Methods for studying the living brain

Question 1

Broca’s aphasia

Answer 1

A disorder of speech production, patients are still able to comprehend speech though

left hemisphere, posterior part of the inferior frontal gyrus

Question 2

Apraxia of speech

Answer 2

speech is slow, laborious and non fluent

Question 3

Agrammatism

Answer 3

loss of grammatical function words e.g. a, the, some, about but not content words e.g. boy, smart, university

Question 4

Anomia

Answer 4

difficulty finding the appropriate word

Question 5

Wernicke’s aphasia

Answer 5

a disorder of language comprehension

left hemisphere, posterior part of the superior temporal gyrus

Question 6

Wernicke’s aphasia characteristics

Answer 6

• speech is fluent and unlaboured
• rise and fall of intonation is completely normal
• don’t realise that they have a speech deficit
• patient will use grammatical function words but may use few content words and often will insert nonsense of jargon

Question 7

Limitations of clinical neuropsychology

Answer 7

• Patients are often difficult to test intensively
• Problem of replicability in single cases
• Assumes local lesions have local effects
• No control of lesion size or location in the brain- ‘experiments of nature’

Question 8

Ablation studies in animals

Answer 8

the process of making small lesions in distinct parts of the brain of animals and to observe the effects of these lesions on behaviour

Question 9

Delayed non-matching to sample

Answer 9

• the initial card shown to the monkey does not have the food reward
• normal monkey quickly learns that the reward is hidden under the card that was not rewarded in the initial trial
• if the monkey’s memory is impaired (ablation of the medial temporal lobes) it will select random cards. The longer the delay between learning the correct response and having to make a choice the more error
• therefore damaging the hippocampus impairs memory and learning

Question 10

Limitations of ablation methods

Answer 10

1. the experimental lesion may still effect distant brain structures
2. there are many aspects of cognition that are difficult or impossible to test in other species e.g. language and complex reasoning

Question 11

Extracellular microelectrode recording

Answer 11

recording the electrical activity (action potentials) from single neurons using a fine microelectrode located in the extracellular space.

Limitation: it is not possible to guarantee that the electrical signal being recorded is from one neuron, it could in fact come from several

To overcome this limitation intracellular recording is used where the microelectrode is placed inside the cell body of a neuron, this process is extremely technical

Question 12

Neurons receptive field (the visual cortex)

Answer 12

single neurons respond to different visual properties, shape, colour, movement etc.

• most neurons in the visual cortex only respond to stimuli that appear in a limited region of space (the neurons receptive field)
• receptive fields of neurons in the primary visual cortex tend to be quite small whereas the receptive fields in higher association areas, quite large
• in the primary visual cortex, adjacent neurons tend to have overlapping receptive fields
• damage of the visual cortex can lead to blindness for the corresponding location of the visual field

Question 13

Structural brain imaging techniques

Answer 13

provide a static snapshot of the anatomy of the brain

Question 14

Functional brain imaging techniques

Answer 14

reveal which areas of the brain are metabolically active, either at rest or while a person is performing a particular cognitive task

Question 15

Computerised tomographic (CT) scanning

Answer 15

allows us to see what is occurring in the brain structurally e.g brain shrinkage due to Alzheimer’s disease, region of damage caused by a stroke

Question 16

X-ray detection in CT scanning

Answer 16

1. X-ray beams are passed through the head
2. a radiation detector opposite the beam picks up the amount of X-ray energy that emerges from the other side of the head
3. computer reconstructs images

-tissues of different density absorb different amounts of x-ray energy
e.g. bone absorbs a large amount of x-ray energy = radio opaque
cerebrospinal fluid absorbs little x-ray energy because it is a liquid

On a typical CT scan, bone = white, CSF = black grey and white matter of the brain = different shades of grey

limitation: does not differentiate well between grey and white matter
poor spatial resolution (ability to discriminate fine structures)

Question 17

Magnetic resonance imaging

Answer 17

• MRI exploits the magnetic properties of brain tissue (hydrogen)
• Enormous superconducting magnet inside the scanner that is cooled by liquid helium
• MRI is sensitive to the behaviour of protons in the nuclei of hydrogen atoms
• Hydrogen atom consists of nucleus with one proton and a single orbiting electron
• protons in the nucleus have a characteristic motion ‘spin’ creating a tiny magnetic field
• when the body is placed in the MRI protons align in a direction that is parallel with the magnetic field
• radio frequency pulse is passed through the head which perturbs the axis of spin of the protons. After pulse protons realign into the orientation of the static magnetic field
• synchronised relaxation (realignment) of protons produces energy that is picked up by detectors surrounding the head
  computer reconstructs a 3D image, which reflects the distribution of protons and other magnetic agents in tissue

Question 18

Characteristics of MRI

Answer 18

provides images with high spatial resolution
it can discriminate structures down to 1mm
excellent differentiation between grey and white matter (because the density of protons is much greater in grey matter

Question 19

Scalp- recorded EEG

Answer 19

measures the weak electrical signals produced by the brain

1. electrodes are placed at one or more points on the surface of the scalp
2. the electrical signals detected by the electrodes are sent to an amplifier and are displayed on a computer monitor or printed onto paper
3. the waveforms indicate the strength and rhythmicity of electrical activity in the brain

EEG has good temporal resolution (can discriminate very brief events in time), but poor spatial resolution.

Question 20

Scalp- recorded event-related potentials (ERP)

Answer 20

• same EEG equipment
• measuring an event or interest e.g. the brains ability to process a brief sound
• can’t deduce anything from a single recording
• many trials averaged reveal the response to the signal

very good temporal resolution, but poor spatial resolution

Question 21

Functional magnetic resonance imaging (fMRI)

Answer 21

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Question 22

Transcranial magnetic stimulation (TMS)

Answer 22

1. A TMS coil carrying an electrical current is held over the scalp
2. focal magnetic pulse is generated activating a small region of the cortex (10-15mm)
3. the activation acts like a ‘virtual legion’ temporarily disrupting the tissue for a few hundred milliseconds
4. if a particular brain region is critically involved in a task, then TMS of that region should affect performance