Experimental Ablation

This presentation covers one of the oldest research methods in Physiological Psychology named Experimental Ablation. The credits for all the content and images goes to Neil R. Carlson's textbook Physiology of Behavior.

1. Experimental Ablation Aleem Ashraf Department of Psychology University of Sindh. Methods & Strategies in Biological Psychology

2. Contents Evaluating the Behavioral Effects of Brain Damage Producing Brain Lesions Stereotaxic Surgery Histological Methods Tracing Neural Connections Studying the Structure of the Living Human Brain Reference 2

3. Experimental Ablation Experiments in which part of the brain is damaged and the animal’s behavior is subsequently observed are called lesion studies or Experimental ablation. 3

4. All regions of the brain are interconnected, it’s hard to interpret the results of such studies. Damage to structure X doesn’t for sure affect structure Y. Evaluating the Behavioral Effects of Brain Damage 4

5. Producing Brain Lesions Brain lesions of subcortical regions are usually produced by passing electrical current through a stainless steel wire that is coated with an insulating varnish except for the very tip . The heat of the current kills the cell in the tissue. All nearby cells including the axons of the passing neurons are destroyed. Called Radio Frequency Lesions. 5

6. Figure 1. Radio Frequency Lesions in rat brain 6

7. Producing Brain Lesions A more selective method of producing brain lesions employs an excitatory amino acid such as kainic acid , which kills neurons by stimulating them to death . Amino acid is injected through a cannula . Lesions produced in this way are referred to as excitotoxic lesions . Does not affect the nearby axons. 7

8. Producing Brain Lesions This selectivity permits the investigator to determine whether the behavioral effects of destroying a particular brain structure are caused by the death of neurons located there or by the destruction of axons that pass nearby. 8

9. Figure 2. Ecitotoxic Lesion in hippocampus of rat brain 9

10. Producing Brain Lesions When we pass an electrode or a cannula through the brain to get to our target, we inevitably cause a small amount of damage to other areas as well. Which makes causal inferences implausible. Sham lesion is produced in the control group to avoid this problem. 10

11. Producing Brain Lesions Sham lesion A placebo procedure that dupli-cates all the steps of producing a brain lesion except the one that actually causes the brain damage . Sometimes researchers don’t cause permanent brain damage to animals. The inject local anesthetic to the target area blocking action potentials. 11

12. Stereotaxic Surgery The process by which an electrode or a cannula is precisely located and produces lesions in a brain is called stereotaxic surgery. Done with an apparatus called stereotaxic apparatus. For precise measurements of brain stereotaxic atlas is used. 12

13. Stereotaxic atlas is a collection of drawings of sections of the brain of a particular animal with measurements that provide coordinates for stereo- taxic surgery . 13

14. Figure 3. Stereotaxic Apparatus 14

15. Figure 4. Stereotaxic Surgery on human brain 15

16. Histological Methods Fixing, slicing, staining, and exami-ning the brain under microscope. These methods are called histological methods. Fixation: To preserve the tissue from decomposing it is placed in a fixative chemical such as formaline . To obtain clear view, the blood is drained prior to fixation (Perfusion) . 16

17. Histological Methods Sectioning: A tissue is then sliced into thin sections to place under microscope. Slicing is done with a microtome. 17

18. Histological Methods After the tissue is cut, the slices are attached to glass microscope slides . The slides are then put in various chem-ical solutions, the process known as staining. Staining is done to give contrast to the tissues under microscope to make the smaller structures clearly visible. The most frequently used is cresyl violet . 18

19. Figure 6. Frontal Section of a cat brain stained with cresyl violet 19

20. Electron Microscopy Transmission electron microscope is used to see the small details of the cells such as synaptic vesicles. Figure 7. Electron Photomicrograph This electron photomicrograph shows a section through an axodendritic synapse . 20

21. Scanning Electron Microscope It provides the images in three dimensions. Figure 8. Neurons & Glial Cells 21

22. Confocal Laser Scanning Micro- scopy It doesn’t require slides. It can work on exposed tissue in living brains Requires florescent dye for staining cells Figure 8. Branches of dendrites of a living mouse 22

23. Tracing Neural Connections Studying isolated brain tissues is not enough. It’s important to understand its connection with other neural circuits. Tracing Efferent Axons : The output from the tissue of interest. Tracing Afferent Axons : The input to the tissue of interest. 23

24. Tracing Efferent Axons A chemical is injected into a tissue of interest. Which is taken up by dendrites and cell bodies and transported through axons to other neurons. The process known anterograde labelling (moving forward). After few days the animal is killed and examined under a microscope. 24

25. Tracing Efferent Axons Once we know that a particular brain region is involved in a particular function, we may ask what structures provide inputs to the region and what structures receive outputs from it . 25

26. Tracing Efferent Axons The antibody molecules are attached to various types of dye molecules. The body’s immune system attacks these antigens. The antibodies attach themselves to their antigens becoming visible under a microscope. This way researcher can trace where the output goes from the tissue of interest. 26

27. Tracing Efferent Axons Using PHA-L (kidney protein) for Tracing Efferent Axons 27

28. Anterograde Tracing Method. PHA-L was injected into the ventromedial nucleus (VMH) of the hypothalamus , where it was taken up by dendrites and carried through the cells’ axons to their terminal buttons. The section shows labeled axons and terminal buttons in the periaqueductal gray matter (PAG). 28

29. Tracing Afferent Axons It is also important to know from where the tissue of interest receives its input from. The process called retrograde label-ling method (moving backward). Chemicals that are taken up by terminal buttons and carried back through the axons toward the cell bodies. 29

30. Tracing Afferent Axons The chemical commonly used in this method ( fluorogold ) is injected into a tissue of interest. Which is taken up by terminal buttons and carried back through the axons toward the cell bodies . After few days the animal is killed and examined under a microscope . 30

31. Retrograde Tracing Method Fluorogold was injected in the VMH, where it was taken up by terminal buttons and transported back through the axons to their cell bodies. The photograph shows these cell bodies, located in the medial amygdala . 31

32. Results of Tracing The figure shows one of the inputs to the VMH and one of the outputs, as revealed by anterograde and retrograde labeling methods . 32

33. Studying the living brain The living brain can be examined with: Computerized tomography ( CT scanners ) Magnetic resonance imaging (MRI scanners ). Diffusion tensor imaging (DTI) 33

34. Computerized Tomography The use of a device that uses a computer to analyze data obtained by a scanning beam of X-rays to produce a two-dimensional picture . The patient has a lesion in the right occipital-parietal area (scan 5). 34

35. Magnetic Resonance Imaging A technique by which the interior of the body can be accurately imaged; involves the interaction between radio waves and a strong magnetic field . 35

36. Diffusion Tensor Imaging It can measure macroscopic axonal organization in nervous system tissues. The computer adds colors to distin-guish different bundles of axons . 36

37. Reference Carlson, N.R. (2011). Physiology of Behavior. (11 th Ed). 37

38. Thank you! 38