Hemispheric Specialization + Memory I &II
Hemispheric Specialization + Memory I &II PSYCH UA-25
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This 5 page Class Notes was uploaded by Brianna René on Tuesday April 5, 2016. The Class Notes belongs to PSYCH UA-25 at New York University taught by Clay Curtis in Winter 2016. Since its upload, it has received 138 views. For similar materials see Cognitive Neuroscience in Psychlogy at New York University.
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Date Created: 04/05/16
2.0.2. Hemispheric Specialization Cerebral Specialization: Adaptation of part of the brain to a particular function. Similar to specialization of function only it’s with the two hemispheres of the brain. There is functional asymmetry or lateralization of function between hemispheres. Structural Asymmetries: An exaggerated computer reconstruction shows a right frontal lobe protrusion, and a left occipital protrusion. Enlargement of the left planum temporale (embedded in sylvian fissure) may have a link with language processing Differences in cell size in language processing regions (left hemisphere) Connecting the Hemispheres: Commissures are white matter tracts that connect the Brain’s hemispheres. The largest commissure is Corpus Callosum Association Tracts integrate information within the same hemisphere Projection Tracts integrate information between deeper nuclei & the surface. Callosal Relay Model : Explains perceptual asymmetries by suggesting that the transfer of information to the specialized hemisphere degrades that information and increases the time to respond. Double Filtering by Frequency Theory: All sensory information is initially processed in both hemispheres but they filter the information differently afterwards. Studying Hemisphere Specialization -Studies with neuropsychological patients -Unilateral lesion patients Wada Test: Injected anesthetic into left carotid artery so it goes to the left hemisphere and “puts it to sleep.” This test was used to determine if the left hemisphere was most responsible for speech. A Corpus Colostomy is the severing of the corpus callosum, and is done in patients who have severe epilepsy. Studies of these patients can show how the two hemispheres operate in isolation. Limitations to using Split-Brain patients Patients may have abnormal functioning in their brains because they are epileptic. In some patients, not all transcortical connections may be severed completely. Depending on the amount of the Corpus Callosum left intact, there may be little to no communication between the two hemispheres. So two patients with different degrees of severance to their CC may yield different behavioral results. Patients cannot name things that appear in the left visual field, but they can draw it since the info goes to the right brain. We can study Hemispheric Specialization in healthy patients as well behavioral studies neuroimaging studies The left hemisphere is dominant for speech in ~95% Right Handed people ~60% Left Handed people However, the idea that each hemisphere is lateralized ONLY for certain tasks isn't true. The right hemisphere does have some capability of language processing to a small extent.(some understanding of language, but unable to make inferences) Right ear advantage in dichotic listening tasks. Does the right ear have better access to language processes or is it just better at hearing or identifying information? (double dissociation necessary to prove this) Right Hemisphere: emotional prosody. Non-linguistic, but emotional part of speech. The connotative parts of speech Lateralization of Visuospatial Skills In split brain patients, depending on the hand used to do the task, the patient’s performance at the task vines. Right hemisphere was proven to be more important in spatial processing, and it may also be better at face processing Global vs. Local Processing: Information is stored at multiple scales Unilateral lesion patients (with damage in respective hemispheres) With damage in the left hemisphere, it is slower in identifying local targets (details) With damage in the right hemisphere, it is slower in identifying global targets (big picture). Both hemispheres are capable of processing both global and local information, but one is more efficient than the other. Problem Solving & Lateralization Matching Strategy: When picking between answers, humans alternate their choice and pick the correct answer 75% of the time when asked. There’s still a chance for that to be wrong, so actually they are right 50% of the time. (uses left hemisphere). Maximizing Strategy: When picking between answers, rabbits pick the correct answer every time, so that they are right 75% of the time in reality, thus maximizing their results. (This method is much better and employs right hemisphere). In split brain patients, left hemisphere predicts upper quadrant 80% of the time in matching strategy. Right hemi predicts upper quadrant almost 100% of the time in maximizing Left Hemisphere: “The Interpreter” It tries to rationalize. Tries to find order in chaos Searches for causal relationships and makes causal inferences Interprets events. Right Hemisphere Approaches problems simply Makes causal/relational perceptions Doesn't engage in interpretation The exaggeration of Hemisphere specialization in popular culture leads to a naive view of the brain. Each does not represent information in an identical manner, and each is better at representing and processing different types of information. 2.0.3. Memory I & II Memory is unified around a single biochemical mechanism, not a single part in the brain. There isn't just one place where memory is stored because each modality in the brain has its own memory system. Memory is a distributed property of the mammalian brain. Stages of Memory Encoding: Processing incoming information Amnesic patients w/ hippocampal damage were insensitive to relational changes in scenes Prefrontal Cortex & Encoding: Lesions here do not result in global amnesia (total amnesia) but there is some evidence for episodic memory deficits (trouble searching for information) subsequent memory effects material-specific effects in PFC Consolidation: Creating a durable memory trace over time An episode or memory is represented by activation in neurons. The hippocampus binds features of the episode/memory & over time, the information becomes bound together in the cortex. Eventually memories are stored and consolidated and no longer rely on the hippocampus for their retrieval. Evidence for consolidation: There is a pattern of temporally-graded (time gradient) anterograde amnesia. People with bilateral hippocampal damage do not have trouble recalling old memories (they have been consolidated over time) but they have trouble with more recent memories. In healthy brains, there is less Medial Temporal Lobe activity for more remote memories. When they reach the stage of total consolidation, memory retrieval no longer depends on MTL. Storage: Maintaining a permanent record Anterior and Lateral Temporal Lobe lesions can produce Retrograde amnesia w/o Anterograde amnesia These regions may be involved in retrieval of info from long term memory stores, not the storage system itself. Memories may be stored as distributed representations throughout the cortex Retrieval: Accessing the stored information The hippocampus retrieves new things Hippocampal activation during encoding can predict which items will be retrieved. So items that provoked more hippocampal activity have a higher chance of being retrieved. Episodic Retrieval: After you perceive something for the first time, the same neurons involved in that activity are reactivated upon retrieving that thing from memory. Context Dependent Memory: Improved recall of specific events or information when the context they were encoded in are the same. Mechanisms of Memory Hebbian Learning: “Neurons that fire together, wire together.” Persistent activity causes a long lasting change in one or both neurons (pre and post- synaptic) either in dendrite structure or intracellular machinery (synapses) Long Term Potentiation (LTP): Stimulating pre-synaptic neurons increases amplitude of EPSPs (Excitatory potentials) in post-synaptic neuron. Early LTP: Increases NT sensitivity in post-synaptic receptors and increases NT release from pre-synaptic cells. Late LTP: Protein synthesis and structural changes result in the formation of new synapses. this may be the substrate of long term memory. This allows for plasticity in the brain and it also has a long term effect. Non-Declarative Memory Procedural Memory: Basal Ganglia Perceptual motor skill learning is impaired in parkinson's & huntington's diseases Repetition Priming Tasks: Amnesics are able to perform priming tasks (implicit tasks). They are bad however at explicit tasks such as free recall and recognition. Repetition Suppression: Repeated items show less activity in the brain (prefrontal and visual areas) Priming vs. Episodic Memory Patient M.S: had a right visual cortex lesion. He did not show benefit from being shown repeated words/ objects. His episodic memory was intact, but he had an impairment with priming. Classical Conditioning “Delay Conditioning”. Air puff/eye blink response. EVery time a tone sounded, participants would receive a puff of air in their face at the same time that would cause them to blink. Human amnesic patients still have DC in tact. It is thought to depend on plasticity in the cerebellum. “Trace Conditioning.” A delay is placed between the tone and the air puff. Rabbits w/ lesions and human amnesics show diminished trace conditioning.