Do Brain scans reveal mechanisms PDF

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Do Brain scans reveal mechanisms? ○ Not all plastcity is good ○ Neurogenesis can be looked at with fuorescent stains → show exercise increases # of cells - can induce more neurons in hippocampus ○ Need actve exercise to create new cell ○ Too many cells in hippocampus could lead to seizure actvity (could impair motor) ○ Neuroplastcity in a botle- some are not FDA approved ○ Serial lesion efect- if you damage a structure slowly over tme, you do not get same efect as if you take it out at once, which is done in surgery → lead to studying plastcity ■ Slow growing or fast ○People can functon well even if there is damage ○ Modern brain imaging studies do not ofer any greater explanaton of brain functoning than phrenology ○ Cannot explain recovery or sparing of functon afer injury ○ Associate brain structures with psychological and behavioral functons but associatons are NOT explanatons ○ Diference between phrenology and modern brain imaging is that

brain scans more accurately identfy brain structure that are actve when someone is doing something ○ Do not provide any informaton on mechanisms because they do not explain how those neural networks generate behaviors that are supposedly dependent on that structure ● Don’t need brain injury to see plastcity: environment and experience can alter cells even in adult brain ● Neurogenesis induced by exercise in the young and aged-related dentate gyrus ● Marketng of Brain Plastcity ○ Alpha focus has jumped to the top ranking in every category ○Specifcally designed to boost memory focus, reduce mental focus and support healthy brain functon ○ Alpha focus helps your brain naturally increase its potental and immediately improves functon ○Alpha focus jump-starts your mental focus ○ Natural ingredients smooth neural pathway to give razor-sharp focus without negatve side efects ● Plastcity and Repair of the Damaged Brain

○Why does a “rapid onset” of brain injury have diferent efects from the same injury that comes on more slowly… if it’s all about localizaton of functon? ○ Injury to the brain is a way to study plastcity ○ Injury-induced plastcity in the brain ■ In PET studies, during localizaton of sounds, blind humans actvate large parts of the visual cortex as well as larger regions of posterior parietal cortex-- areas involved in vision in seeing patents ■ Total lef brain removal in children ofen spares much language functon, suggestng a shif to the remaining intact hemisphere, but there may be subtle defcits later in life ■ PET and fMRI demonstrate that patents with lef hemisphere epilepsy have much greater language representaton in contralateral hemisphere compared to controls ■ Using PET, fMRI, and MEG, epileptc patents also show reorganizaton of language functons into healthy brain tssue surrounding the damaged area ■ How does other tssue “take over functon” while

maintaining its own functon? ○ Auditory compensaton for early blindness in cat cerebral cortex ■ Recorded single-cell actvity in the visual cortex of cats deprived of vision for several years afer birth and compared to normal controls ■ Auditory compensaton for early blindness in cat ■ Record single cell actvity in visual cortex (cat cerebral cortex) ■ Respond to tactle stmulaton and auditory input in a way that normal cat would not ■ Cells in auditory cortex move and take over in blindness ■ Plastcity, cortcal representaton in response to experience, visual cortex does not stop working, it just changes what the actual functon is ■ Other areas can take over ■ Normal cats responded to visual stmulaton ■ Deprived cats responded vigorously only to auditory or tactle stmulaton ■ Conclusion: cortcal representaton (functon) changed as a

result of experience from visual to auditory ○ Plastcity of the human motor cortex depends on injury context ■ Examined adults with lesions of the motor system (fast onset versus slow-growing lesions) using evoked motor potentals and rCBF ■ In acute patents, recovery is variable and correlates with rCBF changes in a number of non-motor areas ■ Slow (but same extent) lesions do not result in similar defcits and removal of the afected areas does not produce a motor defcit, indicatng marked reorganizaton of functon ○ Re-wiring the “connectome”? ■ Early visual deprivaton leads to a cross-modal expansion of brain regions in the auditory or somatosensory domain and a corresponding improvement of functon ■ This has been demonstrated in the superior colliculus and, most prominently, in cerebral cortex ■ Similarly- blindness from birth in humans can cause reassignment of cortcal regions from one modality to another, as functonal imaging studies have shown

■ Most excitng consequence of recent studies- sensory substtuton in the blind may become practcal reality, allowing blind individuals to harness the power of crossmodal plastcity to perceive, localize and recognize objects with their auditory and tactle senses ○ Recovery from subcortcal stroke: PET actvaton paterns in patents compared with healthy subjects ■ Single, focalized lesions lead to depression of metabolism in the area surrounding the injury, but also to functonal decrease in remote sites ■ Changes also in hemisphere contralateral to injury ■ In patents showing recovery of movement afer stroke, rCBF changes are seen bilaterally distributed whereas in normal actvaton is unilateral ■ Results demonstrate that the brain can show signifcant change in multple cortcal (and subcortcal) areas afer local cerebral injury even if injury is very restricted to pyramidal tract ○ Spontaneous Recovery and Disinhibiton ■ Other areas can “take over” for damaged tssue ■ Do previously “uninvolved” areas play a role in

compensaton? ■ How does area A take over for B and stll do A efectvelyespecially if the injury is bilateral? ○ Synesthesia in phantom limbs induced with mirrors ■ Phantom limb- lost an arm, but feel that forearm is stll atached, feel pain ■ Stmulate face → feel sensaton in fngers, but it is not there ■ How does brain reorganize? ■ changes/plastcity can change in minutes afer injury ■ Make latent connecton, but previously masked by dominant actvity- now unmask the latent connecton ■ Unclench good hand- pain in the amputated limb go away (example of plastcity) ■ Dynamic change ■ Cortcal somatosensory maps are dynamic ■ Cortcal maps can change or add new representaton ■ Compare brain plastcity to New York City (dynamic change in brain and New York) ■ A mirror refecton of the patent’s intact hand is superimposed on the felt positon of the phantom ■ When the normal hand is moved so that the phantom is perceived to move in the mirror, kinesthetc sensatons emerge in phantom ■ Sensaton of “clenching” spasms could also be removed

when the mirror was used to facilitate “opening” of the phantom hand ■ Data “suggest that there is a considerable amount of latent plastcity even in the adult human brain. … hierarchal model of the brain… needs to be replaced with a more dynamic, interactve model.” ○ Pros and Cons of Mapping Functons in the Brain ■ Intracarotd amytal testng doesn’t afect all parts of the hemisphere in the same ways ■ Inactvaton may only be partal- causing variable outcomes ■ PET and fMRI measure blood fow, not functon or brain actvity directly ■ Tells us what areas partcipate but not which are critcal ■ Astrocyte actvity mediates cerebral blood fow directly by afectng vasodilaton in response to neural actvity ■ Magnetoencephalography (MEG) is good, but subject to environmental noise ■ Most work emphasizes fronto-cortcal actvites-- overlooking subcortcal and other changes contributng to compensaton ○ Rapid reorganizaton and re-mapping the brain - I ■ Reorganizaton in response to injury can occur within minutes afer the damage ■ Can loss of input into one cortcal area lead to map expansion or to capture of that area by another modality? ■ Is this change adaptve or an example of “negatve plastcity”?

○ Time sequence afer median nerve injury ■ Inital changes are unmasking ■ Later changes imply sproutng and/or reorganizaton ■ Level of map detail increases over tme ○ Rapid reorganizaton and re-mapping the brain -II ■ Rapid reorganizaton occurs in motor and sensory systems ■ Training and rehabilitaton (therapy) may be needed to produce sustained reorganizaton ■ Inappropriate or ill-tmed training can increase extent of injury and prevent recovery ■ Individual diferences in cerebral organizaton are important and individual history plays a role ○ Phantom Limb Reorganizaton → mirror-box illusion (immediate reorganizaton of functon) ○ Conclusions ■ Cortcal somatosensory maps are dynamic ■ Cortcal maps can change (or add new) representatonal matrices ■ Self-organizing capacity of sensory feld does not end early in life ■ 2 mapped representatons can simultaneously occupy the same sector of cortex ○ Morphological Plastcity- regeneraton and neurogenesis in the adult brain?...