Brain and Behavior Chapter 11
Brain and Behavior Chapter 11 Nsci3300
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Date Created: 11/22/15
Chapter 11: Learning and memory and Amnesia 11/19/2015 ▯ Learning- how experience changes the brain ▯ Memory- how changes are stored and subsequently ▯ HM o Had medial portion of temporal lobe removed (both sides) Including most of hippocampus, and amygdala o Memory for events predating surgery (retrograde) remained largely intact his short term memory (digit span) was intact however he had lost the ability to form new long term memories (anterograde) As soon as he stopped thinking about a new experience it was lost forever o Tests showed that HMs brain was capable of storing Long term memories but he had no conscious awareness of them o Tests used for HM Digit-span test +1 Could not get more than 8; most people can get about 15 Block tapping Proved HM has global amnesia (info present in all modalities) Mirror drawing test Proved memories were stored (score increased) but HM could not recalled having done the task before Incomplete-pictures test Proved motor task was no exception long term memory was stored for other tasks unconsciously as well Pavlovian conditioning Was conditioned (effects lasting 2years) but couldn’t recall training o 3 major contributions Showed important roles of medial temporal lobe in memory Spawned massive research efforts aimed at clarifying mnemonic role of hippocampus Supported theory that there are different modes of storage for short term, long term, and remote memory Led to creation of two distinct categories of long term memories Explicit Implicit Medial temporal lobe amnesia o Not unique to HM o Symptom: inability to form explicit long term memory but ability to from implicit long term memory remains in tact o Test that assess implicit memory=repetition priming test o What is the advantage of having a second, conscious system? Flexible use of information o Explicit long term memory Semantic Facts and info Episodic Events of ones life *Ppl with medial temporal lobe amnesia have particular difficulty with this Difficult to spot episodic memory problems Effects of Global Cerebral Ischemia on the hippocampus and memory o (An interruption of blood supply to entire brain) o Selective hippocampal damage can acause medial temporal lobe amnesia Transient global amnesia (sudden onset in otherwise normal adult) Severe anterograde amnesia and moderate retrograde for explicit episodic memory Lasts only 4-6 hrs Linked to abnormalities to CA1 of hippocampus Amnesia of Korsakoff’s syndrome o Disorder of memory associated with consumption of large amounts of alcohol o Amnesia is similar to medial temporal lobe amnesia (anterograde amnesia for explicit memory= early symptom) but the disorder progresses (retrograde amnesia develops) deficits in explicit > implicit o Diffuse damage= not easy to identify cause of amnesia o It is unlikely that memory deficit of Korsakoff’s patient are attributable to damage of any single structure Amnesia of Alzheimer’s disease o Major cause of amnesia o More general memory deficits o Major anterograde and retrograde deficits in explicit memory also deficits in short term and implicit (verbal and perceptual) o Acetylcholine depletion= factor but not only cause of amnesia Amnesia after concussion: evidence for consolidation o # 1 cause of amnesia- called posttraumatic amnesia (PTA) o Permanent anterograde for moment following confusion and permanent retrograde for moment/event leading up to blow o Gradients of retrograde amnesia seem to prove memory consolidation Only lose recent memories because older ones have been strengthened o Lasting memories become more resistant to disruption throughout a persons life. Each time a memory is activated it is updated and linked to other memories. Increases resistance to disruption o Engram: a change in the brain that stores a memory o Reconsolidation hypothesis: each time a memory is retrieved from long term it is temporarily held in liable (changeable) short term where it is susceptible to PTA until it is reconsolidated Evolving perspectives of the role of hippocampus in memory o 1970s animal model of HMs disorder o Role of hippocampus in object-recognition memories in minor o Compared to the contribution of adjacent medial temporal cortex o Today, hippocampus is considered to be one of several brain structures that play an important role in memory Neurons of the medial temporal lobes and memory o Morris water maze test- swim to platform hidden below surface Hippocampal damage= harder to learn o Radial arm maze test- win-stay- reference and working memory targeted Hippocampal damage=deficits in both reference and working memory o Many hippocampal neurons—place cells (neurons that respond only when a subject is in specific locations Consistent with view that hippocampus plays role in spatial processing o One line of research focused on entorhinal cortex o Grid cells- how hippocampal place cells obtain their spatial info o Jennifer aniston neurons Highly selective, invariant responses In hippocampus even more selective and invariant Respond to ideas/ concepts rather than particles— known as concept cells If concept cells respond to more than one concept the concepts are someone related Where are memories stored? o Memories are stored diffusely and thus survive destruction of any single structure o Memory become more resistant to disruption over time o Areas of brain that are active during retention tend to be same as active during experience Partial attention to inferotemporal cortex=important role is storing visual memories o Amygdala involved in strengthening emotionally significant memories stored in other structures o Prefrontal cortex- deficit in temporal order and working memory o Sensorimotor memories= cerebellum and striatum May play a role in certain types of memories with no obvious motor components o Cerebellum=storage of memories of learned sensorimotor skills o Striatum- store memories for consistent relationships between stimulus and response Synaptic mechanisms of learning and memory o Hebbs hypothesis=enduring facilitation of synaptic transmission are then neural bases of learning and memory o Long-term potentiation: the facilitation of synaptic transmission following high-frequency electrical stimulation applied to presynaptic neurons Most frequently studied in rap hippocampus o LTP 2 key properties that Hebb proposed as characteristics of physiological mechanisms of learning and memory Last for a long time after multiple stimulation Develops only if firing of presynaptic and postsynaptic Co-occurrence o LTP can be elicited by low levels of stimulation that mimic neural activity Most prominent in structures linked to learning and memory (hippocampus) Conditioning can produce LTP- like changes in hippo Drugs that influence memory influence LTP The induction of maximal LTP blocks the learning of a Morris water maze until the LTP has subsided Mutant mice that display little hippocampal LTP have difficulty learning the Morris water maze; LTP occurs at specific synapses that have been shown to participate in learning and memory in simple invertebrate nervous system o Induction of LTP learning NMDA- prominent at synapse where LTP is studied NMDA receptor does not respond unless Glutamate binds At the same time as Postsynaptic neuron is depolarized When occur simultaneously there is an influx of calcium IONs that trigger action potential and the cascade of event that induce LTP o Maintenance and Expression of LTP Expression/ maintenance involves changes in both pre and post synaptic neurons Dendritic spines keep calcium ion from passing around and thus they exert their efforts locally Discovered LTP causes structural changes Transcription factor were discovered as a way neurons activity could change its structure Signal passing between post and pre synaptic neurons= nitric oxide o Variability of LTP NMDA receptor-mediated LTP involves a complex array of changes that are difficult to sort out LTP has been documented in other parts of the CNS where it is mediated differently o Biopsychology memory and you Infantile amnesia: remember virtually nothing of event of our infancy Implicit memories of early years Nootropics (smart drugs) thought to improve memory – not conclusive ▯ ▯
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