Problem 4 Flashcards
Distinction between techniques
- x-ray based
- radio-activity based
- magnetic-field based
- Electricity based
X-ray based
Types
- contrast x-ray
- conventional x-ray
- CT-Scan
Radio-activity based
Types
invasive
- PET
- cerebral angiography
- autoradiography
Magnetic-field based
Types
non-invasive
- MEG
- MRI
- fMRI
- TMS
- DTI
Electricity-based
Types
- Transcranial direct current stimulation (TDCS)
- EEG
- event related potentials (ERPs)
- patch-clamp / single-unit recording (invasive)
Instruments needed for Stereotaxic Surgery
- Stereotaxic atlas
- Stereotaxic Apparatus
Stereotaxic Surgery
Procedure
- Researcher obtains coordinates from atlas
- Anesthesize animal + place in apparatus
- Cut scalp open
- Locate bregma, drill hole in scull, lower device into brain, make lesion
Stereotaxis
Ability to locate objects in space
Histological Method
Procedure
- Perfusion = blood in tissue is removed and replaced with a different fluid
- Brain is removed from skull
- Brain is placed in a fixative
- Brain is sliced into thin sections with microtome or cryostat
- Slices are attached to glass microscope slides
- Tissue is stained to reveal cellular + intracellular structures
Microtome
- platform on which one puts the tissue (includes attachment that freezes brain )
- mechanism that advances the knife
Cryostat
similar to microtome
–> cutting process occurs within a freezer
Anterograde labeling method
tracing afferent axons of the VMH
–> axonal projections from source to termination
Retrograde labeling method
tracing efferent axons of the VMH
–> axonal projections from source to termination
Afferent Axons
axons going into the VMH
Efferent Axons
axons leaving the VMH
Antero-/Retrograde labeling method
Procedure
- Injecting PHA-L into VMH by stereotaxic apparatus
- -> PHA-L is a chemical that is taken up by dendrites and brought to buttons
- Histological Method is used
- Immunocytochemical method = method to make chemicals (PHA-L) visible
- -> Slices are placed in solution containing the antibody
- -> Antibodies attach themselves to their antigen
- Examining slices with microscope
- -> one sees which parts of the brain contain antigen
Computerized Tomography
CT-Scan
- Head is placed in large donut shaped ring
- -> Ring : x-ray tube, x-ray detector which are on opposite sides
- Beam passes through head and scans it from all angles
- Detector measures amount of radioactivity
- Computer translates information received from detector into pictures of skull
- -> usually non-invasive, can however be invasive when special fluid is injected to color brain regions of interest
- -> images are black and white, lowest spatial resolution
Magnetic resonance imaging
MRI
- uses magnetic field to image the living brain
- detects changes in blood flow and therefore identifies regions of the brain that are particularly active during a given task
- distinguishes between regions of gray and white matter
Diffusion tensor imaging
DTI
- uses information about movement of water molecules to visualize small fiber bundles (images of white matter tracts)
- -> modified form of MRI
Single-Unit Recording
Goal
Recording the activity of single neurons over a long period of time in unanesthesized animals
Single-Unit Recording
Procedure
- Implanting electrodes in brain through stereotaxic surgery
- After recovery from surgery, recording system is activated
- -> Ability to observe animals behavior and corresponding activity of the neurons of interest at the same time
- Detected electrical signals are amplified
- Signals can be saved + displayed on a computer
Microelectrodes
- made of thin insulated wire, bare tip
- used to record the electrical activity of individual neurons
Macroelectrodes
- used to record the electrical activity of a brain region as a whole
- electrodes are either implanted
- -> into brain via stereotaxic surgery
- -> unto surface of brain
- -> attached to scalp with special paste
Electroencephalogram
EEG
- recordings made with macroelectrodes which are implanted
- -> detect the source of abnormal activity
Polygraph = plots the changes in voltage, detected by electrodes, along a timeline
Magnetoencephalography
MEG
Records neuronal activity
- performed with neuromagnetometers
- computer examines their output + calculates the source of the particular signals in brain
Neuromagnetometer
device that contains an array of several SQUIDs
SQUID
can detect minute magnetic fields
Position emission tomography
PET
Computerized method of detecting chemical/metabolic changes
- Injecting radioactive 2DG
- ->chemical rapidly breaks down and leaves cell
- -> safety reasons: chemical decays +looses RA quickly
- Persons head is placed in CT-like scanner
- Decay of 2DG
- -> emission of positrons, whose destruction in turn results in release of 2 photons who depart in opposite directions
- Sensors around persons head detect photons
Scanner plots the location from where they were emitted - Computer produces a picture of the slice from this information
=> very expensive, images are colored
Cyclotron
chemicals for PET are produced here
Functional MRI
fMRI
Brain activity is measured indirectly by detecting levels of oxygen in blood vessels
--> highest spatial resolution
Transcranial magnetic stimulation
TMS
Artificially changing the activity of the brain regions of interest to see what effects these changes have on behavior
Use of coil wires arranged in 8-shape
–> middle of 8 is located immediately above region of interest
Microdialysis
What
- Process in which substances are separated by means of an artificial membrane which is permeable to only some molecules
- Method is extremely sensitive and can therefore detect neurotransmitters
Microdialysis
Procedure
- Stereotaxic Surgery is used to place micro dialysis probe in animals brain
- small amount of solution (similar to extracellular fluid) is pumped through one of the tubes into dialysis tubing
- Solution circulates through dialysis tubing, collects molecules from EC fluid from brain, passes through other tube
- Solution is taken from second tube for analysis
MRI
Procedure
- Patient lies down on movable table that slides into opening of a tube
–>All the protons in the brain’s tissues line up in parallel, instead of in their usual random
orientations - MRI machine creates strong magnetic field around the patient and radio waves are directed at the body.
- When pulse is turned off – Protons relax back to their original configuration, emitting radio waves as they go.
- -> Emitted radio frequency energy measured by detectors ringing the head varies, depending on the density of various tissues.
- Computer uses this density-based information to generate a detailed cross-sectional map of the brain.
Spatial Resolution
Ability to detect and represent differences in spatial location
Temporal Resolution
Relates to the duration of time for acquisition of a single frame of a dynamic process
