Lecture 2 - Methods Flashcards
behavior correlations with lesions
This has been the basis for many studies, relying as much as possible on focalized injuries (e.g., strokes, head injuries, and occasionally tumors). CT imaging and structural MRI also are used to verify lesions.
The gold standard to determine extent of damage has been autopsy, although functional deficits i.e., due to metabolic disorders) are not apparent on these. The gold standard for behavioral effects is neuropsychological testing.
Chemical interventions on behavior
E.g., Trost et al., (2006) carried out a study in which healthy volunteers were provided with a “haloperidol challenge” (that is, given an infusion of a dopamine D2 antagonist), compared to two occasions (before and after the active trial, subjects were blind to this) when they were only given saline. They were then tested for cognitive and motor functions thought to be mediated primarily by D2 receptors. They found that functions thought to be D1 mediated (working memory using 2-back) were unaffected, while set shifting (WCST) and resistance to distraction (TAP task) worsened.
Dichotic listening
Using earphones to direct sound to one ear or the other, hemispheric aysmmetry for speech can be tested, since people usually have a right ear advantage (Kimura, 1961). Sometimes this is used to assess for integrity of the corpus callosum.
Tachistoscopic presentation
Stimuli are presented very briefly, for microseconds, faster than the eyes can move. Since the eye cannot fixate in another area of the picture, the input is selectively processed first in one hemisphere. Useful in assessment of individuals with severed corpus callosum to assess functions of each hemisphere (e.g., Gazzaniga and split brain patient).
Computers have replaced the old T- scopes, such as the one pictured above.
EEG
Electrical recording from multiple electrodes placed on the surface of the head (cortex is found directly below the surface), which reflects the entrained action of thousands of neurons directly underneath. The cumulative voltage over time is expressed in waves that are designated according to their frequency (e.g., fast waves indicative of wakefulness are beta waves, slow waves occurring during sleep or coma are theta waves).
EEG is typically used to assess for epilepsy and sleep disorders.
Inexpensive and non-invasive.
evoked potentials
This is a positive deflection that occurs at approximately 300 milliseconds after a sensory event, and is thought to reflect a cognitive process, a sort of “ah ha” moment of realization. It is seen as an index of information processing speed. It occurs later in older populations, individuals with SUDs, and in dementias.
Delayed EPs in response to sensory and motor events can indicate areas in spinal cord, midbrain and above that are affected.
Structural vs. functional imaging
structural (CT, MRI, DTI, DSI)
functional (fMRI, PET, MET, DfMRI, fNIRS)
Magnetoencephalography (MEG)
Technique which amplifies brain electrical signals (ionic flow in dendrites occurring due to neurotransmission) while muting environmental signals, using highly sensitive superconducting quantum interference devices, or SQUIDs. About 50,000 active neurons are required to generate a detectable signal. Due to the weakness of the signal, it is mostly the large, pyramidal cells in cortex that are recorded.
Transcranial magnetic stimulation
“TMS uses electromagnetic induction to generate an electric current across the scalp and skull without physical contact. A plastic-enclosed coil of wire is held next to the skull and when activated, produces a magnetic field oriented orthogonal to the plane of the coil. The magnetic field passes unimpeded through the skin and skull, inducing an oppositely directed current in the brain that activates nearby nerve cells in much the same way as currents applied directly to the cortical surface.[52]
The path of this current is difficult to model because the brain is irregularly shaped and electricity and magnetism are not conducted uniformly throughout its tissues. The magnetic field is about the same strength as an MRI, and the pulse generally reaches no more than 5 centimeters into the brain unless using the Deep TMS variant of TMS.[53] Deep TMS can reach up to 6 cm into the brain to stimulate deeper layers of the motor cortex, such as that which controls leg motion.[54]”
deactivation of cortical areas (research)
Treatment of depression
CT scan
Computer software generates a 3D image of the brain from a series of 2D X-rays taken around an axis of rotation. The word "tomography" is derived from the Greek tomos (volume) and graphein (to write
pixel
two dimensional unit based on matrix size and field of view
voxel
three dimensional unit based on matrix size, field of view, and slice thickness
MRI
provides 3D structure of the brain, relies on a strong magnet
fMRI
Functional magnetic resonance imaging or functional MRI (fMRI) is a functional neuroimaging procedure using MRI technology that measures brain activity by detecting changes associated with blood flow.[1][2] This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.[3]
PET scan
A method involving injection of a radioactive isotope (molecule that binds to a receptor) to visualize neurotransmitter binding.
Is invasive and has risks, is also quite expensive ($2-5K).
