Competition restated

1
Competition restated
fMRI Lesson You should decide for yourself
instead of blindly accepting what some authors
claim
2
Which is more difficult?

• Rocket science
• Or
• Brain Surgery

3
Stereotaxic surgery is the first step in many
biopsychological experiments
4
The goal is to place an electrode or some other
device at a specific target site in the brain.
5
This is a small animal (rat) stereotaxic apparatus
Electrode manipulator
Electrode Holder
Ear bars
Incisor bar
U frame
Base plate
6
Stereotaxic Atlas
Step 1 Consult the stereotaxic atlas for
coordinates of the brain area you are interested
in.
7
Step 1a Find the plate that has the brain region
of interest (e.g., the caudate-putamen,
CPu). Note that this plate is a coronal section
0.70 mm (anterior) to Bregma.
CPu
8
Bregma is a landmark on the skull surface where
the coronal suture meets the sagittal suture.
Coronal suture
Sagittal suture
Lambdoid suture
9
Step 1b Determine the coordinates of the point
in the brain where the electrode tip is to be
positioned. Suggestion it is always a good
idea to check the literature to see what
coordinates others have used.
Plane Medial CPu
AP 0.7 mm
ML 2.0 mm
DV 4.4 mm
CPu
AP (anterior-posterior) ML (media-lateral) DV
(dorsal-ventral)
10
Step 2 Use an approved surgical protocol to
anesthetize the animal and prepare for
surgery. Step 3 Mount the animal in the
stereotaxic apparatus by placing incisors over
the incisor bar and gently inserting the ear bars
so that they enter the auditory canal and meatus.
11
Step 4 Clean and incise the scalp exposing the
skull surface. Step 5 use the 3 dials on the
stereotaxic manipulator to place the tip of the
electrode at the Bregma.
12
Step 6 Read the 3 vernier scales corresponding
to the AP, ML and DV dials.
DV dial
AP dial
ML dial
13
How to read a Vernier scale
The 0 line on the Vernier is above 3.1 cm (or
31 mm) on the main scale. To determine the 10th
of a mm, estimate which line on the Vernier scale
lines up best with a line on the main scale.
AP 31.5 mm
Vernier Scale
Main Scale
14
How to read a Vernier scale
Now lets read the ML coordinate.
ML 10.2 mm
Vernier Scale
Main Scale
15
How to read a Vernier scale
And now the DV coordinate.
DV 23.7 mm
Vernier Scale
Main Scale
16
Step 7 Calculate the new coordinates within the
brain relative to the bregma
Coordinates from the stereotaxic atlas
Coordinates just read from the stereotaxic
manipulator
Bregma
Plane
Medial CPu
Plane

31.5 mm
AP
0.7 mm
AP
/-
10. 2 mm
ML
2.0 mm
ML
-
23.7 mm
DV
4.4 mm
DV
17
Step 8 Use the new coordinates to reposition the
electrode. First, do the AP, then the ML on each
side marking each spot.
AP 32.2
ML 11.2
ML 8.2
Step 9 Drill holes through the skull at each
mark.
18
Step 10 Now lower the electrode into the brain
at the new DV coordinate.
Step 11 Either pass current or inject chemical
to make a lesion. Repeat on other side of brain.
19
Step 12 Suture wound and follow postoperative
care procedures. Surgery Complete!
20
Fill in your Name Here
Has successfully completed a 12 step program to
become
A Virtual Brain Surgeon
With all the rights and privileges hereto forth
bestowed
21
This will open the door to many techniques
including

• Lesion methods
• Electrical stimulation and recording
• Central drug infusions

22
Lesion Methods
Electrolytic and radiofrequency current
Current is passed through an electrode to heat
the exposed tip and destroy adjacent tissue.
Electrolytic lesions of the CPu
23
Lesion Methods
Neurotoxin lesions
A chemical is infused through a cannula to
selectively destroy cells and spare fibers of
passage.
Ibotenic acid lesion of hippocampus
24
Lesion Methods
Aspiration Lesion
Cortical tissue is drawn off by suction through a
fine-tipped glass pipette.
Aspiration lesion of amygdala and entorhinal
cortex (monkey)
25
Lesion Methods
Knife cut
Cutting a nerve or tract without severely
damaging surrounding tissue.
Knife cut of the perforant path input to the
hippocampus
26
Lesion Methods
Cryogenic blockade
A method of temporary inactivation (reversible
lesion). Coolant is pumped through a cryoprobe
causing neurons near the tip stop firing. The
temperature is maintained above freezing so that
there is no structural damage.
27
Electrical stimulation
Bipolar electrode
Two insulated wires wound tightly together are
used to deliver weak pulses of current to
increase the firing of neurons near the tip.
Electrical stimulation often elicits behavioral
responses such as eating, drinking, sleeping,
attacking and copulation. The behavioral effects
are usually opposite to those produced by a
lesion.
28
Electrical recording
Intracellular unit recording
Used to study the electrophysiological responses
of a single neuron. Records graded fluctuations
in the neurons membrane potential. Usually
performed on chemically immobilized animals
because it is hard to keep the tip of a
microelectrode positioned inside a neuron in a
freely moving animal.
Extracellular unit recording
Records the action potentials of a neuron through
a microelectrode whose tip is positioned in the
extracellular fluid next to it. It provides no
information on the neurons membrane potential.
Multiple unit recording
Large electrodes are used to pick up signals from
many neurons, adding the total number of action
potentials per unit of time.
29
(No Transcript)
30

• OKeefe Dostrovsky (1971)

31
Fig. 1. Responses of a hippocampal (CA1) unit to
a restraining tactile stimulus as a function of
the rat's spatial orientation. The arrows and
associated letters mark the positions at which
the animal was restrained as it was pushed or
coaxed in a counter-clockwise direction around
the test platform. The firing rate of the unit
during tiffs procedure is illustrated by the
continuous frequency histogram in the middle of
the figure. The letters correspond to the
positions and the lines indicate the periods when
the rat was restrained. In between these periods,
the rat sat immobile in the same position for a
few seconds and then was moved on to the next
position. The bottom two lines show the raw data
taken at the onset of the unit response at A (1)
and during the absence of a response at D (2).
Time calibration for these data is 400 msec.
32
Preliminary evidence
33
A process of elimination Place units in the
hippocampus respond to an animals location
within the environment, not to a specific sensory
stimulus, motor behavior or motivational
incentive.
34
A Demonstration of Place Cell Firing
35
Central drug infusions
Intracerebro- ventricular (i.c.v.)
Infusion of a drug into the ventricles. This
method is used when direct delivery to the brain
is desired, limiting systemic effects.
Intracerebral (i.c.)
Infusion of a drug directly into a brain region
of interest. For example, an anesthetic like
lidocaine may be infused to produce a temporary
lesion or an antagonist can be used to block
specific receptors.