Learning and memory Flashcards
What does it mean for neural pathways to be hardwired?
these are neural pathways
that establish connections during development that subsequently remain unaltered. the generic term for those processes that ensure the pathway is properly connected is specificity.
Which neural pathways are referred to as plastic?
pathways subject to continual re-wiring, either during development or as a result of experience, are referred to as plastic, and the re-wiring processes described as plasticity.
What is developmental plasticity?
It is wiring that is conditional on early sensory experience and shapes subsequent perception.
What is learning?
it is also plasticity and is the acquisition of reproducible alterations in behavior as a result of particular experiences. The storage of
the altered behavior over time is memory.
How can learning and memory be tested operationally in animals?
by recall, in which the previously learned behavior is elicited by the appropriate stimuli.
What is declarative (explicit) memory?
It is memory for facts. Declarative learning is fast, it requires few trials, requires conscious recall, and may be readily forgotten. It has two components that are dissociable in patients with cortical damage.
What is episodic (recollection) memory?
It is memory for specific events, in which associations are established at a specific time and place
What is spatial navigational learning?
It is an extensively studied example of episodic learning. It is the ability of rats
to navigate through a maze in which they must learn to associate their positions in the maze with cues in their surroundings.
What do the extensive connections of the medial temporal lobe allow in terms of episodic memory?
to act as a convergence zone for the different information streams. The different components of an episodic memory are distributed across disparate regions of the brain and must be bound together for recall of the episode.
What is semantic (familiarity) memory?
it is a component of declarative memory. is memory of facts unrelated to events; that Bali is an Indonesian island can be recalled without ever having been there, so semantic memory is about “knowing that.”
How are semantic memories sorted?
sorted into categories (sets of related objects), which appear to be stored in different areas of brain. Recall of specific items seems to need activation of multiple brain sites, each of which codes for a given attribute (e.g., color, function, name) of the item.
What is procedural (implicit) memory)?
memory is memory for skills, such as learning to walk. It is “knowing how” memory. Procedural memory is slow, it needs many trials and it is incremental in that improvement occurs gradually over time. Performance of procedural tasks does not involve conscious recall. For this reason procedural memory (like emotional memory) is described as implicit memory. Once established, procedural memories are not forgotten even after many years without rehearsal.
Declarative memory has at least two phases categorized by their time course. What is Working memory (short-term memory)?
It is temporary, limited in capacity and requires continuous rehearsal to keep it.
What is Long-term (remote) memory (LTM)?
It is, if not permanent, at least long-lasting, has no obvious upper limit to its capacity and does not require continual rehearsal.
Amnesias (loss of memory) due to brain damage can affect working memory and LTM independently. What are the two types of LTM?
It depends on whether memories are lost for
events and facts acquired before, retrograde amnesia, or after, anterograde amnesia, the brain damage.
What is consolidation?
is the process that makes both declarative and procedural memories increasingly resistant to disruption or interference from similar learning over time.
How does consolidation of memories occur?
Serial models postulate that elements may be selected from working memory for consolida-
tion into LTM by attention and arousal mechanisms. Experiments in which animals are injected shortly after training on a novel task with antibiotics which inhibit protein syn-
thesis show that consolidation requires protein synthesis.
What is interference?
recalling a consolidated memory returns it to a labile state in which it becomes sensitive to interference. This is where a previously established memory can no longer be retrieved because of competition from new learning.
How is interference prevented?
the recalled memory must now be reconsolidated. For example, if established auditory fear memories are reactivated in rats, protein synthesis is required for the memory to be retained.
Procedural memory is learning to produce a motor response to a particular input. It is
divided into two types; nonassociative and associative, what is non-associative?
occurs in response to only a single kind of stimulus. Two examples are habituation, in which repeated exposure to a weak stimulus results in a reduction or a loss of the response normally seen with occasional presentation of the stimulus, and sensitization, which is an exaggerated response to innocuous stimuli following a strong noxious (unpleasant) stimulus
What is associative learning?
it learning needs the pairing of two different types of stimulus within a short time and in the correct order. It enables animals to behave as if they can predict relationships of the kind: if A then B.
What is classical conditioning characterised by?
temporal contiguity, the requirement that the CS must be presented before the US, and contingency, that animals learn that a predictive relationship exists between the CS and the US.
When does extinction of a conditioned response occur?
It occurs if the CS is repeatedly presented without the US or if the temporal pairing of the CS and US is disrupted (i.e., if they are presented randomly). Extinction is not the same as forgetting. If after extinction the pairing of CS and US is restored the CR returns much more rapidly than it does in naive animals.
What is aversive conditioning?
It is classical conditioning in which the US is noxious and which results in fear responses to normally neutral stimuli
What is operant (instrumental) conditioning?
an animal learns an association between a
motor activity it performs (e.g., pressing a lever) and the arrival of a stimulus, termed the reinforcer (e.g., a food pellet). Reinforcers may be positive, in which case they increase
the probability that an animal will act to obtain it, or negative (an aversive stimulus, such as an electric foot shock) in which case the animal will work to avoid it. Operant conditioning is used to investigate motivated behaviors.
What modulates the likelihood of specific memories being consolidated?
The arousal levels associated with an event. The arousal signals to which the brain memory circuits respond are adrenal hormones (both catecholamines and steroids), and several CNS peptide neurotransmitters released in response to stress.
what is the evidence of the involvement of catecholamines in memory circuit?
● Enhanced recall of emotionally neutral learning tasks by noradrenaline (norepinephrine) or adrenaline (epinephrine) given within a short time of the learning trials.
● No better recall of an emotionally charged version of a story compared with the neutral
version after administration of the b-adrenoceptor antagonist propranolol.
People with higher levels of sympathetic activity are more likely to suffer from post-traumatic stress disorder after a traumatic experience.
What is the shape of catecholamine-dose-response curve?
has an inverted U shape; moderate concentrations are more effective enhancers of memory than either high or low levels.
How do catecholamines exert their effect on memory?
neither of these hormones crosses the blood–brain barrier their actions on the CNS must be exerted. The catecholamines act at b-adrenoceptors on visceral afferents that run in the vagus (X) nerve to the nucleus of the solitary tract. This results in activation of noradrenergic neurons of the locus coeruleus that are part of a brain arousal system. This system projects to the amygdala and hippocampus to modulate learning.
How do glucocorticoids released by activation of the hypothalamic–pituitary adrenal axis in stress have effects on learning and memory?
These hormones readily cross the blood–brain barrier to act on steroid receptors that are located in high density in the amygdala and hippocampus. Low doses of glucocorticoids enhance, while high doses (or chronic exposure in long-term stress), impairs memory. Low concentrations occupy the high-affinity mineralocorticoid receptors (MR) and this facilitates strengthening of synapses thought to be crucial for learning. In contrast, high glucocorticoid concentrations fully saturate the low-affinity glucocorticoid receptors (GR) and this blocks the synaptic strengthening necessary for learning.
The anterior pituitary corticotrophs manufacture, from a single precursor, adrenocorticotrophic hormone (ACTH) and the opioid peptide, b endorphin, enkephalins are released by adrenal medulla, what is their effect on memory?
both of which impair learning by direct action on the CNS. Enkephalins, also opioid peptides, are co-released impair memory by a peripheral action. Naloxone, an antagonist of opioid receptors facilitates memory.
Cholinergic enhancement of memory is well documented. Muscarinic receptor antago-
nists impair memory, while inhibitors of acetylcholinesterase improve it. What is the mechanism of this?
Acetylcholine modulation of memory is mediated by the septohippocampal pathway and the cholinergic nuclei of the basal forebrain. The amygdala may enhance consolidation by activating the cholinergic attentional system in the basal forebrain.
Working memory (WM) is an on-line memory system. On average how many items can the working memory hold?
up to four items simultaneously in WM, though there are individual differences. EEG, brain imaging, and behavioral studies all suggest that the number of items that can be held is unaffected by the complexity of the items. Hence, the capacity of WM seems to be defined by the number of items rather than the total quantity of information.
What is the discrete resource model?
argues that any item represented in WM must be assigned to one of a limited number of slots.
What is the flexible resource model?
each item is assigned a share of WM resources and that performance is limited for large numbers of items because each item gets only a small share of WM resources.
How does interference between representations held in WM occur?
If items to be remembered are similar to those being processed, accuracy of recall is reduced. Delaying recall has little effect on recall accuracy so a simple decay model, in which item storage in WM fades over time, cannot be the case.
Which cognitive skills is WM capacity positively correlated with?
reading comprehension, problem-solving ability, maintaining attention in the face of distractions.
What is the phonological loop?
allows speech sounds to be held and rehearsed for long enough to give continuity to spoken language, so that phrases and sentences can be comprehended. It requires the left cerebral hemisphere.
What is the visuospatial sketch pad?
temporary store for visual, spatial, and kinesthetic input that brain imaging indicates involves several regions in the right hemisphere
What are the slave systems?
The phonological loop and visuospatial sketchpad are together referred to as slave systems.
What is the proposed interface between LTM and slave systems?
An episodic buffer via the central executive, which binds information from a variety of sources into coherent episodes. The contents of the episodic buffer are assumed to be consciously retrievable through activity of the central executive.
Other than binding information into coherent episodes, what is the central executive also involved in ?
The executive is also postulated to mediate directed attention, which transfers information into the episodic buffer from the slave systems and LTM where it can used to create new cognitive representations and for problem solving. The central executive may plan how to execute complex cognitive activities.
What is the prefrontal cortex involved in?
complex problem solving and planning future actions and there are good reasons for supposing that these executive tasks require working memory
How does the connectivity of the prefrontal cortex argue for its role in working memory?
Firstly, there are reciprocal connections between the PFC and other cortical areas, so the PFC receives visual, auditory, and somatosensory information. Secondly, the PFC is interconnected with the medial temporal lobe and dorsomedial thalamus that have a well-documented role in learning and memory. Thirdly, the PFC is a component of the executive thalamocortical-basal ganglia circuit which allows it to modulated by reward and salience.
What is the evidence for specific subsystems of working memory in the PFC?
Recording from the PFC in alert behaving monkeys reveals cells that fire in predictable ways during delayed-response tasks. For example, many cells fire throughout the delay period, others fire when the food is placed in the location and when the animal is allowed to choose the location. Particular regions of the PFC seem to be modality-specific
Which lobe is critical for declarative learning?
The medial temporal lobe and its connections with the hypothalamus and thalamus
What do bilateral lesions of the hippocampus, even when confined to the selective loss of pyramidal cells from just one region, result in?
an anterograde amnesia so extreme that patients are no longer able to form new long term memories. Working memory and procedural memory are unharmed, as are remote long-term memories, although some retrograde amnesia is seen.
Lesions to the medial temporal lobe have shown anterograde amnesia, damage to which specific structures give the most severe defecit?
damage to the perirhinal and parahippocampal cortex of the temporal lobe
What is the major output of the hippocampus?
the fornix which projects largely to the mammillary bodies of the hypothalamus, output from which goes to the anterior thalamus. Furthermore, areas of the temporal cortex and amygdala make connections with the dorsomedial nucleus of the thalamus.
Rats given a microinjection of col-
chicine to destroy a specific population of cells (dentate granule cells) in their hippo-
campus at various time points and asked to complete the morris water maze tell us what about the hippocampus and spatial learning?
that the hippocampus is needed for consolidation of spatial learning, but that over successive weeks the site of the memory store is transferred elsewhere, probably the neocortex.
