Hemispheric Assymetry

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Gina Grimshaws lectures and readings on hemispheric assymetry

Are we right or left-brained?

Neither - coordinated efforts of both hemispheres is needed

How do we investigate the brain?

Brain damaged patients (unilateral, split-brain), neuroimaging, perceptual assymetries

Broca

first to tie function with anatomy, leading to assumption that left was the most important and intelligent side of the brain

Contralateral organisation

Damage to the left side of the brain leads to problems with the right side of the body

Aphasia

language disturbances

Dyslexia

Reading problems

Apraxia

Motor problems

Associative Agnosia

Difficulty recognising objects

Left hemisphere damage leads to

Aphasia, Dyslexia, Apraxia, Associative Agnosia, Depression

Broca, 1860

Localised language to left frontal lobes

What is a stroke?

heart attack in the brain - blocked blood vessels - causing holes in the brain

Jackson, 1878

Localised spatial awareness to the right hemisphere - also that it had a role in language

Right hemisphere damage leads to

Aprosodia, loss of meaning, Amusia, loss of spatial awareness, Hemispatial neglect, prosopagnosia, euphoria, anosognosia

Aprosodia

No emotional tone in voice

Amusia

Loss of music

Hemispatial neglect

Attentional problems

Prosopagnosia

Difficulty recognising faces

Anosognosia

Lack of awareness of deficits

How do the hemispheres work together?

Speech perception, vision, emotion

Speech perception

LH - words and syntax, RH - expression, tone, meaning

Vision

LH - details, RH - big picture

Emotion

LH - positive emotions (approach), RH - negative emotions (avoid)

Electrical Stimulations - when, on what

Penfield 1930s, during surgery to map language areas

Wada test - what

Inject sodium amytal (amobarbital) into middle cerebral artery on left or right side

What joins the two side of the brain?

Corpus callosum, 2 million axons connect L and R cortex

How do patients have split brains? - why

Callosum cut (to control epileptic seizures), but subcortically still intact

How do split brain patients behave?

Normal, but competition between hands

What is learnt from split-brain patients?

LH - speech production, RH - language abilities (reading of concrete words, auditory, skips to meanings), visual-spatial abilities

Perceptual Assymetries

LVF projects to RH and viceversa, Left ear projects to RH and vice versa

Structural imaging - 2, meaning

CT, MRI, Can reveal structures but not involvement in behaviours

Functional imaging

fMRI, EEG/ERP, PET, TMS

CT

computerised tomography, X-rays taken at different angles to construct brain picture

MRI

Magnetic Resonance Imaging, passing magnetic field through brain and detecting reverberations

fMRI

Functional Magnetic Resistance Imaging, detect changing aspects of brain physiology without radiation, gives 3D image or brain at work showing active parts

EEG/ERP

Electroencephalography, detects electrical currents from neurons, by affixing electrods to the head, indiates activity at brain's surface

PET

Positron emission tomography, 3D localisation of brain function, injecting with radioactive sugar absorbed by brain cells according to level or activity

TMS

Transccranial magnetic stimulation, series of magnetic pulses at a location causing disturbances directly underneath it, temporary lesion

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