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1

Distinction between techniques

- x-ray based
- radio-activity based
- magnetic-field based
- Electricity based

2

X-ray based
(Types)

- contrast x-ray
- conventional x-ray
- CT-Scan

3

Radio-activity based
(Types)

invasive

- PET
- cerebral angiography
- autoradiography

4

Magnetic-field based
(Types)

non-invasive

- MEG
- MRI
- fMRI
- TMS
- DTI

5

Electricity-based
(Types)

- Transcranial direct current stimulation (TDCS)
- EEG
- event related potentials (ERPs)
- patch-clamp / single-unit recording (invasive)

6

Instruments needed for Stereotaxic Surgery

- Stereotaxic atlas
- Stereotaxic Apparatus

7

Stereotaxic Surgery
(Procedure)

1. Researcher obtains coordinates from atlas

2. Anesthesize animal + place in apparatus

3. Cut scalp open

4. Locate bregma, drill hole in scull, lower device into brain, make lesion

8

Stereotaxis

Ability to locate objects in space

9

Histological Method
(Procedure)

1. Perfusion = blood in tissue is removed and replaced with a different fluid

2. Brain is removed from skull

3. Brain is placed in a fixative

4. Brain is sliced into thin sections with microtome or cryostat

5. Slices are attached to glass microscope slides

6. Tissue is stained to reveal cellular + intracellular structures

10

Microtome

- platform on which one puts the tissue (includes attachment that freezes brain )

- mechanism that advances the knife

11

Cryostat

similar to microtome
--> cutting process occurs within a freezer

12

Anterograde labeling method

tracing afferent axons of the VMH
--> axonal projections from source to termination

13

Retrograde labeling method

tracing efferent axons of the VMH
--> axonal projections from source to termination

14

Afferent Axons

axons going into the VMH

15

Efferent Axons

axons leaving the VMH

16

Antero-/Retrograde labeling method
(Procedure)

1. Injecting PHA-L into VMH by stereotaxic apparatus
--> PHA-L is a chemical that is taken up by dendrites and brought to buttons

2. Histological Method is used

3. Immunocytochemical method = method to make chemicals (PHA-L) visible
--> Slices are placed in solution containing the antibody
--> Antibodies attach themselves to their antigen

4. Examining slices with microscope
--> one sees which parts of the brain contain antigen

17

Computerized Tomography
(CT-Scan)

1. Head is placed in large donut shaped ring
--> Ring : x-ray tube, x-ray detector which are on opposite sides

2. Beam passes through head and scans it from all angles

3. Detector measures amount of radioactivity

4. 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

18

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


19

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

20

Single-Unit Recording
(Goal)

Recording the activity of single neurons over a long period of time in unanesthesized animals

21

Single-Unit Recording
(Procedure)

1. Implanting electrodes in brain through stereotaxic surgery

2. 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

3. Detected electrical signals are amplified

4. Signals can be saved + displayed on a computer

22

Microelectrodes

- made of thin insulated wire, bare tip

- used to record the electrical activity of individual neurons

23

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

24

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

25

Magnetoencephalography
(MEG)

Records neuronal activity

- performed with neuromagnetometers

- computer examines their output + calculates the source of the particular signals in brain

26

Neuromagnetometer

device that contains an array of several SQUIDs

27

SQUID

can detect minute magnetic fields

28

Position emission tomography
(PET)

Computerized method of detecting chemical/metabolic changes

1. Injecting radioactive 2DG
-->chemical rapidly breaks down and leaves cell
--> safety reasons: chemical decays +looses RA quickly

2. Persons head is placed in CT-like scanner

3. Decay of 2DG
--> emission of positrons, whose destruction in turn results in release of 2 photons who depart in opposite directions

4. Sensors around persons head detect photons
Scanner plots the location from where they were emitted

5. Computer produces a picture of the slice from this information

=> very expensive, images are colored

29

Cyclotron

chemicals for PET are produced here

30

Functional MRI
(fMRI)

Brain activity is measured indirectly by detecting levels of oxygen in blood vessels

--> highest spatial resolution