when things go wrong - reach cambridge · 2019. 11. 29. · lesson 2 (reach psychology, week 3) in...

When things go wrong

Lesson 2 (REACH Psychology, week 3)

In this lesson ● Why study lesioned brains?● Types of lesions ● Famous case studies● TMS

First - medical scans Measure the level of oxygenation in different types of tissues

Brain lobes

Medical scans T2 for spotting lesions in the WM T1 for atrophy

Which brain is more functional?

Child after near drowning

Child after epilepsy

Adult stroke

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)

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

Types of lesions Neurosurgery: split brain

Corpus callosum is cut to stop seizure

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.

Blood Clot

Types of lesions Embolism or thrombosis

Types of lesions brain haemorrhage

Tumor ● abnormal growth● creates pressure and

abnormal circulation in the areas surrounding the tumor

● May lead to atrophy of the surrounding tissue

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

Neurodegenerative disorders

Alzheimer's disease

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

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

Language-related pathways

Famous brain lesions (example)

Me and Broca in Paris

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

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

Famous brain lesions (example)

Comparisons

What might these lesions mean for behaviour? (10 min)

Conclusions Lesion studies are critical for identifying functions of different brain areas

Important for early diagnosis

And recovery

What are the caveats of lesion studies?

caveats of lesion studiesModern imaging techniques are not precise in lesion location identification (but 7 Tesla!)

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

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)

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

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

Tms- experiment● Every experiment has a control condition● What would be a TMS control?● How can we evaluate if it worked?

Next lesson Methods!

How do we measure brain activity?