Neuroscience Methods II Flashcards
Application of structural MRI
Study of brain plasticity
processes underlying MRI
role of the magnet - Because of the high water content of soft tissue, there are abundant protons which are in rotatory motion
how structural contrast in MRI can be generated on the basis of…
increasing longitudinal magnetization after the radiofrequency pulse
to identify brain areas that support sensory and cognitive processes, and to derive models of brain function in fMRI we have to overcome
· Problem one: how to measure neural activity in functional contrast?
· Problem two: how to generate measurable functional contrast in an experiment?
· Problem three: how to identify functional contrast in fMRI raw data?
How to measure T2* Contrast
depends on contrast of deoxygenated to oxygenated haemoglobin
T2* decay also varies with
the functional state of tissue
an increased concentration of oxy-hemoglobin…
makes the T2* decay slower, leading to increased MR signal intensity
Main components of structural MRI machine
magnet, gradient coils, and radiofrequency coil
Limitations for Blood Oxygenation Level Dependent (BOLD) response
participant’s fatigue because it takes a long time to record the necessary number of repeat responses
meaning that the slow BOLD responses to individual stimuli overlap
fMRI block design advantages
good statistical power
robust
continuous activation
fMRI block design disadvantages
inflexible
limited number of conditions
Event-related designs advantages
avoids habituation
analyse subtypes of responses such as correct/incorrect
Event-related designs disadvantages
reduced sensitivity to neural events
Talairach limitations
based on a single brain and a single hemisphere
based has likely changed in the process of fixation
Talairach advantages
procedure for Talairach co-ordinates is highly standardized and can therefore facilitate comparison of results from multiple studies
fMRI limitations
fMRI analysis has low power
null results are almost impossible to interpret, in particular null results do not justify a conclusion like “region is not involved with task“
statistical maps depend on amplitude and noise so out of two regions with the same level of activation but different levels of noise one could be labelled as activated, the other as not activated
Studying association
Damage to a single brain region, but multiple deficits (in typical combination, as a syndrome)
Studying dissociation
Damage leads to impaired performance in task A but performance in task B is normal
simultanagnosia
in a visual scene patients can only see one item at a time
optic ataxia
the inability to accurately point to or reach for objects under visual guidance with intact ability when directed by sound or touch despite normal strength
optic apraxia
inability to turn the eyes voluntarily in a horizontal manner
a failure to make certain eye movements
Three symptoms of Balint’s syndrome
simultanagnosia
optic ataxia
optic apraxia
