brain imaging Flashcards
How is a CT image of the brain produced? What are some of the uses of this type of image?
Tissues of different density differ in the level of X ray absorbsion.
•Image is contrast-reversed:
•Denser areas appear lighter
•Grey and white matter contrast isn’t great
How do white matter, grey matter and cerebrospinal fluid have different brightness in a structural MR image?
Because the contrast is not that good – looks at density not colour.
On T1 images FAT is white. On T2 images both FAT and WATER are white. On T1 images FAT is white.
what is T1 and T2?
The two basic types of MRI images are T1-weighted and T2-weighted images.
T1 differs depending on which type of tissue the hydrogen is embedded in.
How is the flow of blood in the brain tracked using PET?
he scan captures images of the activity of the brain after radioactive “tracers” have been absorbed into the bloodstream. These tracers are “attached” to compounds like glucose (sugar).
and
Because tissues differ in magnetic properties
what is a BOLD signal
Blood-oxygen-level-dependent
the BOLD signal derives from magnetic field perturbations within and around small blood vessels, caused by dHb. Because it contains unpaired electrons, which have a strong magnetic dipole moment, dHb is paramagnetic; it strongly perturbs the surrounding magnetic field.
How is the BOLD signal generated?
The signal arises in the fact that neural activity is accompanied by changes in the level of oxygenated and de-oxygenated blood in the vicinity.
This relationship is called the haemodynamic response. A spurt of neural activity produces a haemodynamic impulse response function (HIRF) that is both delayed relative to the neural activity and more spread out in time. The HIRF starts off with a small dip in the signal, which corresponds with a brief excess of de-oxygenated blood in the area. This is followed by a net increase in oxygenated blood, corresponding to the increase in signal level.
When an fMRI image shows certain brain areas ‘lighting up’ when certain psychological operations are being carried out, what in fact does this ‘lighting up’ show?
the activated areas shown in colour are the ones whose activation is specific to the experimental contrast the researcher is interested in. The areas that are not shown by colour coding are not inactive – they are all active but their activation is not as specific to what the researcher is looking for.F
How did Shaywitz et al. demonstrate that women have more bilateral phonological functioning than men?
- did letter-case and rhyme judgement tasks and
- the averages of the brain activity was taken specific to phonological processing
- The fMRI images for male and female phonological processing shows that this activation is strongly lateralised in males but much more bilateral in females. This seems to match with neurological observations of the fact that females who suffer from stroke damage to the left activated areas recover phonological function better/faster than men with the same damage.
How does a semantic priming experiment work
In a semantic priming experiment, participants see two words in each trial – the first is the prime and the second the target. The idea is that, if seeing the prime either excites or inhibits activation of the target, the time to respond will change (i.e., faster or slower, respectively). If the seeing the prime has no impact on processing the target, then we can conclude that the representations of the two words in the participant’s brain are note closely linked.
The key contrast is between prime-target pairs that are associatively related (e.g., cottage – cheese, i.e., mean something together) or simply related by semantic category (e.g., dog – horse; both domesticated animals, often found together in farms).
How do we learn that the RH may have a role in semantic aspects of language processing using this paradigm? (semantic priming)
Patients with RH lesions (whose LH is intact and used for the task) show priming for associative pairs (indicating that LH by itself is good at this), but no priming for semantic pairs (suggesting that LH by itself is no good at this). But normal participants show semantic priming just fine, so RH must be where this plays out. Indeed, doing this experiment on split-brain patients shows that RH can do semantic priming where LH isn’t much good at it.
RH has a profound role in language (and language-based thinking, generally) because language without strong semantic linkages would be greatly impoverished indeed.
Give some examples of how we use physical metaphors in abstract thinking.
Intensely body-referential our expressions of abstract content can be. These sentences use a very visceral way of describing pretty abstract things. Is this just a matter of usage, or does it say something quite deep about how we use bodily analogy to think abstract things? Can we think and/or express abstract things without bodily analogy?
phonology
- Phoneme: smallest linguistically significant unit of speech sound / gesture
- /b/ /g/ /a/ /l/ /r/
- Phonetics: study of speech sounds
- Phonology: rules governing phoneme combinations
- /kh/ /a/ (car) but /s/ /k/ /i/ /l/ (skill)
orthology
Orthography: symbol system
• English: alphabetic
• Japanese: syllabic
• Chinese: logographic
morpholoy
Morphology is the study of meaningful units of language, called morphemes, and how they are combined in forming words. For example, the word contradiction can be broken up as contra-dict-ion, with the prefix contra- (against), the root word dict (to speak), and the suffix – ion (a verbal action).
grapheme
Graphemes are the smallest units in a writing system capable of causing a contrast in meaning. In the English alphabet, the switch from cat to bat introduces a meaning change; therefore, c and b represent different graphemes.
