Chapter 13 questions
At the cellular level, the brains of Alzheimer's patients are found to contain three characteristic changes:
1 Patches of amyloid plaques, made up of a substance called beta-amyloid 2 Whorls of neurofilaments called neurofibrillary tangles 3 Loss of the basal forebrain neurons that normally secrete the neurotransmitter acetylcholine
Iconic memory,
A few seconds at most, Fleeting impression of an image that flashes on the television for only an instant.
Cells can influence each other's development via cell-cell interactions, in which a cell differentiates based on what neighboring cells are doing.
A possible treatment for neurodegenerative disease includes placing undifferentiated cells, called stem cells, into the brain region that has degenerated. These cells would then differentiate into neurons appropriate for that region.
Methylation of the glucocorticoid receptor gene in rodent pups with inattentive mothers was found to enhance the stress response for the whole of the pups' lives.
A similar mechanism may apply to humans; this same gene is found to be methylated in the (postmortem) brains of suicide victims that were subjected to childhood abuse more often than it is in controls.
Classical conditioning involves the pairing of a stimulus with some other neutral stimulus (such as a bell).
After numerous such pairings, the previously neutral stimulus predicts the second stimulus. Experimental evidence in lab animals and a PET study in humans confirmed that the cerebellum is(are) crucial for simple eye-blink conditioning. In operant conditioning, a link is formed between a behavior, such as bar-pressing, and a reaction, such as the arrival of food. If the reaction is rewarding, the propensity to engage in the behavior increases.
It is now clear that deficits like Henry Molaison's cannot be ascribed solely to removal of the lateral temporal cortex, including the hippocampus, and impairment is not the result of loss of all verbal memory skills.
After several days of practice, patients like Henry show improvements on mirror-reading tests, which deal with verbal material.
The production of nerve cells is called neurogenesis.
Although neurons themselves do not divide, the cells that become neurons reproduce through a process called mitosis and form a closely packed zone of cells called the ventricular zone inside the neural tube.
At present, the definitive diagnosis for Alzheimer's disease is made by autopsy.
An innovative approach is to use Pittsburgh Blue dye, which can reveal beta-amyloid. A possible treatment strategy is to develop drugs that interfere with enzymes that favor beta-amyloid production. Alternatively, risk for Alzheimer's disease can be reduced by physical activity, mental activity, adequate sleep.
Studies of environmental influences on the brain have shown that the brains of animals from enriched conditions have enhanced cholinergic activity throughout the cortex compared to animals from impoverished conditions.
Animals from enriched conditions have heavier, thicker cortices. Animals from impoverished environments have All of the above. Animals from enriched conditions have more hippocampal neurons. Animals from enriched conditions show enhanced recovery from brain damage.
Within a week of conception, the emerging human embryo shows three distinct cell layers. The nervous system develops from the outer layer, called the ectoderm. As the cell layers thicken, they grow to form a groove.
At the anterior end of this groove, a thickened collection of cells form, and three subdivisions become apparent. These subdivisions correspond to the future forebrain (cortical regions, thalamus, and hypothalamus), midbrain, and hindbrain (cerebellum, pons, and medulla). The interior of the neural tube becomes the All of the above. By the end of the 8th week of embryonic life, rudiments of all major organ systems are apparent, and the head is about 50% of the total mass of the embryo. After 10 weeks, the embryo is called a(n) fetus.
In the hippocampus of rats, place cells are neurons whose rate of firing increases when a rat is in, or moving toward, a particular space.
Bird species that hide food in many locations have a larger hippocampus than other bird species have.
The experiments with monkeys, together with Henry's case, indicate that we need at least one intact medial temporal lobe, including the hippocampus, in order to make new declarative memories.
But the hippocampus isn't the only brain structure needed for new declarative memories. Damage to the mammillary bodies can also cause amnesia.
Salivation of the dog in response to the bell:
Conditioned response
The neutral stimulus to be learned (in this case, a bell):
Conditioned stimulus
All of the cells in the human body have a complete copy of the individual's genotype.
Each cell uses only a small subset of these genes to form proteins. This process is called gene expression. The study of the factors that influence this process is called epigenetics.
Estimates suggest that there are about 100 billion neurons in the human brain.
Each neuron develops thousands of synapses, and in the end, the brain contains a staggering 100 trillion synaptic connections!
Memory traces, records laid down in memory, deteriorate due to interference from events prior to or after their formation.
Each time a trace is activated, new aspects may be added to the trace, which are then recalled along with the original trace. False memories can be created this way.
As people age, NMDA receptors decrease at the same rate as normal memory loss in adults.
False
Low glutamate diets are correlated with poor learning in children.
False
Neuroimaging studies have detected more NMDA receptors in the brains of young adults after learning has occurred.
False
Henry Molaison was able to retain a normal amount of information.
He could remember and repeat it normally until he was distracted by something else, after which he did not recall being given an item to remember.
Priming does not appear to require declarative memory of the stimulus.
Henry Molaison and other patients with amnesia exhibit priming for words, indicating that this form of learning requires mechanisms in None of the above. In functional-imaging studies, perceptual priming (priming based on the visual form of words) is related to reduced activity in bilateral occipitotemporal cortex, while conceptual priming (priming based on word meaning) is associated with reduced activation of the left frontal cortex.
If you learn a list of words, the likelihood that you will recall those from the beginning of the list is called the primacy effect, and the likelihood that you will recall those at the end of the list is called the recency effect.
Henry Molaison would have exhibited a recency effect, but not a primacy effect.
At a glutamatergic synapse of the sort found in the hippocampal formation, moderate amounts of activity will cause activation of only the postsynaptic AMPA receptors. In this condition, NMDA receptors are blocked from mediating a response to the glutamate by the presence of Mg2+ ions, which act like a cork, blocking the Ca2+ channel in the receptor.
If large amounts of glutamate are released, however, the action of the AMPA receptors depolarizes the postsynaptic membrane enough to dislodge the Mg2+ "corks," allowing the NMDA receptors also to respond to the glutamate. This results in the opening of the NMDA channel and the influx of a large number of Ca2+ ions. The large influx of Ca2+ then activates a variety of intracellular enzymes that affect AMPA receptors in several important ways. So, we can say that the NMDA receptor is both voltage-gated and ligand-gated—both conditions must be present in order for the receptor to be fully active.
Patients with posttraumatic stress disorder may be caught in a cycle in which their remembering the original trauma produces a stress hormone response, causing release of epinephrine, which strengthens the existing memory and causes it to become more likely to be reexperienced.
It has been proposed that treating people with antiadrenergic drugs either before or immediately after the trauma may prevent the development of PTSD by eliminating the potentiating effects of these hormones on memory.
Memory information that we are aware of accessing—facts, words, and so on—is referred to as declarative memory.
It is assessed using explicit tests, and in general it is concerned with the "what" questions of memory. Learning that is not subject to conscious recall, such as riding a bicycle, is called nondeclarative memory, and it is examined using implicit tests; in general it is concerned with the "how" questions of memory.
Long-term memory,
May last for years, The name of the street on which you grew up.
Memory retrieval refers to access to memories stored in LTM.
Memory consolidation refers to the transformation of a memory trace into long-term storage. Memory encoding refers to passage of raw sensory information into short-term storage. The medial temporal lobe seems to be crucial for moving information from STM into LTM. An intact hippocampus is necessary for consolidation of declarative STMs into LTMs.
There is now evidence of adult neurogenesis in the dentate gyrus of the hippocampal formation. The new neurons integrate into the functional circuitry there and play a role in forming new memories.
Neurogenesis also appears to enhance fear conditioning and spatial memory. Apoptosis is the developmental process during which "surplus" cells die. Neurons compete for synaptic sites and access to a chemical, called neurotrophic factors, that the target structure makes and releases. Cells that do not create enough synapses or do not get enough neurotrophic factors soon die.
All three kinds of memory skills (i.e., sensorimotor, perceptual, and cognitive) appear to be impaired in people with damage to the basal ganglia.
Neuroimaging studies have shown the importance of this structure along with the motor cortex and the cerebellum for sensorimotor skill learning.
The three forms of nondeclarative learning are skill learning, priming, and conditioning.
Of these, the mirror-tracing task is an example of skill learning. Altered processing of a stimulus as a result of previous exposure to stimuli reflects priming.
At the gross anatomical level, the brains of Alzheimer's patients show pronounced cortical atrophy, especially in the frontal, temporal, and parietal cortex.
PET scans reveal a marked decrease in metabolism, especially in the posterior parietal and temporal regions.
N.A.'s symptoms are similar to those of Henry, featuring normal short-term memory, impaired long-term memory, and preserved ability to form nondeclarative memories.
Patient N.A. suffered damage to the dorsomedial thalamus and to both mammillary body(ies) from an accident with a miniature sword. N.A. is profoundly amnesic, mostly for verbal learning. This amnesia is primarily anterograde in nature.
Patient K.C.'s left frontoparietal cortex and right parieto-occipital cortex were damaged in a motorcycle accident.
Scans indicated that the volume of his hippocampus and nearby cortex were markedly reduced. K.C.'s episodic memory was completely lost, and he was unable to form new memories of that sort. K.C.'s existing semantic memory was intact, and with care he could form new memories of this sort.
Choose the most appropriate example for each type of declarative memory:
Semantic memory: generalized declarative memory. Episodic memory: autobiographical knowledge
One experimental paradigm presented long sequences of pairs of slides, one of which was new and one of which was seen in the previous presentation.
Subjects were able to identify the previously seen slide with great accuracy, even when as many as 10,000 such items were presented. The researcher concluded that, for all practical purposes, there seems to be no limit to memory capacity.
In rabbit eye-blink conditioning, the CS consists of a tone, the US consists of a puff of air, and the CR consists of a blink. Information about the US and CS converge in the cerebellum.
The rabbit soon learns to blink upon presentation of the CS. The basic reflex controlling the behavior has a simple circuit: sensory afferent fibers project from the cornea to the nucleus of the trigeminal cranial nerve, and motor fibers activate the closing of the eyelids.
Research has shown that a tiny dose of epinephrine injected directly into the amygdala of rats enhances memory formation.
The tendency to remember an emotionally arousing story significantly better than a closely matched but emotionally neutral story can be countered by treatment with propranolol. This drug seems to interfere with the ability of adrenal stress hormones to enhance memory.
The frequency of Alzheimer's increases with aging up to age 85-90. People who reach 90 without symptoms become increasingly less likely to develop Alzheimer's.
This indicates that Alzheimer's is a disease. Remaining physically and mentally active reduces the risk of developing Alzheimer's.
Some synapses, formed early in development, are later retracted. This synaptic rearrangement typically takes place after a period of apoptosis. For example, approximately 50% of spinal motoneurons that form die later.
This process is seen in other neural regions, as well. In the human cerebral cortex, there is a net loss of synapses from late childhood until midadolescence. This synaptic remodeling is evident in thinning of the cortical gray matter as pruning of dendrites and axon terminals progresses. The thinning process proceeds in a(n) posterior to anterior direction, with the prefrontal cortex thinning last.
Episodic memory was assessed by having subjects listen to autobiographical passages or passages written by others during brain imaging.
This study revealed greater activation of the right frontal and temporal lobes when listening to the autobiographical passages than to other people's stories. This suggests that autobiographical and semantic memories are processed and stored in different parts of the cortex.
Drug treatments that interfere with LTP interfere with learning and memory.
True
The time course of LTP is similar to the time course of memory formation.
True
Training an animal on a learning task induces LTP in the animal's brain.
True
Salivation of the dog in response to the meat powder:
Unconditioned response
Meat powder placed in the dog's mouth:
Unconditioned stimulus
Habituation is a simple form of nonassociative learning. In short-term habituation of the gill-withdrawal reflex in Aplysia, the siphon is stimulated repeatedly with a jet of water, which causes the withdrawal of the gill.
Upon repeated administration(s) of the jet, the withdrawal reflex is diminished because of decreased release of neurotransmitter in the synapse between the sensory cell and the motoneuron. This is known as short-term habituation. If testing occurs over a series of days, long-term habituation occurs, in which case the number of synapses decreases.
Short-term memory,
Variable—some researchers limit this type of memory to 30 seconds in humans, others define it as up to a few hours, Keeping a phone number in your memory long enough to place a call.
Plastic changes at synapses can be physiological or structural.
When the amount of neurotransmitter released changes, or the sensitivity of postsynaptic receptors change, a physiological change has occurred. When a neural circuit that is used more often increases the number of synaptic contacts it makes, a structural change has occurred.
Presynaptic changes are seen in long-term potentiation.
When the postsynaptic cell is strongly stimulated, an intracellular process causes the postsynaptic cell to release a retrograde transmitter. This travels back across the synapse and induces the presynaptic terminal to more glutamate, thereby strengthening the synapse even more.
Learning is the process of
acquiring new information, and memory is the ability to store and retrieve that information.
Neurogenesis is the
birth of new neurons from nonneuronal cells.
Methylation:
chemical modification of DNA that suppresses expression of genes
Tower of Hanoi problem and other tasks involving planning:
cognitive skill
Synaptogenesis is the
establishment of connections between neurons and other cells.
Memory involves changes in the
functioning of synapses and circuits due to neuroplasticity, and varied experiences and learning cause the brain to change and grow.
In a study of healthy, cognitively normal 55-87 year olds,
hippocampal volume was the only brain measure that correlated with delayed recall scores.
Synapse rearrangement refers to the
loss of some synapses and formation of others.
Cell migration refers to the
massive movement of nerve cells to new locations.
Reading reversed text:
perceptual skill
Phenotype:
physical characteristics, determined by the interaction of an individual's genes and environmental variables
The form of amnesia called
retrograde amnesia is common after brain trauma and results in the loss of memories formed up to a year before the injury. However, after his surgery, Henry Molaison lost the ability to form new memories, a condition known as anterograde amnesia. Henry was unable to store new information for more than a few minutes. His surgeon had removed the amygdala and most of the hippocampus from both hemispheres of his brain.
Neuronal cell death refers to the
selective demise of many neurons.
Mirror tracing:
sensorimotor skill
Long-term potentiation (LTP) is a
stable and enduring increase in the magnitude of the response of neurons after presynaptic neurons have been stimulated by bursts of high-frequency electrical pulses (called a tetanus). Put simply, "cells that fire together wire together."
Spiegler and Mishkin's experimental task involving recognition of an object (in a pair of objects) that has been seen before is called
the delayed non-matching-to-sample task. Their studies demonstrated that medial temporal lobe damage particularly impairs declarative memory in monkeys.
Human case studies, along with animal research, has clearly shown that a brain circuit that includes
the hippocampus True, the mammillary bodies True, the corpus callosum False, the pituitary gland False, and the dorsomedial thalamus True is needed to form new declarative memories. But these case studies also clearly show that established declarative memories, formed before brain damage, are not stored in these structures. If the memories were stored there, they would have been abolished when the structures were damaged.
Korsakoff's syndrome is caused by a
thiamine deficiency. The disease is especially prevalent in people who abuse alcohol. These patients exhibit amnesia and fill in gaps in their memory with false information, a process called confabulation. Korsakoff's patients often fail to recognize or sense any familiarity with some items, even when repeatedly presented, and frequently deny that anything is wrong. Degenerative damage to the dorsomedial thalamus and the mammillary bodies is commonly seen in these individuals.
Genotype:
total genetic information carried in an individual's cells
Cell differentiation is the
transformation of new cells into distinctive types of neurons or glial cells.
Henry Molaison, known as "patient H.M.," suffered from
uncontrollable seizures, leading doctors to recommend brain surgery, in which the surgeons removed large portions of his anterior temporal lobes.
