Lecture II Flashcards
MRI
Hydrogen atoms respond to magnetic fields and radiofrequency pulses by emitting energy.
Diffusion tensor imaging/DTI
Measures diffusion of water molecules in brain tissue.
Comparing responses to magnetic fields in different directions.
Combine this information into neural fiber bundles.
Following fibers allows to map connections between areas in health and disease.
Structural/anatomcial MRI
image depends on structures like white and grey matter; analyze tissue changes in health and disease.
fMRI
Measures blood flow and oxygenation changes in brain areas.
Low temporal resolution, high spatial resolution.
Active brain areas consume more oxygen, which … the amount of …
To compensate, … is supplied …
Increases the amount of deoxyhemoglobin.
Oxyhemoglobin is supplied more.
Magnetic resonance of … is higher than …
This is measured in the …
Oxyhemoglobin higher than deoxyhemoglobin.
Blood oxygenation level dependent (BOLD) flow.
Active brain areas (5):
Use more oxygen. Increase deoxyhemoglobin. More oxyhemoglobin supply. Magnetic resonance oxyhemoglobin higher. Seen in BOLD response.
2 types of neural activity:
Neural firing/APs = neural output
Synaptic activity/LFPs = neural processing
BOLD signal reflects …, not itself, but the anticipation on …
Synaptic activity, upcoming changes in neural metabolism.
Excitatory NTs cause…
Vasodilation
Inhibitory NTs cause…
Vasoconstriction
BOLD signals arise from NT release and modulate oxyhemoglobin supply:
Excitatory NTs like glutamate cause…
Inhibitory NTs like GABA cause…
Excitatory NTs cause widening of blood vessels (vasodilation) - leading to more oxyhemoglobin to reach the area in which the NT is released.
Inhibitory NTs cause narrowing of blood vessels (vasoconstriction) - leading to less oxyhemoglobin to reach the area in which the NT is released.
Reduction of information occurs through…
Detecting signal changes in image and disregarding constant parts.
Receptor cells
Consist of rods and cones, which convert light to neural activity that is passed onto the middle cell layers.
Middle cell layers
Consist of horizontal, bipolar, and amacrine cells - compress information by interacting with each other and detecting signal changes while ignoring constant parts.
Ganglion cells
Carry information to the brain.
What cells constitute retinal circuitry? (5)
Rods and cones, horizontal, bipolar, amacrine, ganglion cells.
Pathway from light to visual cortex
Light - rods and cones - horizontal cells - bipolar cells - amacrine cells - ganglion cells - optic nerve - thalamus - visual cortex.
By comparing activation of center or surround, decide whether the … cell will either … or … the …
Whether the ganglion cell will either stimulate or inhibit the further carrying of information.
Only center -
Only surround -
Both or none -
Only center - activation/excitation
Only surround - inhibition
Both or none - no special response
Both or none -
Only center -
Only surround -
Both or none - randomly firing
Only center - cell starts firing quickly and stops when stimulus is gone.
Only surround - cell abruptly stops firing, when inhibition goes away, bit of firing. Removing the input causes firing.
Lateral inhibition
Activation of a cell inhibits neighboring cells.
Effect is greater in peripheral vision - acts over greater distances.
Explained by only surround: stimulus appears in surround of other cell and thus stops firing.
2 types of retinal ganglion cells:
Magnocellular (parasol) cells = large receptive fields, responding to larger areas.
Parvocellular (midget) cells = small receptive fields, responding to spatially localized areas.
Parvocellular/midget cells
Form and color, high spatial resolution.
Magnocellular/parasol cells
Motion, more sensitive and faster, low spatial resolution.
Spatial frequency in 2 types of ganglion cells
Parvocellular/midget - high spatial frequency
Magnocellular/parasol - low spatial frequency
Color
Low frequencies: color
High frequencies: luminance
Form
Low spatial frequencies: motion, no edges
High spatial frequencies: only edges
Parvocellular -
Magnocellular -
Koniocellular -
Parvocellular - red-green colors, high acuity
Magnocellular - luminance, stereo, motion
Koniocellular - blue-yellow colors
