Methods of Studying The Nervous System

1. Methods of Studying The Nervous System Ch. 5 Pinel's Biopsychology, 5th Ed.

2. Outline • Summary of Previous Lecture • Methods of Visualizing the Living Human Brain a. Contrast X-rays b. Computerized Axial Tomography c. Magnetic Resonance Imaging d. Positron Emission Tomography e. Functional MRI f. Magnetoencephalography (3) Recording Psychophysiological Signals a. Scalp Electroencephalography b. Measures of Somatic Nervous System Activity c. Autonomic Nervous System Activity Pinel's Biopsychology, 5th Ed.

3. Methods of Visualizing the Living Human Brain Pinel's Biopsychology, 5th Ed.

4. Contrast X-rays • To take an X-ray photograph of an object, a beam of x-rays is passed through it onto a photographic plate; any part of the object that absorbs X-rays differently than does the surrounding medium will be distinguishable Pinel's Biopsychology, 5th Ed.

5. Contrast X-rays • Standard X-rays can’t be used for studying the brain because the brain is composed of many overlapping structures that all absorb X-rays to about the same degree • Contrast X-rays solve this problem in some cases; a radio-opaque material is introduced into the structure of interest to make it “stand out” from the others on an X-ray photograph Pinel's Biopsychology, 5th Ed.

6. Contrast X-rays • For example, in cerebral angiography a radio-opaque dye is injected onto the carotoid artery; it reveals displacement or enlargement of blood vessels Pinel's Biopsychology, 5th Ed.

7. Computerized Tomography(CT) • Provides a 3-dimensional view of structure • The X-ray gun and the X-ray detector rotate in apposition around the brain at one level taking a series of measurements from which an image of one section is constructed; this is repeated at multiple levels • The CT-scan image of the brain is not high spatial resolution Pinel's Biopsychology, 5th Ed.

8. Computerized Tomography(CT) Pinel's Biopsychology, 5th Ed.

9. Magnetic Resonance Imaging (MRI) • It has highest spatial resolution • The images are created from measurements of the waves emitted by hydrogen atoms when they are placed in a magnetic field • Its clarity stems from the fact that neural structures differ considerably in their density of hydrogen atoms Pinel's Biopsychology, 5th Ed.

10. Magnetic Resonance Imaging (MRI) Pinel's Biopsychology, 5th Ed.

11. Positron Emission Tomography (PET) • A method of highlighting brain areas that are active, rather than equally showing all brain structures • The patient is injected with radio-active 2-deoxyglucose; because 2-DG is structurally similar to glucose, it is taken up by neurons as if it were glucose (This is somewhat invasive, although not as invasive as lesion surgery, etc.) Pinel's Biopsychology, 5th Ed.

12. Positron Emission Tomography (PET) • More active neurons need more energy and take up more 2-DG; unlike glucose, 2-DG cannot be metabolized by neurons and it accumulates in them Pinel's Biopsychology, 5th Ed.

13. Positron Emission Tomography (PET) • The patient is injected with radio-active 2-DG and then engages in the activity under study (e.g., reading) while a PET scan of the brain is being taken • The PET scan reveals on a series of images of horizontal sections where radio-activity has accumulated, and thus it indicates what areas were particularly active during the test Pinel's Biopsychology, 5th Ed.

14. Positron Emission Tomography (PET) Pinel's Biopsychology, 5th Ed.

15. Functional Magnetic Resonance Imaging (fMRI) • Allows brain activity to be measured by imaging the increase in oxygen (blood flow) that occurs to brain areas that are active • Surplus of blood occurs are active sites Pinel's Biopsychology, 5th Ed.

16. Functional Magnetic Resonance Imaging (fMRI) • It’s four advantages over PET include: (1) nothing must be injected into the subject (2) one image provides structural and functional information (3) the spatial resolution is better (4) changes can be measured in real time (although, the temporal resolution is poor compared to ERP (EEG)) Pinel's Biopsychology, 5th Ed.

17. Magnetoencephalography (MEG) • Measure brain activity in terms of changes in magnetic fields measured on the surface of the scalp • Good temporal resolution (although EEG gives best temporal resolution) Pinel's Biopsychology, 5th Ed.

18. Transcranial magnetic stimulation (TMS) • Hard to establish cause and effect with PET, fMRI, and MEG, just associations • TMS uses magnetic field under a coil to momentarily turn off brain activity • We can then see how “blocking” the brain area affects cognition • Safety and permanent damage is not ascertained Pinel's Biopsychology, 5th Ed.

19. Transcranial magnetic stimulation (TMS) Hmmm… Pinel's Biopsychology, 5th Ed.

20. Recording Psychophysiological Signals Pinel's Biopsychology, 5th Ed.

21. Scalp Electroencephalography (EEG) • An EEG signal is measured through an array of scalp electrodes • EEG waves reflect the sum total of all the electrical events in the head (action potentials, eye movements, blood flow, etc.) thus, the EEG reveals little about the nature of the underlying neural activity Pinel's Biopsychology, 5th Ed.

22. Scalp Electroencephalography (EEG) • Its value lies in the fact that particular EEG wave forms are associated with particular states of consciousness; generally low-amplitude, fast EEG activity is associated with alert aroused state; and high-amplitude, slow EEG activity (alpha waves) is associated with a relaxed but awake state Pinel's Biopsychology, 5th Ed.

23. Scalp Electroencephalography (EEG) • EEG can be used to study brain activity in real time, in response to specific events. These are called evoked potentials • Usually many evoked potentials are used to generate an averaged evoked potential in order to reduce the noise of the background EEG activity Pinel's Biopsychology, 5th Ed.

24. Scalp Electroencephalography (EEG) • A subset of evoked potentials are event-related potentials (ERPs), which are time-locked evoked potentials, meaning that the EEG in response to an event is always measured during a specific interval of time • For example: an ERP of P300 (positive amplitude at 300 miliseconds) always occurs when a stimulus has semantic meaning to a subject Pinel's Biopsychology, 5th Ed.

25. Pinel's Biopsychology, 5th Ed.

26. Event Related Potentials(ERPs) Pinel's Biopsychology, 5th Ed.

27. Event Related Potentials(ERPs) • ERPs have good temporal resolution, but poor spatial resolution Pinel's Biopsychology, 5th Ed.

28. Scalp Electroencephalography (EEG) • EEG recording are a valuable diagnostic tool; for example the presence of high-amplitude spikes in the EEG (i.e., epileptic spikes) is the primary criterion for diagnosing epilepsy Pinel's Biopsychology, 5th Ed.

29. Measures of Somatic Nervous System Activity • Muscle tension: • An electromygram (EMG) is the changing difference in the voltage between two large electrodes placed on the skin above a large muscle; the amplitude of EMG signals indicates the combined level of tension in the underlying muscle • The raw signals are usually integrated so that the data are easier to work with; the height of the curve of integrated EMG activity indicates the number of spikes on the EMG signal per unit of time Pinel's Biopsychology, 5th Ed.

30. Measures of Somatic Nervous System Activity • Eye movement: • in an electrooculogram (EOG) eye movements are recorded by placing four electrodes around the eye; the signals result from the fact that the front of the eye is more positively charged than the back • The direction of movement can be inferred from the relation between the activity recorded on two channels: (1) above vs. below and (2) left vs. right Pinel's Biopsychology, 5th Ed.

31. Autonomic Nervous System Activity • Skin conductance: • Skin conductance level (SCL) is the general level of skin conductance associated with a particular situation • A skin conductance response (SCR) is a rapid change in skin conductance in response to a particular event; one application is the lie detector test (break) Pinel's Biopsychology, 5th Ed.

32. Websites • A Primer for CAT and MRI: http://www.med.harvard.edu/AANLIB/hms1.html • The Electroencephalogram: http://www.medfak.uu.se/fysiologi/lectures/EEG.html Pinel's Biopsychology, 5th Ed.

33. Methods of Studying The Nervous System Ch. 5 cont’d Pinel's Biopsychology, 5th Ed.

34. Outline (1) Invasive Physiological and Pharmacological Methods a. Stereotaxic Surgery b. Lesion Methods c. Electrical Stimulation d. Electrical Recording Methods e. Pharmacological Methods (2) Genetic Engineering a. Knockouts b. Gene replacement Pinel's Biopsychology, 5th Ed.

35. Invasive Physiological and Pharmacological Methods • In most cases, laboratory animals serve as the subjects when invasive procedures are required to directly manipulate or measure the brain Pinel's Biopsychology, 5th Ed.

36. Stereotaxic Surgery • The first step in may invasive biopsychology experiments is stereotaxic surgery; it allows accurate placement of lesions, probes, electrodes, and other devices into the brain Pinel's Biopsychology, 5th Ed.

37. Stereotaxic Surgery • The method employs a stereotaxic atlas (3-D map of brain) and a stereotaxic instrument (head holder and electrode holder) • The reference point is often bregma (the point where two main plates of the rat skull naturally fuse together) Pinel's Biopsychology, 5th Ed.

38. Stereotaxic Surgery Pinel's Biopsychology, 5th Ed.

39. Lesions • The purpose of lesioning is to eliminate functioning in a certain brain area to see how behavior is affected (can cause-and-effect relationship) Pinel's Biopsychology, 5th Ed.

40. Lesion Methods • The aspiration method is often used to remove cortical tissue through suction • The radio-frequency electrolytic lesion is the most common subcortical lesion; the tissue is destroyed by the heat of the current Pinel's Biopsychology, 5th Ed.

41. Lesion Methods • Sectioning (Small knife cuts) are often used for severing tracts • Cryogenic blockade is like a reversible lesion; the tissue is temporarily cooled to the point that all neural activity in the vicinity of the probe stops; it produces little permanent damage Pinel's Biopsychology, 5th Ed.

42. Lesion Methods • Lesion studies must be interpreted with caution; a lesion inevitably damages structures other than the one that the surgeon targeted, and lesions seldom completely remove a structure that is targeted Pinel's Biopsychology, 5th Ed.

43. Electrical Stimulation • The effects of electrical stimulation are often opposite to those of a lesion to the same brain site • Electrical stimulation research is done prior to any lesioning Pinel's Biopsychology, 5th Ed.

44. Electrical Recording Methods • Intracellular unit recording • Measures changes in the membrane potential of a neuron over time; it requires a microelectrode positioned inside a neuron • It is next to impossible to record intracellularly in a freely moving animal because it is difficult to keep the microelectrode inside the neuron Pinel's Biopsychology, 5th Ed.

45. Electrical Recording Methods • Extracellular unit recording • A microelectrode is positioned near a neuron • The signal is a series of spikes; each spike indicates an action potential from a nearby neuron; spikes of the same amplitude are assumed to come from the same neuron Pinel's Biopsychology, 5th Ed.

46. Electrical Recording Methods • Multiple unit recording • Multiple unit recording provides an indication of the rate of firing of many neurons in the general vicinity of the electrode tip • An electrode larger than a microelectrode picks up the action potentials from many nearby neurons • The signal is integrated so that the height of the curve indicates the number of action potentials in the vicinity per unit of time Pinel's Biopsychology, 5th Ed.

47. Electrical Recording Methods • Invasive EEG recording • Implanted electrodes are used to record EEG in laboratory animals because the scalp electrode do not allow as clear or finite position recording Pinel's Biopsychology, 5th Ed.

48. Pharmacological Methods Pinel's Biopsychology, 5th Ed.

49. Pharmacological Methods • Routes of drug administration include intragastrically (stomach), intraperitonally (abdomen), intramuscularly, subcutaneuously, or intravenously • These peripheral routes all suffer from the fact that many drugs cannot pass the blood-brain barrier; • This problem can be overcome administering drug via stereotaxically positioned cerebral cannula (microinjection of drugs directly into brain tissue) Pinel's Biopsychology, 5th Ed.

50. Pharmacological Methods • Sometimes, drugs can be injected into the brain that produce chemical lesions that are more selective than electrical lesion might be; for example, 6-OHDA is a neurotoxin that selectively destroys dopaminergic and noradrenergic neurons in the vicinity of the injection site Pinel's Biopsychology, 5th Ed.