mind
Wonder how your brain makes space for new memories? Scientists at Oxford just discovered how.
Neuroscientists at Oxford just discovered how your brain moves memories into long-term storage. It’s called an anti-memory, and it’s more helpful than it sounds.
Memories, at their most basic, are electrical impulses. But what happens if those impulses are always firing? Would they overload your brain the same way that running too many programs on your computer would fry its RAM? The answer is yes. Scientists think that these overly excited neurons could be the culprits behind conditions like epilepsy, schizophrenia, and autism . The balancing agent that keeps that from happening are anti-memories.
Think of them as defragging a memory’s RAM. Anti-memories are neurons that lower the electrical activity generated by memory creation. Anti-memories work together with memories to keep the brain from getting overloaded. They don’t affect memories they just silence the process running them so your brain can do other things.
When you form a memory, your brain assembles it from different parts of your brain, rebuilding it each time from scratch. There are three steps to building a memory -- encoding it (intentionally committing it to memory), consolidating it (different parts of the brain acting gluing the memory together) and retrieving it (recalling the memory). Every time you retrieve a memory, you increase your brain’s ability to recall it by strengthening the neural pathway to that memory. That makes the memory stronger and easier to recall in the long run. Here’s a quick primer:
Credit: Head Squeeze, Brit Lab/YouTube
Anti-memories work in the same way, just in reverse. Scientists had long theorized their existence from models and studies on mice . Neurologists at the University of Oxford were finally able to observe them in humans with this experiment, whose findings were published in the journal Neuron . Lead author Helen Barron explains the process in a press release :
To measure these links, or associative memories, we use a technique called repetition suppression where repeated exposure to a stimulus – the shapes in this case – causes decreasing activity in the area of the brain that represents shapes. By looking at these suppression effects across different stimuli we can use this approach to identify where memories are stored.
The memory paths identified in the study. Credit: Neuron
The researchers were able to do this by observing participants’ brain activity as they memorized the shapes using functional magnetic resonance imaging (fMRI). Over time, the anti-memory neurons kicked in and blocked the memories of the shapes. “Over 24 hours, the shape associations in the brain became silent,” said Barron. Most interestingly, they didn’t look like additional memories they looked like an absence of brain activity. They're not - they're just active on the same neural path. Think of it as someone retracing their steps, like this:
That could have been because the brain was rebalanced or it could simply be that the associations were forgotten. The following day, some of the volunteers undertook additional tests to confirm that the silencing was a consequence of rebalancing. If the memories were present but silenced by inhibitory replicas, we thought that it should be possible to re-express the memories by suppressing inhibitory activity.
In order to re-express the memories, researchers used transcranial direct current stimulation (tDCS) to apply a low current of electricity to the volunteers’ brains. By doing this, the researchers reduced the activity of the anti-memory neurons -- and the memories of the shape associations came back.
"This result is consistent with a balancing mechanism,” Barron says. “The increase in excitation seen in learning and memory formation, when excitatory connections are strengthened, appears to be balanced out by a strengthening of inhibitory connections."
While the sample size for this study was small, the research team has big hopes for their findings. "The paradigm has the potential to be translated directly into patient populations, including those suffering from schizophrenia and autism," said Barron. "We hope that this research can now be taken forward in collaboration with psychiatrists and patient populations so that we can develop and apply this new understanding to the diagnosis and treatment of mental disorders."
Where are you standing in your memory?
In a new study from the University of Alberta, researchers looked at which areas of the brain are activated when we remember.
When we remember an experience in the usual way, we do it from the first person viewpoint as though we are reliving it. We see our memory through our own eyes and re-experience it.
But when we remember from the third person viewpoint, as though we are looking at ourselves from the outside in, we find a new perspective. And so does our brain. While recalling memories as an observer, the brain shows greater interaction between the anterior hippocampus and the posterior medial network. That means there is more interaction between the areas of the brain that support memory.
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Perhaps even more interesting, the third person perspective leads the brain to activate two distinct memory networks when retrieving the memory. Looking at it through our own eyes vs. looking at it as an observer literally leads to different brain activity. And that has interesting implications.
"Adopting an observer-like perspective involves viewing the past in a novel way, which requires greater interaction among brain regions that support our ability to recall the details of a memory and to recreate mental images in our mind's eye,” said said Peggy St Jacques, assistant professor of psychology and co-author on the paper in a press release. Greater interaction between brain areas typically means the brain is not just remembering, but processing those memories.
Electric pulses to the brain can improve memory as much as 15 per cent, finds study
Sending electric pulses to the brain can improve memory by as much as 15 per cent, scientists have found.
The team used a technique which monitors brain activity to identify when it’s not effectively storing new information, and send a helpful zap which helps commit it to memory.
It is the first time that consistent memory improvements have been demonstrated in a human trial, according to the new study's authors.
It represents and early step towards technologies that may one day improve memory function in patients with Alzheimer’s disease or traumatic brain injury.
“We are now able to monitor when the brain seems to be going off course and to use stimulation to correct the trajectory,” said Michael Sperling, a clinical study investigator at Thomas Jefferson University Hospital whose patients participated in the trial.
The research was funded by the US Department of Defense as part of its Restoring Active Memory (RAM) project which it hopes will develop implantable technologies to support veterans.
The team, from the University of Pennsylvania, used an AI system which can monitor brain activity and learn to trigger the electrodes when the subject’s memory is predicted to fail.
“Memory failures are frustrating and often the result of ineffective encoding," they wrote in the study, published in the journal Nature Communications. “One approach to improving memory outcomes is through direct modulation of brain activity with electrical stimulation.”
Deep brain stimulation has been used in treating conditions like Parkinson’s disease and epilepsy for decades, but it is now being looked at for conditions like Alzheimer’s disease and memory loss.
For the trial, the team recruited 25 epilepsy patients who had already undergone surgery to have electrodes in their brain as part of routine treatment where the disease is not controlled with medication.
They were asked to take a number of word recall tests and their brain activity was monitored in real time, with a computer program tracking how effectively each word had been remembered.
As the program learned to recognise ineffective learning, it would trigger a small electric pulse at these points.
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“Lateral temporal cortex stimulation increased the relative probability of item recall by 15 per cent,” the authors wrote.
Previous work by the group has had problems when using a less targeted “open-loop” system which sees parts of the brain linked to memory given electronic impulses at regular repeating intervals.
“We knew from earlier work that stimulating the brain during periods of good function was likely to make memory worse,” said Professor Michael Kahana, a co-author of this study and principal investigator on the RAM project.
“By developing patient-specific, personalized, machine-learning models we could programme our stimulator to deliver pulses only when memory was predicted to fail, giving this technology the best chance of restoring memory function.”
Independent academics said the findings were “innovative and exciting”.
However they warned that, because this is the first trial to show such an effect it would need to be replicated in more patients, and with diseases like dementia, before conclusions of its effectiveness can be drawn.
“This is a well-designed study that provides convincing results about the potential to improve memory using invasive brain stimulation and a closed-loop approach,” said Professor Roi Cohen Kadosh, professor of cognitive neuroscience, University of Oxford, who was not associated with the study.
“The results, while exciting, do not at this stage have therapeutic implications and would need to be replicated in clinical populations such as Alzheimer’s disease. Whether this could be found using non-invasive, rather than invasive, brain stimulation techniques is an open question that deserves further research.”
Dr David Reynolds, chief scientific officer, at Alzheimer’s Research UK, said the electrodes here stimulate a different part of the brain than would be targeted in Alzheimer’s patinets.
“Although it’s promising to see tests of this innovative device, which can detect and be trained to recognise areas of brain that may benefit from further stimulation, we cannot yet say whether it will benefit people living with dementia.”
Impaired Recall of Positional Memory following Chemogenetic Disruption of Place Field Stability
The neural network of the temporal lobe is thought to provide a cognitive map of our surroundings. Functional analysis of this network has been hampered by coarse tools that often result in collateral damage to other circuits. We developed a chemogenetic system to temporally control electrical input into the hippocampus. When entorhinal input to the perforant path was acutely silenced, hippocampal firing patterns became destabilized and underwent extensive remapping. We also found that spatial memory acquired prior to neural silencing was impaired by loss of input through the perforant path. Together, our experiments show that manipulation of entorhinal activity destabilizes spatial coding and disrupts spatial memory. Moreover, we introduce a chemogenetic model for non-invasive neuronal silencing that offers multiple advantages over existing strategies in this setting.
Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.
Figure 1. The GlyCl Transgene Vector and…
Figure 1. The GlyCl Transgene Vector and Its Expression in the Nop-tTA Model
Figure 2. Neuronal Silencing with Ivermectin in…
Figure 2. Neuronal Silencing with Ivermectin in Acute Brain Slice Preparations
Figure 3. In Vivo Pharmacokinetics and Pharmacodynamics…
Figure 3. In Vivo Pharmacokinetics and Pharmacodynamics of Ivermectin Silencing
(A and B) Liquid chromatography-tandem…
Figure 4. IVM Silencing Causes Place Field…
Figure 4. IVM Silencing Causes Place Field Instability in Nop-GlyCl Mice
(A) Between-session stability was…
Figure 5. Decreased Specificity of Spatial Tuning…
Figure 5. Decreased Specificity of Spatial Tuning following Entorhinal Silencing in Nop-GlyCl Mice
Figure 6. Neuronal Silencing in Nop-GlyCl Mice…
Figure 6. Neuronal Silencing in Nop-GlyCl Mice Induces Global Remapping of CA1 Place Fields
Figure 7. Neuronal Silencing in Nop-GlyCl Mice…
Figure 7. Neuronal Silencing in Nop-GlyCl Mice Impairs Spatial Recall in the Morris Water Maze
How Amnesia Works
Imagine for a moment what life would be like with a perfect memory. If you could remember each detail of everything taken in by your five senses, the first hour of the day would be mentally overwhelming -- truly too much information. That is why the brain sorts all of that data into your short-term memory or long-term memory or discards it.
Short-term memory allows us to retain information we need in the moment and then get rid of it. It's the mental equivalent of a takeout box. You use it to temporarily store small amounts of information and toss it afterward. Likewise, the short-term memory holds up to seven pieces of information for about 20 to 30 seconds [source: Canadian Institute of Neurosciences, Mental Health and Addiction]. Long-term memory is more like your internal freezer. It can hold information for years, or even a lifetime, but without some use, stuff in there can get "freezer burned."
We make and store memories by forging new neural pathways to the brain from things we take in through our five senses. The stimuli that our nerve cells detect, such as hearing a gunshot or tasting a raspberry, are called sensory memories. That sensory information flows along the nerve cells as an electrical impulse. As that impulse reaches the end of a nerve, it activates neurotransmitters, or chemical messengers. Those neurotransmitters send the message across the spaces between nerve cells called synapses and move it along to the neurons, or brain cells. If we need to immediately use that sensory information, it moves to the short-term memory, for example, when we hear a phone number and have to remember it to dial.
To turn short-term memories into long-term ones, our brains must encode, or define, the information. Remember that raspberry? Encoding it would likely include cataloging the fruit's size, tartness and color. From there, the brain cells would consolidate the information for storage by linking it to related memories. During this process, that neural pathway strengthens because of the brain's plasticity. Plasticity allows the brain to change shape to take in new information and, thus, new pathways.
Long-term memory retrieval requires revisiting the nerve pathways the brain formed. The strength of those pathways determines how quickly you recall the memory. To reinforce that initial memory, it must move multiple times across the nerve cells, retracing its steps.
Memory formation largely occurs in the brain's limbic system, which regulates learning, memory and emotions. The cortex is the temporary storage place of short-term memories and the area where the brain puts the new stimuli into context. The hippocampus then interprets the new information, associates it with previous memories and determines whether to encode it as a long-term memory. Next, the hippocampus sends the long-term memories to different areas of the cortex, depending on the type of memory. For instance, the amygdala houses intensely emotional memories. The memories are then stored in the synapses where they can be reactivated later.
Next, we'll see what happens when those neural pathways that make our memories are cut off by a roadblock called amnesia.
Episodic/Explicit — memories based on specific facts and information. When studying for a test, you exercise your explicit memory.
Procedural/Implicit — sensory and motor memories, such as riding a bike or playing a guitar
Semantic — organized and categorized memories. For instance, if asked your favorite band, your semantic memory filters through music-related information to come up with a band name.
Take a second to think about what you’re afraid of. It might be spiders. Or the threat of a car crash. It may be as basic as not having enough money to pay your rent next month. For many of us, these fears are tied to memories of past experiences.
When we form episodic memories of things that happened to us, three areas of the brain are engaged: the hippocampus, the neocortex and the amygdala. The hippocampus takes the information from our memories and physically encodes it into the connections between neurons. Later, this data is sometimes transferred to the neocortex — the thin tissue that forms the brain’s outer layer — for long-term storage. But it is the amygdala, an almond-shaped mass of brain matter, that injects our memories with emotions like fear.
“If an experience has a strong emotional component, the amygdala will squirt that into the newly forming memory,” says Burnett. “If someone has an active amygdala, they learn to be scared of things.”
In recent years, scientists have learned a lot about the hardware in our brains that modulates our responses to fearful memories. At the Queensland Brain Institute in Australia, researchers are recording the electrical activity firing between these three brain regions in mice as they are conditioned to fear a particular sensation or noise.
“You take a neutral stimulus, like a tone or a light, and with that you present the animal with an aversive stimulus, like a foot shock or a loud noise,” says neuroscientist Pankah Sah, the institute’s director. “And the animal pretty quickly learns that this innocuous stimulus is going to predict this aversive one. Then it forms the memory of it.
“If you do that in rats three or four times today, and come back a year later and present the same tone, that animal remembers that the tone was scary and responds appropriately,” he adds. “You can do the same thing in people.”
That conditioning can be exploited for good, too. If the mouse repeatedly hears that same tone again, but without the shock, then the noise will stop causing the animal to freeze in fear. Eventually, through a process called extinction learning, the pain of the memory fades away. This process is key to behavioral therapies for patients with conditions like PTSD . But despite the effectiveness of these techniques, extinction training doesn’t erase traumatic memories — it just saps some of their strength. If something reminds someone of the original traumatic memory in a new context, even after extinction, it can solidify again, re-forming the link between the trigger and the response. “People who are injecting heroin can learn to not do it,” says Sah. “But when the context changes, or something happens in the environment and it’s not a place where it’s safe anymore, all those memories come back.”
Sah thinks that a sharper understanding of why some traumatic memories return after therapy may lead to better treatments for disorders such as PTSD and addiction. In a 2018 Nature Neuroscience study, Sah and his colleagues used optogenetics in rats to identify the circuitry in the brain that controls the return of traumatic memories . By understanding those mechanisms, says Sah, it might be possible to develop new drugs to prevent relapses. “What we’re looking for is a more specific [chemical] compound,” he continues. “That’s how you go about really treating these disorders: understanding the circuits that underpin [them] and the receptors that are involved.”
And thanks to a tidal wave of new tech, Sah says these advances might someday help scientists treat memory disorders the same way that we use drugs to control heart disease. “The whole study of the brain is really undergoing a revolution right now,” he adds. “It’s really a great time to be in neuroscience.”