BIO210 Weekly Guide #12
CNS ACTIVITY
AND FUNCTIONAL MEASURES
After completing this laboratory you should be able to:
1) Sketch several basic reflex arcs and describe the function of each
2) Describe the basic pattern and variations of lateralization of cerebral function
3) Describe the anatomical and physiological basis of the human electroencephalogram (EEG)
4) Describe and delineate the major EEG frequency bands
5) Describe the characteristic electrophysiological correlates of waking and sleep stages
6) Explain what an averaged evoked potential (AEP) or event-related potential (ERP) is
Guide to Gross Anatomy Guide to Histology Guide to Physiology
Outline
I. Reflex arcs
A. Definition - what is a reflex?
B. Spinal reflexes
stretch reflex
pain withdrawal reflex
crossed extensor reflex
C. Cranial reflexes
blink reflex
pupillary light reflex - direct and consensual
vestibulo-oculomotor reflex
II. Cerebral Lateralization
A. Definition - What is brain lateralization?
B. Left and Right Hemisphere Functions
left hemisphere - analytical, language, computation
right hemisphere - synthetic, holistic, spatial, recognition
C. Gender and lateralization
D. Handedness and lateralization
E. Experimental evidence
brain injury - Broca
"split-brain" patients - Roger Sperry
tachistoscopic studies
III. The electroencephalogram (EEG)
A. Anatomical and physiological substrates
generation of cortical field potentials
recording cortical field potentials
B. EEG frequency bands
delta - 0-4 Hz
theta - 5-7 Hz
alpha - 8-12 Hz
low beta - 13-25 Hz
high beta - >25 hz
C. Spatial and temporal distributions
spatial distributions
broad- vs. narrow band
functional significance
D. EEG and sleep stages
measures:
EEG, EOG, EMG, arousability
states and stages:
waking, alert state
relaxation
hypnogogia
NREM sleep stages
REM sleep
Gross Anatomy List
None for this section.
Guide to Gross Anatomy
None for this section.
Guide to Histology
None for this section.
Guide to Physiology
Reflexes and Neurological Tests
A. Patellar and Achilles Reflexes
1) Seat the subject on the edge of the lab table, with both legs hanging free.
2) Using the rubber hammer, lightly tap each leg just below the kneecap. If you do this correctly, the tapped leg should jerk forward.
3) Now passively dorsiflex the subject's foot, then tap lightly on the Achilles tendon (tendocalcaneous). The ankle should plantar flex in response.
Q1: Can you describe the neural mechanism underlying these reflexes and why they are essential for standing postural balance?
B. Biceps and Triceps Reflexes
1) Seat the subject in a chair. Have her hold both arms out in front of her with her palms up and her elbows lightly bent.
2) Support each arm just above the elbow. Using the rubber hammer, lightly tap on each distal biceps tendon, just above the inside of the elbow.
3) Now have the subject turn each arm over (pronating) and again support the arm just above the elbow. Tap lightly on each distal triceps tendon just above the olecranon.
Q2: Did the responses match your predictions?
C. Babinski and Hoffman Signs
1) Again, seat the subject on the edge of the lab table, with both legs hanging free.
2) Using your thumbnail, and applying light pressure, stroke the lateral (little toe) side of the sole of her foot from toe to heel or from heel to toe.
3) Hold the subject's middle finger between your thumb and index finger with your thumbnail against her fingernail. Ask her to relax her hand. Slide your thumb down until your thumb nail "clicks" off the end of her fingernail.
Q3: Did her toes plantar flex (towards the sole) or fan out and dorsiflex (towards the top of the foot)? Was there a reflexive twitch of her fingers when your thumbnail clicked off of her fingernail? What would toe dorsiflexion or a finger contraction indicate?
D. Direct and Consensual Photopupillary Reflexes
1) Seat the subject in a darkened (but not completely dark!) room and sit opposite her where you can clearly see her pupils. Allow at least 2 minutes for her eyes to adapt to the dark and for her pupils to dilate. Hold the penlight about 6 inches from the bridge of her nose and flash the light for about 1/2 second.
Q4: Did both pupils constrict? Did they constrict evenly?
2) Now have the subject hold a piece of dark construction paper up as a shield between her two eyes. The subject should continue to look straight ahead. Hold the penlight off to the subject's right side and flash it again, so that only her right eye is illuminated.
Q5: Did both pupils constrict? Did they constrict evenly? What can you conclude about the relative magnitudes of the direct (illuminated right eye) and consensual (non-illuminated left eye) pupillary reflexes?
E. Vestibulo-oculomotor Reflex
Don't participate in this experiment as a subject if you get motion sickness.
1) Have the subject sit in the swivel chair, tilt her head slightly forward (why?), grasp the bottom of the chair, close her eyes, and hang on. Spin the chair clockwise through at least ten full rotations.
2) Stop the chair and have the subject immediately open her eyes, hold her head up, and fixate (look directly at) a point behind your (the experimenter's) shoulder. Closely observe the motion of her eyes. Her eyes should go through a series of jerky tandem motions as they both drift slowly in one direction and then saccade rapidly back in the opposite direction.
Q6: Do the drifts or saccades match the direction of the original spin? What is the subject's visual perception, i.e. what direction does the world seem to be moving to the subject?
Q7: Why does this process promote disorientation, vertigo, and nausea?
Q8: Can you explain both the neural mechanics and the practical functional significance of this reflex?
3) If you are having trouble understanding what is going on inside of the semicircular canals, try the following experiment. Spin a raw egg on the table. Stop the egg with your hand, then immediately let go. The egg should "magically" start spinning again, due to the rotational inertia of the fluid contents.
F. Just for Fun
1) Sit comfortably in a chair with both feet on the ground.
2) Raise your right foot a few inches off of the floor, then rotate it in clockwise circles.
3) While continuing to rotate your foot, trace the number 6 in the air with your right hand.
Q9: What happened to the motion of your foot as soon as you started moving your hand?
Electroencephalogram
The equipment needed at this station includes a PowerLab/PC station, a Dual BioAmp, 1 ElectroCap, and 2 shielded reference leads with ear clips.
A. Resting EEG
1) The following transducers should be connected to the PowerLab box (if they aren't, then connect them):
CH1 - BioAmp A (with cable and 3 EEG leads)
CH2 - BioAmp B (with cable and 3 EEG leads)
2) Hookup the subject to the PowerLab, using the following guide (color codes refer to the colored markings on the gray BioAmp cable):
3) Prepare each ear lobe by cleaning it thoroughly with an alcohol swab, then rubbing it with some "Omni" solution, as demonstrated by the instructor. Clip the BLUE A1 earclip electrode to the LEFT earlobe and the WHITE A2 earclip electrode to the RIGHT earlobe. The metal cup of each electrode goes on the outer surface of the earlobe. Use the blunt syringe to fill the cup of each electrode with electro-gel. Secure each electrode with paper tape.
4) Attach the rainbow-colored elastic chest band around the upper chest of your subject with the snaps in the front.
5) Slip foam "doughnut" pads to each of the two front polar (FP1 and FP2) electrodes on the ElectroCap. The sticky side of the electrode goes toward the cap.
6) Position the ElectroCap on the head of the subject. Make sure that the cap is centered on the head, with the foam pads at the front. The two foam pads should rest ~1" above the subject's eyebrows.
7) Snap the two staps to the chest band, crossing them over in the front.
8) Find the electrodes labeled O1, O2, T3, T4, and GND. O1 and O2 will be over the occipital lobes about 1" above and to either side of the "inion"(the depression at the base of the occipital bone on the back of the head). T3 and T4 will be above the temporal lobes about 1 inch directly above the left and right ear, respectively. GND will be over the center of the head, just in back of where the cables come out of the cap.
9) Apply some Omni to the wooden end of a sterile swab, stick it through the hole in the O1 electrode and gently abrade the scalp. What you are trying to do is get rid of most of the dead skin cells, and a bit of the epidermis. Try to almost, but not quite, draw blood. Repeat this process for the O2, T3, T4, and GND electrodes. Fill all five of these electrodes with ElectroGel, using the blunt syringe. This may sting a bit for the subject.
10) Have the subject get comfortable, put her hands lightly on her knees, and RELAX.
11) Turn on the PowerLab box and the PCh. Select the ML Human EEG alias on the desktop and launch it. The two channels have been set up and labeled for you. Notice that Channel 1 is labeled as Occipital and channel 2 is labeled as Temporal. Notice also that the display settings involve some fancy PowerLabisms, such as filters on each channel, a compression of the horizontal scale, and a "smoothing" of each trace. These are necessary to enhance the EEG display.
12) Start the Chart display. Have the subject relax, with her eyes open. It is particularly important for a "clean" recording that the subject not clench her teeth (why?). The resting "beta" EEG should show high-frequency, low amplitude activity on both channels. If it does not, consult with the instructor.
13) Record at least 1 minute of resting EEG activity.
Q10: Is the resting activity for the two channels synchronized?
Q11: Does the resting activity for the two channels look qualitatively similar? Does it have similar overall amplitude and frequency properties?
B. Occipital Alpha and Alpha Blocking
For the following recording, you will need to keep accurate records of exactly when the subject opened her eyes, closed her eyes, etc. so that you can mark and annotate the Chart record.
1) Have the subject relax with her eyes open.
2) Start the Chart display. and record at least 1 minute of resting beta activity.
3) Now instruct the subject to "clear her mind", allow herself to become deeply relaxed, and lightly close her eyes. If you are lucky, one or both channels will shift into higher amplitude, lower frequency (8-12 Hz) sinusoidal oscillations - alpha activity.
4) Record at least 1 minute of this activity. If you are not getting any alpha activity, it is most likely because the subject is not fully relaxed, or because the scalp preparation was inadequate. In either case, try a few more times before consulting with the instructor.
5) If you are getting good alpha, have the subject open her eyes and close her eyes several times, with at least 10 seconds between each action, and observe the record for alpha activity.
6) Finally have the subject relax with her eyes closed, and establish clear alpha activity. Snap your fingers behind her head and observe the recording. Does the click block or suppress alpha activity. Snap your fingers several more times.
Q12: Does the alpha suppression response "habituate" or diminish with repeated stimulations?
Q13: Which recording site (occipital or temporal) shows stronger alpha? Since alpha seems to be most directly blocked by visual input, does this agree with what you know about the site of primary cortical processing of visual information?
C. Cleanup
1) When you are satisfied with your recordings, save the data files.
2) Carefully remove the ElectroCap, chest strap, and earclip electrodes. Clean as much electro-gel as possible from the subject's hair, using gauze pads.
3) Rinse off the ear clip electrodes in water, then swab with an alcohol swab.
4) Immerse the ElectroCap in a sink filled with dilute dish soap.