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Does one memory cell take part in different memories? For example, both in the visual memory of a bird and a monkey?
According to engram theory: Yes.
However, you need more than one cell to encode a memory engram. The idea is that the combination of cells encodes the memory, not the cells themselves.
I am most familiar with the hippocampus, in which cells participating in the encoding of "concepts" like Jennifer Aniston, Bill Clinton or the Sydney Opera House have been found in humans Quiroga et al. (2008)
Scientists reveal more about how memories are formed
Researchers at the University of Leicester working alongside colleagues in the US, have found that nerve cells in a brain region called the medial temporal lobe play a key role in the rapid formation of new memories about personal experiences and life events.
Thoughts and recollections are the result of complex networks of nerve cells activating or 'firing' in the brain. There are different kinds of memory that involve different systems of nerve cells in various parts of the brain. Episodic memory is memory for events experienced through life and allows people to recall information like where they first met a friend. It is usually this type of memory that is first affected by Alzheimer's disease, leaving people unable to recall events from their recent past even when they can remember abstract facts and other information.
This study involved fourteen people with severe epilepsy, who were fitted with electrodes to monitor 600 individual nerve cells in the medial temporal lobe. While the electrodes were implanted to determine what surgery might help them, they also volunteered to take part in a simple experiment.
To begin with, the participants viewed separate images of familiar people, such as family members or celebrities, and famous landmarks, such as the Eiffel Tower and the Pyramids of Giza. Using the electrodes the researchers could see different nerve cells respond to different images. A nerve cell that fired when a participant saw a picture of a celebrity like Clint Eastwood wouldn't fire when the person saw a landmark like the Pyramids.
Next the researchers showed the volunteers a series of pictures which included both a familiar person and a place, digitally combined to create the impression of a photograph of the person taken at the landmark. After showing the combined picture to the participants only a very few times, they learned to associate the person and place, such as Clint Eastwood at the Pyramids. This kind of association is part of episodic memory. Once the participant learned the link, nerve cells which had previously responded only to Clint Eastwood, would fire when the participant saw a picture of just the Pyramids and vice versa. This finding reveals more about the mechanism used by the brain to create new memories, knowledge which could also provide insights into how this process can break down in disease.
Dr Laura Phipps of Alzheimer's Research UK said:
"Associating different aspects of a life experience is crucial for the formation of new memories and this research sheds new light on the biology underlying this process. While this study did not investigate memory in people with dementia, problems with the formation of new memories are characteristic of diseases like Alzheimer's. These symptoms can be extremely distressing for the person experiencing them as well as for those around them. Understanding more about the way our brains form and retrieve memories is an important step towards understanding how diseases like Alzheimer's affect the brain and what might be done to help those living with these conditions.
"The human brain is the most complex structure known to man and we need to better understand the way it works so that we can develop strategies to intervene when things go wrong. With 850,000 people affected by dementia in the UK, and that number on the rise, we need to make sure basic research into the way the brain works continues so that this work can inform the hunt for new treatments."
Active, inactive cells in the brain's memory system
For the first time, Tübingen neuroscientists were able to differentiate between active and inactive cells in the brain morphologically, i.e. based on the cells' structure. Investigating granule cells in the rat's brain, they found a much larger proportion of inactive than active cells.
Many things we think we know about the world have their origin in popular culture, not science. The most well-known false 'fact' about the brain is the misconception that we only use ten percent of the brain's overall capacity. This so-called 'ten percent myth', while accepted as such by neuroscientists, still regularly figures in advertisement, but also in books and short stories as well as films. As with any myth, however, there is a kernel of truth at the core of the matter: many neurons remain dormant for most if not all of our life, even while their direct neighbours show regular activity.
A team of neuroscientists led by Dr. Andrea Burgalossi of the Werner Reichardt Centre for Integrative Neuroscience (CIN) at the University of Tübingen have now taken an important step towards understanding why some neurons are active and others are not: they can tell them apart morphologically. To be able to do so, the investigators employed so-called juxtacellular recordings in freely-moving rats. With this technique, electrodes are inserted right next to individual, functioning neurons in live organisms. This allows recording action potentials from these neurons while they work, and while simultaneously identifying the cells that the recordings are taken from for later analysis.
During this analysis, morphological traits of the analysed cells are identified, most importantly their dendritic arbors, i.e. the filament structures which receive input signals from other neurons. The cells under investigation were granule cells (GCs) in the rat's dentate gyrus (DG). Dentate GCs have been shown to be intimately connected to individual memories of places and individuals, and thus playing a central role in memory tasks.
The researchers recorded from 190 GCs, only 27 of which they found to be active (ca. 14 percent). While this seems to give credibility to the 'ten percent myth', the team actually expected this outcome, as the DG is a brain structure where in any given task, only a very small percentage of neurons take part, while their neighbours remain dormant, waiting for their 'cue', as it were. Memory functions in the brain work according to a principle that neuroscientists call 'sparse coding', i.e. a comparatively small number of neurons encode complex information -- possibly to make overlap between different memories more unlikely.
Using a smaller subsample, the scientists looked for correlations between active and passive functionality and the respective cells' morphology. Their results show that active GCs have much more complex dendritic arbors. They not only transfer and receive information from many more neurons than the inactive ones, they also have better cellular 'infrastructure' to do so. Despite their as of yet limited sampling, the scientists are positive that they can now tell apart active and inactive GCs, mostly by merely looking at them. "Explaining the causes of activity in some and inactivity in other neurons may still take a long time," cautions Burgalossi, leader of the research group. "But finding a direct link between function and morphology is an important step forward. It will be even more challenging to find evidence of causality. But we are on the right track."
How acquiring The Knowledge changes the brains of London cab drivers
London is not a good place for fans of right angles. People who like the methodical grid system of Manhattan will whimper and cry at the baffling knot of streets of England’s capital. In this bewildering network, it’s entirely possible to take two right turns and end up in the same place. Or in Narnia. Even with a map, some people manage to get lost. And yet, there are thousands of Londoners who have committed the city’s entire layout to memory – cab drivers.
Piloting London’s distinctive black cabs (taxis to everyone else) is no easy feat. To earn the privilege, drivers have to pass an intense intellectual ordeal, known charmingly as The Knowledge. Ever since 1865, they’ve had to memorise the location of every street within six miles of Charing Cross – all 25,000 of the capital’s arteries, veins and capillaries. They also need to know the locations of 20,000 landmarks – museums, police stations, theatres, clubs, and more – and 320 routes that connect everything up.
It can take two to four years to learn everything. To prove their skills, prospective drivers make “appearances” at the licencing office, where they have to recite the best route between any two points. The only map they can use is the one in their head. They even have to narrate the details of their journey, complete with passed landmarks, road names, junctions, turns and maybe even traffic lights. Only after successfully doing this, several times over, can they earn a cab driver’s licence.
Given how hard it is, it shouldn’t be surprising that The Knowledge changes the brains of those who acquire it. And for the last 11 years, Eleanor Maguire from University College London has been studying those changes.
In 2000, Maguire showed that one particular part of the brain – the hippocampus – is much larger in London cab drivers than in other people. This seahorse-shaped area lies in the core of the brain, and animal studies had linked it to memory and spatial awareness. Species that store a lot of food tend to have a bigger hippocampus than those without the need to remember any burial sites.
Maguire showed that the same applies to humans. Not only did cab drivers have an unusually large hippocampus, but the size of the area matched the length of their driving careers. Since then, taxi drivers have featured in many of Maguire’s experiments. “They know that they’re special,” she says.”What they’ve achieved when they’re qualified is extremely impressive, so they’re very willing to come and be tested.”
She showed that a driver’s hippocampus is most active when they first plan a route. She found that the hippocampus shrinks back to a normal size once drivers retire. And she found that acquiring The Knowledge comes at a cost – taxi drivers find it more difficult to integrate new routes into their existing maps, and other aspects of their memory seemed to suffer.
An enlarged hippocampus is a rare feature. You don’t see it in doctors who gain vast amounts of knowledge over many years. You don’t see it in memory champions who have trained themselves to remember seemingly impossible lists. You don’t see it in London’s bus drivers who have similar driving skills but work along fixed routes. Among all of these groups, only the London cabbies, with their superb spatial memories, have swollen hippocampi.
These studies strongly suggested that their intensive training was the reason for the changes in the taxi drivers’ brains. They helped to change the decades-old perception of the adult brain as a static organ. Instead, Maguire likens the brain to a muscle – exercise it and it gets stronger. “But of course,” she says, “the real test is to take people before they start training and test them afterwards, to see if there are changes in the hippocampus in the same individual. That would give the best evidence.”
Maguire, and her colleague Katherine Woollett, have done exactly that. They scanned their brains of 79 wannabe drivers who had just started their training. Three to four years later, they did the same thing. By this point, 39 of the trainees – just under half – had earned their licence. The rest had flunked out. The Knowledge is not easily won.
At the start of the study, the trainees had the same memory skills as each other, and 31 men with no aspirations of being cabbies. Everyone’s hippocampus was on a similarly level playing field. The second time round, things had changed. Woollett and Maguire found that the hippocampi of the qualified cabbies had grown in size, especially the back part. They were now significantly larger than those of either the failed trainees or the men who didn’t take part. The cabbies also outperformed their peers on spatial memory tasks.
This is the strongest evidence yet that the training that London cabbies undergo is directly responsible for the changes in their brain. The alternative – that someone with a large hippocampus is more likely to drive a taxi – just doesn’t hold.
Still, there are some unanswered questions. For a start, how exactly does studying for The Knowledge increase the rise of the hippocampus? This small area is one of only two parts of the brain that makes new neurons throughout our adult lives. These extra cells could account for the increased size of a cabbie’s hippocampus. Alternatively, the existing neurons could simply form better connections with one another. Maguire’s next challenge is to tease apart these possibilities.
Another question: why did half of the trainees fail to qualify? Most of them said that they couldn’t afford the time or money, while others cited family obligations. Those could all be valid reasons, but equally, they could be smokescreens that cover a deeper inability. Maguire wonders if genetic differences could give some people a natural edge and others a natural weakness, especially since some genes do affect the size of the hippocampus.
For the moment, Maguire thinks that her work on cab drivers has implications for everyone. “We’re in a situation where people are living longer and often have to retrain or re-educate themselves at various phases in their lives,” she says. “It’s important for people to know that their brains can support that. It’s not the case that your brain structure is fixed.”
She also wonders if her work could one day help people with memory problems, a group that she identifies with. “I’m grossly impaired. I can’t step outside my office without guidance. I keep on having to be talked into places by phone.” She laughs. “It’s very ironic. I’m very motivated to learn how the brain helps you navigate!”
Reference: Woollett & Maguire. 2011. Acquiring ‘‘the Knowledge’’ of London’s Layout Drives Structural Brain Changes. Current Biology http://dx.doi.org/10.1016/j.cub.2011.11.018
For more on the Knowledge and Maguire’s work, see this excellent piece by visiting American, Sally Adee.
Regulatory T Cells
Regulatory T cells are a subset of T cells which modulate the immune system and keep immune reactions in check.
Describe the function and types of regulatory T cells
- Regulatory T cells (Tregs) are critical to the maintenance of immune cell homeostasis as evidenced by the consequences of genetic or physical ablation of the Treg population.
- Tregs are classified into natural or induced Tregs natural Tregs are CD4+CD25+ T-cells which develop, and emigrate from the thymus to perform their key role in immune homeostasis.
- Adaptive Tregs are non-regulatory CD4+ T-cells which acquire CD25 (IL-2R alpha) expression outside of the thymus and are typically induced by inflammation and disease processes, such as autoimmunity and cancer.
- autoimmunity: The condition where one’s immune system attacks one’s own tissues, i.e., an autoimmune disorder.
Regulatory T cells are a component of the immune system that suppress immune responses of other cells. This is an important “self-check” built into the immune system to prevent excessive reactions and chronic inflammation. Regulatory T cells come in many forms, with the most well-understood being those that express CD4, CD25, and Foxp3. These cells are also called CD4 + CD25 + regulatory T cells, or Tregs. These cells are involved in shutting down immune responses after they have successfully eliminated invading organisms, and also in preventing autoimmunity.
CD25 is a component of the IL2 receptor: Interleukin 2 receptor is composed of three subunits (alpha, beta, and gamma). CD25 constitutes the alpha chain of the IL2 receptor.
CD4 + Foxp3 + regulatory T cells have been called “naturally-occurring” regulatory T cells, to distinguish them from “suppressor” T cell populations that are generated in vitro. Additional suppressor T cell populations include Tr1, Th3, CD8 + CD28 – , and Qa-1 restricted T cells. The contribution of these populations to self- tolerance and immune homeostasis is less well defined. FOXP3 can be used as a good marker for CD4+CD25+ T cells as well as recent studies showing evidence for FOXP3 in CD4+CD25- T cells.
An additional regulatory T cell subset, induced regulatory T cells, are also needed for tolerance and suppression. Induced Regulatory T (iTreg) cells (CD4 + CD25 + Foxp3 + ) are suppressive cells involved in tolerance. iTreg cells have been shown to suppress T cell proliferation and experimental autoimmune diseases. iTreg cells develop from mature CD4 + conventional T cells outside of the thymus: a defining distinction between natural regulatory T (nTreg) cells and iTreg cells. Though iTreg and nTreg cells share a similar function iTreg cells have recently been shown to be an essential non-redundant regulatory subset that supplements nTreg cells, in part by expanding TCR diversity within regulatory responses. Acute depletion of the iTreg cell pool in mouse models has resulted in inflammation and weight loss. The contribution of nTreg cells versus iTreg cells in maintaining tolerance is unknown, but both are important. Epigenetic differences have been observed between nTreg and iTreg cells, with the former having more stable Foxp3 expression and wider demethylation.
Healing from Trauma-Induced Memory Loss
Recovering from a traumatic experience can take days, weeks or even months. Memory loss can come back suddenly, but the underlying traumatic cause must be addressed for authentic healing. Everyone heals at their own pace, but if several months have gone by and your symptoms have not gotten better, then it may be time to seek professional help. It’s also a good idea to seek professional help if you:
* Have trouble functioning at home or work.
* Suffer from severe fear, anxiety or depression.
* Are experiencing terrifying memories, nightmares or flashbacks.
* Are emotionally numb and disconnected from others.
* Are avoiding things that remind you of the trauma.
* Are using alcohol or drugs to feel better.
If you fall into any of the categories above, then contact a trauma specialist today. A certified therapist can help you process the traumatic event and finally start healing your emotional trauma. You can also seek help with a center qualified in trauma treatment , where individualized plans with a variety of modalities can be employed to address your mental, emotional, physical and spiritual needs.
Under the care of a treatment facility, you’ll be able to work with a trauma specialist to process your trauma-related feelings and memories, stop the “fight or flight” response, learn how to control your emotions and rebuild your ability to trust other people. All of this will be done through a series of therapy sessions combined with emotional trauma treatments. Some of these treatments might include cognitive behavioral therapy, somatic experiencing and Eye Movement Desensitization and Reprocessing (EMDR). Cognitive behavioral therapy instills valuable coping mechanisms that can be used in times of stress. Somatic experiencing focuses on the body’s response to stress, as well as the brain’s response, to help unstick the traumatic event. And EMDR helps patients gain control over memories that are unpleasant or unwanted. In certain cases where someone also exhibits signs of depression or an anxiety disorder, antidepressant medication may be recommended as well.
Patients who have suffered memory loss due to physical trauma can sometimes benefit from surgery. After surgery, therapy is needed to help them recover their lost memories. Patients who suffer memory loss due to Wernicke-Korsakoff Syndrome should seek treatment right away at an alcohol rehab, where their substance abuse issues can be properly addressed.
If you are experiencing co-occurring PTSD and substance use disorder, it’s critical to seek treatment with a reputable dual-diagnosis facility. Instead of just treating one of the disorders, dual-diagnosis centers address both concerns equally. If your trauma has sparked a drug or alcohol addiction, you can’t separate the two—they are both enmeshed with each other and need to be worked on simultaneously. Both of the disorders can seriously and negatively affect your mind, body and spirit, so it can be helpful for your recovery to take part in complementary therapies such as acupuncture, yoga and tai chi that encourage positive goal-setting, expressiveness and a focus on whole-person health. Combined with therapy and medical treatments, this makes for a well-rounded program for healing.
Anyone who’s been through a traumatic experience knows that psychological, emotional and physical trauma hurt deeply. Start the journey to healing and find a way to stop the pain by calling a treatment facility today.
AP Biology Animal Form and Function Practice Test
A. is resting and has not eaten its first meal of the day.
B. is resting and has just completed its first meal of the day.
C. has not consumed any water for at least 48 hours.
D. has recently eaten a sugar free meal.
A. involves production of heat through metabolism.
B. is a term equivalent to cold blooded.
C. is only seen in insects.
D. is a characteristic of most animals.
A. the kidneys excrete salt into the urine when dietary salt levels rise.
B. the level of glucose in the blood is abnormally high whether or not a meal has been eaten.
C. the blood pressure increases in response to an increase in blood volume.
D. the core body temperature of a runner rises gradually from 37oC to 45oC.
time, he or she may die from water toxicity. ADH can help
prevent water retention through interaction with target cells in the
A. Secretin promotes an increase in the pH of the duodenum.
B. A hormone acts in an antagonistic way with another hormone.
C. A hormone is involved in a positive feedback loop.
D. A stimulus causes an endocrine cell to secrete a particular hormone, which decreases the stimulus.
A. peripheral nervous system
B. sympathetic nervous system
D. parasympathetic nervous system
A. the rising sun causes an increase in body temperature in a stationary animal.
B. an increase in body temperature results from exercise.
C. an increase in body temperature resulting from fever.
D. a decrease in body temperature resulting from shock.
A. cells need to be protected from nitrogen gas in the atmosphere.
B. feedback signals cannot cross through the interstitial fluid.
C. terrestrial organisms have not adapted to life in dry environments.
D. this prevents the movement of water due to osmosis.
A. more rapidly in myelinated than in non myelinated axons.
B. by the direct action of acetylcholine on the axonal membrane.
C. more slowly in axons of large than in small diameter.
D. by activating the sodium potassium pump at each point along the axonal membrane.
B. increased permeability of the collecting duct to water
C. reduced urine production
D. release of ADH by the pituitary gland
A. luteinizing hormone and oxytocin
B. oxytocin, prolactin, and luteinizing hormone
C. prolactin and calcitonin
D. follicle stimulating hormone and luteinizing hormone
A. a decrease in blood calcium increases the amount of the hormone that releases calcium from bone.
B. a nursing infant s sucking increases the secretion of a milk releasing hormone in the mother.
C. an increase in calcium concentration increases the secretion of a hormone that stores calcium in bone.
D. a decrease in blood sugar increases the secretion of a hormone that converts glycogen to glucose.
A. It primarily defends against fungi and protozoa.
B. It produces antibodies that circulate in body fluids.
C. It is responsible for transplant tissue rejection.
D. It protects the body against cells that become cancerous.
27. Leptin is a product of adipose cells. Therefore, a very obese mouse would be expected to have which of the following?
A. increased gene expression of db and decreased expression of ob
B. increased gene expression of ob and decreased expression of db
C. decreased transcription of both ob and db
A. inhibition of leptin receptors
B. overexpression of the leptin receptor gene
A. They are used to communicate between different organisms.
B. They are carried by the circulatory system.
C. They are modified amino acids, peptides, or steroid molecules.
D. They are produced by endocrine glands.
A. sensitive period in which canary parents imprint on new offspring.
B. addition of new syllables to a canary s song repertoire.
C. crystallization of subsong into adult songs.
D. renewal of mating and nest building behaviors.
A. altruism is always reciprocal.
B. natural selection does not favor altruistic behavior that causes the death of the altruist.
C. natural selection is more likely to favor altruistic behavior that benefits an offspring than altruistic behavior that benefits a sibling.
D. natural selection favors altruistic acts when the resulting benefit to the beneficiary, correct for relatedness, exceeds the cost to the altruist.
A. a voltage gated sodium channel.
B. a ligand gated sodium channel.
C. a voltage gated potassium channel.
D. a second messenger gated sodium channel.
A. oxygen used in mitochondria in one day.
C. carbon dioxide produced in one day.
D. water consumed in one day.
A. complement is secreted -> B cell contacts antigen -> helper T cell activated -> cytokines released
B. cytotoxic T cells -> class II MHC molecule antigen
complex displayed -> cytokines released -> cell lysis
C. self tolerance of immune cells -> B cells contact antigen -> cytokines released
D. B cell contact antigen -> helper T cell is activated -> clonal selection occurs
A. must include chemical senses, mechanoreception, and vision.
B. has information flow in only one direction: away from an integrating center.
C. has information flow in only one direction: toward an integrating center.
D. includes a minimum of 12 ganglia.
B. autonomic nervous system
C. sympathetic nervous system
D. parasympathetic nervous system
A. can produce diverse phenotypes that may enhance survival of a population in a changing environment.
B. guarantees that both parents will provide care for each offspring.
C. yields more numerous offspring more rapidly than is possible with asexual reproduction.
D. enables males and females to remain isolated from each other while rapidly colonizing habitats.
A. Prolactin is a nonspecific hormone.
B. Prolactin is an evolutionary conserved hormone.
C. Prolactin is derived from two separate sources.
D. Prolactin has a unique mechanism for eliciting its effects.
A. An individuals reproductive success depends in part on how the behavior is performed.
B. Some component of the behavior is genetically inherited.
C. The behavior varies among individuals.
D. In each individual, the form of the behavior is determined entirely by genes.
A. will not be able to interpret stimuli.
B. will not have a nervous system.
1. Tropomyosin shifts and unblocks the cross bridge binding sites.
2. Calcium is released and binds to the troponin complex.
3. Transverse tubules depolarize the sarcoplasmic reticulum.
4. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP.
5. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane.
A. much human behavior has evolved by natural selection.
B. human behavior is rigidly determined by inheritance.
C. the environment plays a larger role than genes in shaping human behavior.
D. humans cannot choose to change their social behavior.
A. an association area of the frontal lobe that is involved in higher cognitive functions
B. a region deep in the cortex that is associated with the formation of emotional memories
C. a central part of the cortex that receives olfactory information
D. a primitive brain region that is common to reptiles and mammals
A. stimulating the salivary glands.
B. accelerating heart rate.
C. relaxing bronchi in lungs.
D. stimulating glucose release.
A. Innate behaviors are expressed in most individuals in a population across a wide range of environmental conditions.
B. Genes have very little influence on the expression of innate behaviors.
C. Innate behaviors occur in invertebrates and some vertebrates but not in mammals.
D. Innate behaviors tend to vary considerably among members of a population.
A. The dog s behavior is a result of operant conditioning.
B. The dog has been classically conditioned.
C. The dog is performing a social behavior.
D. The dog is trying to protect its territory.
A. permitting passage only to a specific ion.
B. ability to change its size depending on the ion needing transport.
C. permitting passage by negative but not positive ions.
D. permitting passage by positive but not negative ions.
A. identify specific bacterial pathogens.
B. recognize differences among types of cancer.
C. identify specific viruses.
D. distinguish self from nonself.
A. the motor neuron fires action potentials but the skeletal muscle is not electrochemically excitable.
B. the motor neuron is considered the presynaptic cell and the skeletal muscle is the postsynaptic cell.
C. action potentials are possible on the motor neuron but not the skeletal muscle.
D. the motor neuron is considered the postsynaptic cell and the skeletal muscle is the presynaptic cell.
B. non shivering thermogenesis.
B. trial and error learning.
A. The neuron becomes less likely to generate an action potential.
B. The equilibrium potential for K (EK) becomes more positive.
C. The inside of the cell becomes more negative relative to the outside.
D. There is a net diffusion of Na out of the cell.
A. initiating signal transduction pathways in the cells.
B. causing molecular changes in the cells.
C. affecting ion channel proteins.
D. altering the permeability of the cells.
A. None of these schemes describes cross fostering.
B. You would see if curly whiskered mud rats bred true for aggression.
C. You would remove the offspring of curly whiskered mudrats and bald mud rats from their parents and raise them in the same environment.
D. You would place newborn curly whiskered mud rats with bald mudrat parents, place newborn bald mud rats with curly whiskered mud rat parents, and let some mud rats of both species be raised by their own species. Then compare the outcomes.
A. These proteins act individually to attack and lyse microbes.
B. These proteins are involved in innate immunity and not acquired immunity.
C. These proteins are one group of antimicrobial proteins acting together in cascade fashion.
D. These proteins are secreted by cytotoxic T cells and other CD8 cells.
A. they are necessary coenzymes.
B. only those animals use the nutrients.
C. only some foods contain them.
D. they cannot be manufactured by the organism.
A. forebrain and hindbrain.
B. central nervous system and peripheral nervous system.
D. sympathetic and parasympathetic.
A. Specialized regions are possible.
B. Extracellular digestion is not needed.
C. Intracellular digestion is easier.
D. Digestive enzymes can be more specific.
A. glial cell in the brain.
B. a neuron that controls eye movements.
D. a glial cell at a ganglion.
A. proteins that consist of two light and two heavy polypeptide chains
B. foreign molecules that trigger the generation of antibodies
C. proteins found in the blood that cause foreign blood cells
D. proteins embedded in B cell membranes
A. be bigger and stronger than the other animals.
C. have excess energy reserves.
D. be genetically related to the other animals.
A. sodium and potassium ions into the mitochondria.
B. sodium ions out of the cell and potassium ions into the cell.
C. sodium and potassium ions out of the cell.
D. sodium and potassium ions into the cell.
A. members of different populations differ in learning ability.
B. members of different populations differ in manual dexterity.
C. the cultural tradition of using stones to crack nuts has arisen in only some populations.
D. the behavioral difference is caused by genetic differences between populations.
C. coordinating limb movement.
A. antigen receptors are not the same as for a flu virus to which she has previously been exposed.
B. no memory cells can be called upon, so adequate response is slow.
C. it takes up to two weeks to stimulate immunologic memory cells.
D. specific B cells and T cells must be selected prior to a protective response.
A. clotting proteins migrating away from the site of infection
B. reduced permeability of blood vessels to conserve plasma
C. increased activity of phagocytes in an inflamed area
D. release of substances to decrease the blood supply to an inflamed area
D. sensory neuron dendrites.
A. Only target cells are exposed to aldosterone.
B. Aldosterone is unable to enter nontarget cells.
C. Nontarget cells convert aldosterone to a hormone to which they do respond.
D. Nontarget cells destroy aldosterone before it can produce its effect.
A. is aimed at attracting mates.
D. is the final song that some species produce.
A. The sound from the earphone irritates the male mosquitoes, causing them to attempt to sting it.
B. The males learn to associate the sound with females.
C. Through classical conditioning, the male mosquitoes have associated the inappropriate stimulus from the earphone with the normal response of copulation.
D. Copulation is a fixed action pattern, and the female flight sound is a sign stimulus that initiates it.
A. is the point of separation from a living from a dead neuron.
B. is the minimum hyperpolarization needed to prevent the occurrence of action potentials.
C. is the minimum depolarization needed to operate the voltage gated sodium and potassium channels.
D. is the peak amount of depolarization seen in an action potential.
A. positive feedback benefits the organism, whereas negative feedback is detrimental.
B. the effector s response in positive feedback is in the same direction as the initiating stimulus rather than opposite to it.
C. the effector s response increases some parameter (such as temperature), whereas in negative feedback it decreases.
D. positive feedback systems have control centers that are lacking in negative feedback systems.
A. the movement of sodium and potassium ions from the presynaptic into the postsynaptic neuron.
B. impulses ricocheting back and forth across the gap.
C. impulses traveling as electrical currents across the gap.
D. the movement of calcium ions from the presynaptic into the postsynaptic neuron.
A. Classical conditioning involves trial and error learning.
B. Imprinting is a learned behavior with an innate component acquired during a sensitive period.
C. Associative learning involves linking one stimulus with another.
D. Operant conditioning involves associating a behavior with a reward or punishment.
A. All of the above are equally productive ways to approach the question.
B. bring animals into the laboratory and determine the conditions under which they become restless and attempt to migrate.
C. perform within population matings with birds from different populations that have different migratory habits. Rear the offspring in the absence of their parents and observe the migratory behavior of offspring.
D. observe genetically distinct populations in the field and see if they have different migratory habits.
2 Models and Methods
2.1 The Model
In this section, we introduce the model for continuous firing-rate neurons, derive a mathematical reduction for sparsely coded memories, and discuss the mean-field approximation corresponding to the limit of infinitely many neurons.
2.1.1 Model Equations
2.1.2 Reduced Model
The system in equation 2.6 is a reduction of the original system in equation 2.3. The number of equations in the reduced system depends on the particular realization of the network (i.e., on ). In principle, the system has equations, as is the number of possible populations, but in practice, due to the finite size of the network and its sparse coding controlled by the sparsity , there are many fewer populations as for many 's. The total number of equations in the system depends on and but will always be fewer than , tending to only for very large . Remarkably, in this framework, for and , we are able to simulate a network of neurons with 1000 population currents.
2.1.3 Mean-Field Equations
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2.2 Nested Memory States
The dynamical system defined in equations 2.5 and 2.6 is a nonlinear system with variables. There is no approach that guarantees finding all the fixed points of such a system. Our approach is to define a specific and meaningful set of solutions that can be fully analyzed in the mean-field limit of equations 2.8 and 2.10. We define a -intersection state to be a state where only neurons encoding all memories in a given set of memories are active, where is a number between 1 and . For this is a single memory, while for , it is the intersection between two memories and so on. These are nested memory states since a -intersection includes intersections.
2.2.1 Fixed-Point Solution for a Q-Intersection State
The solution for is obtained in a corresponding area of existence, and for this solution, it is possible to address the conditions of stability. As these conditions depend on the transfer function, from now on, we will show results for . This function has the property of having a threshold activation and being sublinear. Both properties are important for the purpose of analyzing the existence and stability of the solutions.
2.2.2 Region of Existence of Q-Intersection State
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From the analysis, we can see that for , the first condition of an ansatz (see equation 2.17) is satisfied for all values of and , whereas the second condition about nonactive currents is not always satisfied and defines the region of existence of the fixed-point solution. For instance, equations 2.19 and 2.20 define the condition of the existence of the solution that active currents must be above threshold and inactive ones below threshold. The boundaries of existence do not depend on the number of memories that are stored in the network, only on the number of memories that take part in the intersection.
2.2.3 Region of Stability of Q-Intersection State
2.3 Numerical Methods and Implementation Details
The problem of finding stable states of the system, equations 2.7 to 2.9, reduces to finding fixed points of the equations and calculating their stability as shown above. To find solutions to the system that cannot be computed analytically, we employ numerical algorithms. In the regions of multistability, the convergence of the algorithm depends on the initial conditions. In order to find different solutions, we performed many runs of network dynamics, initializing the algorithm at random points. After the stable fixed solution is found, a continuation method is used to find the solution for the next pair of parameters . We used this technique also to validate analytical results.
Unless specified, otherwise all the results shown are for a network of infinitely many neurons (in the meaning highlighted in section 2.1.3). The sparsity is , the time constant of the neurons , the threshold , and the gain function . The value of used to generate the results shown in Figures 2, 3, and 4 is .
Brain “ripples” experience into memories when you sleep, study shows
Sleep might play a much more central part in memory formation, new research reveals. Sleeping allows two different brain regions involved in the process to communicate and sync.
This paper draws on previous research by the study’s senior author György Buzsáki, M.D., Ph.D. and Biggs Professor of Neuroscience at the New York University. It focuses on the hippocampus, a brain structure suspected to take part in forming permanent memories during sleep. Dr. Buzsáki found that neurons in the hippocampus fire in high-frequency bursts of activity (which he christened “ripples”) during sleep, suggesting the cells were indeed involved in memory formation.
Now, a team led by Buzsáki wants to delve deeper into the backstage of human memory.
The team invented a novel brain imaging technology, the NeuroGrid, to use in their study. It consists of a collection of tiny electrodes linked together to form a sheet, that is then laid across an area of the brain. Each electrode will then continuously monitor the activity of a set of neurons, allowing the team to take a wider but highly detailed snapshot of activity in the brain.
“This particular device allows us to look at multiple areas of the brain at the same time,” said Jennifer Gelinas, M.D., Ph.D., assistant professor at Columbia University and co-first author of the paper.
Using this electrode grid (which was supplemented with additional tracking neurons implanted in deeper areas of the brain,) the team examined neural activity in several parts of rats’ brains during NREM (non-rapid eye movement) sleep, the longest stage of sleep.
(A) Micrograph of a large-scale NeuroGrid (scale bar 1.5 mm, inset scale bar, 1 mm). (B) Signal sample acquired from multiple cortical areas and hippocampus using the grid and a silicon probe (H). Includes somatosensory (S), midline (M), posterior parietal (PPC), and visual (V) cortices and hippocampal area CA1 (H). Shaded boxes illustrate delta (blue), spindle (yellow), and gamma (green) as well as cortical and hippocampal ripple (purple) oscillations.
Image credits Dion Khodagholy et al., 2017, Science.
The team first confirmed the existence of the ripples Buzsáki identified in the hippocampus during sleep and also found them in certain areas of the association neocortex, a brain region involved in processing complex sensory information. A surprising find was that the ripples seemed mirrored throughout the brain, occurring in the association neocortex and hippocampus at the same time. This suggests that the two regions communicated as the animals slept.
The association neocortex has been tied to memory storage, so the team believes that this dialogue between the two structures helps the brain retain information.
Anatomical map of ripple occurrence relative to the somatosensory and visual cortex in a sample rat. Raw sample traces are shown on the left. Regions where over 0.05 ripples were recorded per second are shown in red.
Image credits Dion Khodagholy et al., 2017, Science.
Finally, to put their theory to the test, the team trained one group of rats to locate rewards in a maze. A control group was set up, whose rats would also try to explore the maze for treats, but without any prior training — i.e. they would explore in a random fashion, without any prior memory of the maze’s layout or treat location. Afterwards, the scientists used their initial method to examine the brain activity of both groups during NREM sleep.
In the control group, these ripples in the hippocampus and cortex remained relatively constant before and after the exploration task. For the trained group, however, they report increased cross-talk between the two brain areas as well as greater synchronization (coupling) of the ripples. A second training session increased communication even more, lending weight to the hypothesis that it is fundamental to the creation and storage of memories.
“Hippocampal-PPC [posterior parietal cortex] ripple coupling increased during postlearning sleep compared to postexploration sleep, a trend that was consistent across all six trained rats,” the authors note.
“Furthermore, multiple consecutive sessions of exploration in the control rats did not induce a change in hippocampal-PPC ripple coupling, and these coupling values were significantly less than those in trained rats.”
In the future, the team hopes brain surgery patients will allow them to use the NeuroGrid to check if the same ripples form in the human brain. Another avenue of research will be to see if altering these signals in animal brains can suppress (or maybe boost) memory formation and storage — which would confirm that the ripples underpin these processes.
“Identifying the specific neural patterns that go along with memory formation provides a way to better understand memory and potentially even address disorders of memory,” Dr. Gelinas concluded.
The paper, titled “Learning-enhanced coupling between ripple oscillations in association cortices and hippocampus” has been published in the journal Science.
Astrocytes are the star-shaped supporting cells present in the brain and spinal cord. They are the most abundant and diverse glial cells present in the CNS.
They are the star-shaped cells having a central body
with radiating protoplasmic processes. They may be protoplasmic or fibrous in
Protoplasmic astrocytes have abundant organelles and small branching protoplasmic processes. They are abundantly present in the grey matter.
Fibrous astrocytes have large unbranched protoplasmic processes. They have limited organelles and are abundantly present in the white matter of CNS.
Like other cells of the CNS, they are also derived
from the neuro-epithelium of the neural tube.
Astrocytes perform a number of functions that are essential for the normal functioning of neurons. These include:
- Regulation of ionic concentration
- Providing nutrients to the neurons
- Removing the metabolites and waste
- Contributing in the blood-brain
- Repair of the CNS
- Regulation of blood flow
- Physical support to the developing
- Synapse structure and functioning
- Formation of glial limiting membrane
The pathologies of astrocytes include astrocytomas,
the most abundant tumors of the brain.
They also include other diseases such as Alzheimer’s disease and Alexander’s disease, etc as well as some developmental disorders of the CNS.