Effects of brain damage and brain stimulation as a way of studying the brain

Question 1

Problem of causality

Answer 1

1. brain imaging makes it possible to examine the brain substrates of psychological processes - teaches which parts of the brain are linked
2. however neuroimaging techniques suffer from one serious limitation - the fact that some brain activity is associated with a task/process does not mean the activity causes the observed behaviour or hypothesised psychological process
3. but does it clear there’s some association

Question 2

non essential activations

Answer 2

1. some brain regions may be involved in the learning of any new task, but may not be required when it is learnt
2. some brain areas are recruited as a back up in case processing requires extra resources or effort
3. some process A essential for the task may often co-occur with another process B that is not essential for the task

Question 3

determining causality

Answer 3

1. the only definitive solution is to examine whether behaviour/performance is affected when the brain activity is disrupted in a particular area
2. in animals, lesions can be produced experimentally
3. in humans, we can examine the effect of neurosurgery, stroke, brain trauma or tumours, neurodegeneration, infection of brain tissues

Question 4

what is neuropsychology

Answer 4

1. neuropsychology is the area of psychology that examines the effects of brain damage on abilities and behaviour
2. if damage to a particular brain region/structure is systematically associated with a certain cognitive impairment, that region/structure is necessary for that cognitive process to function
3. therefore that brain region must be part of the substrate for that cognitive process
4. neuropsychology is thought to have emerged in the 19th century, Broca

Question 5

Clinical neuropsychology

Answer 5

1. applied clinical variant
2. experts on the behavioural and emotional consequences of brain damage
3. clinical neuropsychologists assess the effect of brain damage in patients, diagnose neural disorders and help adjust

Question 6

Language

Answer 6

1. Broca’s and Wernicke’s area in motor cortex
2. Broca’s areas - studied brains of patients who had impaired speech, one patient couldn’t say anything other than tan, found in post mortem a lesion in the left inferior frontal lobe
3. Wernicke’s aphasia - ability to comprehend the meaning of words is highly impaired, reading and writing impaired, often use sentences but with the wrong words or non existent words

Question 7

corpus callosum

Answer 7

1. connects hemispheres
2. Sperry and Gazzaniga - studied patients who underwent callosotomy to limit the spread of epileptic activity
3. they tested visual fields, visual stimulus of horse in left field, when asked what goes on it they say i don’t know but can draw saddle with left hand
4. reversible numbing of left hemisphere, given an object to left side, when asked what they were given they can’t answer but can pick object out
5. shows language is heavily biased to the left hemisphere

Question 8

memory

Answer 8

1. temporal lobe amnesia case study HM - severe epilepsy, bilateral, medial temporal lobe resection, epilepsy was improved but showed a nearly total profound amnesia (both partial retrograde and profound anterograde), working memory and procedural memory were somewhat normal
2. Clive wearing - hippocampus link to memory

Question 9

attention

Answer 9

1. hemispatial neglect - inattention to parts of the visual field, affects up to 2/3 of right hemisphere stroke patients
2. neglect symptoms - only attend to things on the right, move in opposite direction from you if you come from neglected side, problems reading and navigating space
3. unclear what happens in neglect - lateralisation to the left side of the field suggest to some to indicate that attention is inherently biased to the right and that some function bringing it left it impaired, another possibility is an issue with the internal representation of space in the brain or that the initiation of the motor system in certain directions is impaired

Question 10

neuroimaging - key approaches

Answer 10

1. may want to run imaging experiments to see where a certain task/function is localised
2. may be interested in whether a certain task/condition has a qualitatively different pattern of activation from another condition
3. some argue this approach is more useful because it can tell us whether the two experimental conditions rely on the same procecss
4. this approach relies in part on the logic of dissociations

Question 11

logic of dissociations

Answer 11

1. meuropsychological data can be used to test theories about the architecture of psychological processes even without knowing the exact location of the damage
2. one key question when investigating processes in recognition and writing of letters is whether the recognition and writing of vowels rely on different psychological process from consonants
3. this dissociation may indicate that the two classes of letters are processed differently
4. Cubelli found that one of his patients could write consonants but left gaps where there were vowels, the other made spelling errors mostly on vowels

Question 12

single dissociation

Answer 12

1. Cubelli’s patients are an example of a single dissociation, which is not sufficient for drawing the conclusion that there is a qualitative difference between how the mind represents vowels and consonants

Question 13

double dissociation

Answer 13

1.Kay and Hanley identified a patient who made more spelling errors in consonants than vowels but still both
2. one type of item gets more resilient to the effects of damage

Question 14

neuropsychology strengths and limitations

Answer 14

1. enables causal inference
2. main drawback is that lesions resulting from trauma are rarely anatomically selective, they tend to affect multiple brain regions/structures
3. brain damage is always associated with general cognitive, emotional and personality changes whose effect on cognitive performance is very considerable and difficult to separate from the effects of damage to a specific region

Question 15

transcranial magnetic stimulation

Answer 15

1. a non-invasive magnetic stimulation of human motor cortex
2. neurophysiology - a large current is briefly discharged into a coil of wire held on thesubject’s head, the current generates a rapidly increasing magnetic field around the coil of wire which passes into the brain, in the cortex the magnetic field generates electric current through the neurons’ membranes
3. TMS over the primary motor cortex induces muscle contractions
4. TMS over the primary and secondary visual cortex results in the perception of flashing patterns “phosphenes” where the shape and size depends on site, strength, duration and timing of stimulation

Question 16

effects of TMS on performance

Answer 16

1. a TMS pulse typically induces a brief chaotic increase in neural activity followed by a more sustained reduction in excitability
2. this results in a disorganisation of neural activity, typically resulting in impaired performance
3. thus the effect is similar to that of a neurological lesion, only mild, reversible and safe

Question 17

TMS spatial resolution

Answer 17

1. typically 10-20 mm, 5-10 at best
2. influenced by distance from the scalp and connectivity between target region and adjacent regions

Question 18

TMS temporal resolution

Answer 18

1. subjects presented with sets of three letters and asked to report the letters on each trial
2. on each trial, TMS applied over the visual cortex at a slightly different time
3. specific times affect performance, others do not
4. TMS clearly capable of telling when the targeted area was involved in processing
5. the effects of a single TMS pulse on behaviour are rather breif so temporal resolution is high

Question 19

what can we infer from the effect of TMS

Answer 19

1. functional-anatomical inference - if cortical area x is essential for performing a given task
2. chronometric inference: at what time does stimulation affect performance relying on a hypothetical psychological process

Question 20

suitable control condition

Answer 20

1. need to control for somatosensory and auditory effects of TMS
2. TMS is not enough as a control because at least some of the effect of TMS is due to the noise and sensation it elicits
3. sham TMS - noise but no stimulation, does not control for somatosensory component
4. better with a control site, but sometimes its difficult to ensure that the control site has equivalent somatosensory and auditory effects to test site

Question 21

TMS other limitations

Answer 21

1. the effects of TMS on the brain are limited to the cortex, TMS cannot reach deeper cortical and subcortical regions/structures
2. the effects of TMS on behaviour/performance are much more subtle and hence can be harder to detect than the effects of neurological damage
3. although it is generally very safe, it is associated with a small risk of eliciting seizure, so low levels of stimulation is used and participants are carefully screened