Cognitive neuroscience 2 & 3: Studying brain function

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Lesion method

Investigating relationship between deficits in behaviour of brain-damaged patients and the site/extent of the damage 

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Visual agnosia

Bilateral damage to the visual cortex or temporal lobes results in impaired recognition of objects, patients can see the object but not identify it; problem connecting visual information with information stored about the nature of objects

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Balint's syndrome

Bilateral damage to parietal and occipital lobes results in difficulties locating and using objects, difficulty perceiving 2 objects at once, guiding eye movements, and reaching for objects, only affects movements that require visual control

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Single cell recording

Record activity from individual neurons, most often based on work done on animals

Microelectrode records activity from single cells

Each cell has a receptive field (area in space that cell responds to) and is tuned to a specific stimulus

Each visual area represents the field of vision and is topographic (brain area corresponds to visual field)

Multiple maps, hierarchically organized and interconnected

Higher-level maps: receptive field size of each cell is larger, cells respond to more complex stimuli

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CT scans

-          Computerised tomography

-          Invented in 1972

-          Uses x-rays to get detailed pictures of the brain

-          Different brain tissues have different densities and x-rays are transmitted through the brain

-          Not 2D, we can rotate and get a 3D model of the brain

-          Good for head injuries, strokes, tumours

-          Risk associated with exposure to radiation

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MRI

-          Magnetic resonance imagining

-          Developed in 1970s

-          Uses magnetic fields rather than x-ray

-          Avoids the risk of radiation

-          Not suitable for people with metal implants or certain tattoos

-          Can be uncomfortable for claustrophobic people

-          Gives a much more detailed, high resolution picture

-          Agent aligns protons in brain tissue, the alignment is disrupted via brief radio wave pulse, different tissues take different times to re-align depending on their densities

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EEG

-          Electrodes on scalp surface measure electrical activity generated by the brain

-          Direct measure of activity

-          Average over many trials to get a clear signal

-          We can quantify brainwaves (oscillations), and/or Event Related Potentials (ERPs), sudden changes in activity in response to stimulus

-          Excellent temporal resolution, real time measurement, relatively cheap

-          Poor spatial resolution, signals could be generated by multiple neural sources

-          Oscillations: brain waves that represent groups of neurons firing

-          Given an event, we look at whether and when spikes in activity occur

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MEG

-          Magnetic resonance imaging

-          Measure the magnetic field instead of electrical current

-          Picks up the magnetic fields that are produced by the brain

-          Can be measured in terms of oscillations, neurons firing on and off, event-related activity

-          Has the same advantages as EEG; good temporal solution, better source localisation, but not perfect

-          Very expensive

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PET

-          Measures blood flow

-          Injected with a tracer that follows the blood flow in the brain

-          Used by comparing two conditions; stimulated condition and control condition

-          Good localization, down to a resolution of 1 cm

-          Limited temporal resolution, only every 40 seconds

-          Exposure to radiation is a risk

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fMRI

-          Functional magnetic resonance imaging

-          Overlay one type of scan over another

-          The same scanner as MRI, but a different type of scan

-          Looks for blood rich in oxygen, which is directed to areas of the brain that are becoming active

-          Maps out where the oxygenated blood is in the brain

-          Good localisation precision

-          Temporal resolution is better than PET but not comparable with for example EEG

-          Some people are not suitable; any metal in their bodies, it’s also a loud scanner, and very expensive

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