When things go wrong - Reach Cambridge · 2019. 11. 29. · Lesson 2 (REACH Psychology, week 3) In...
Transcript of When things go wrong - Reach Cambridge · 2019. 11. 29. · Lesson 2 (REACH Psychology, week 3) In...
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When things go wrong
Lesson 2 (REACH Psychology, week 3)
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In this lesson ● Why study lesioned brains?● Types of lesions ● Famous case studies● TMS
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First - medical scans Measure the level of oxygenation in different types of tissues
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Brain lobes
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Medical scans T2 for spotting lesions in the WM T1 for atrophy
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Which brain is more functional?
Child after near drowning
Child after epilepsy
Adult stroke
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Why study lesioned brains? ● Instrumental in treatment and early diagnosis ● Reverse engineering functional specialisation of brain
areas (a) From real lesions (b) From TMS (transcranial magnetic stimulation)(c) From invasive animal models ● (examples to follow)
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Types of lesions Neurosurgery: cortical tissue is surgically removed to reduce symptoms of epilepsy
This group of patients had problems with autobiographical memory after resection
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Types of lesions Neurosurgery: split brain
Corpus callosum is cut to stop seizure
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Types of lesions Strokes - disruptions of the blood supply to the brain, resulting in local or global death of neurons
2 types:
Blood vessel ruptures - brain haemorrhage, 13 % of strokes are haemorrhagic.
Blood vessel is blocked - embolism (non-local) or thrombosis (local); occurs as a result of an obstruction within a blood vessel supplying blood to the brain. It accounts for 87 % of all stroke cases.
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Blood Clot
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Types of lesions Embolism or thrombosis
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Types of lesions brain haemorrhage
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Tumor ● abnormal growth● creates pressure and
abnormal circulation in the areas surrounding the tumor
● May lead to atrophy of the surrounding tissue
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Neurodegenerative disorders Happens with age
Most common: dementia and Alzheimer's
Dementia - an umbrella term to characterise diseases that cause the loss of the nerve cells in the brain
Alzheimer's - most common type of dementia
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Neurodegenerative disorders
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Alzheimer's disease
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Famous brain lesions (and what they taught us)
Broca’s brain
● ‘Precise’ areas of stroke ● A specific set of symptoms ● Broca’s area to this day is strongly related to speech processing,
specifically production
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Famous brain lesions Not so simple
● In 2007, a team at the University of California, reexamined Broca’s brain
● Leasion turned out to be more extensive
● Multiple areas contributed to the severity of the disorder
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Language-related pathways
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Me and Broca in Paris
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Famous brain lesionsPhineas Gage
● A terrible injury to his brain● Gage did not die or even pass
out● However his social behaviour was
completely altered
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Famous brain lesionsA man frozen in time
● Removal of Both Medial Temporal Lobes (Loss of hippocampus, amygdala, and perirhinal cortex)
● developed severe anterograde amnesia● intelligence was not affected
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Comparisons
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What might these lesions mean for behaviour? (10 min)
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Conclusions Lesion studies are critical for identifying functions of different brain areas
Important for early diagnosis
And recovery
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What are the caveats of lesion studies?
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caveats of lesion studiesModern imaging techniques are not precise in lesion location identification (but 7 Tesla!)
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What are the caveats of lesion studies?● Based on individuals (each brain is unique)● Lesions often force re-organisation ● Danger of one-to-one mapping between the area and a
function
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Transcranial Magnetic Stimulation ● A way to temporarily ‘lesion’ a brain area ● The effects are small and do not last● Early experiments were very crude ● First stimulation of the peripheral nerves and the human
motor cortex (Barker, 1985)
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TMS - how it works ● Faraday’s law - a time-varying
magnetic field induces an electric current in conducting material (measurable voltage)
● This field changes the polarisation of the neurons
● Repolarization = action potential
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TMS A number of designs of the coil exist - the most common is the figure-8 coil.
The point of the greatest fluctuation of the magnetic field is the intersection of the two loops.
Making this point (patch) most likely to evoke an activation
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Tms- experiment● Every experiment has a control condition● What would be a TMS control?● How can we evaluate if it worked?
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Next lesson Methods!
How do we measure brain activity?