competition restated fmri lesson : you should decide for yourself instead of blindly accepting what...

Competition restatedCompetition restatedfMRI Lesson : You should decide for yourself instead of blindly accepting what some authors claim

Which is more difficult?

Rocket science

Or

Brain Surgery

Stereotaxic surgery is the first step in many biopsychological experiments

The goal is to place an electrode or some other device at a specific target site in the brain.

This is a small animal (rat) This is a small animal (rat) stereotaxic apparatusstereotaxic apparatus ElectrodeElectrode

manipulatormanipulator

ElectrodeElectrodeHolderHolder

Ear barsEar bars

Incisor barIncisor bar

““U” frameU” frameBase plateBase plate

Step 1: Consult the stereotaxic atlas for coordinates Step 1: Consult the stereotaxic atlas for coordinates of the brain area you are interested in.of the brain area you are interested in.

Stereotaxic AtlasStereotaxic Atlas

Step 1a: Find the plate that has the brain region of Step 1a: Find the plate that has the brain region of interest (e.g., the caudate-putamen, CPu).interest (e.g., the caudate-putamen, CPu).Note that this plate is a coronal section +0.70 mm Note that this plate is a coronal section +0.70 mm (anterior) to Bregma.(anterior) to Bregma.

CPu

Bregma is a landmark on Bregma is a landmark on the skull surface where the skull surface where the coronal suture meets the coronal suture meets the sagittal suture.the sagittal suture.

Coronal sutureCoronal suture Sagittal sutureSagittal suture Lambdoid Lambdoid suturesuture

Plane Medial CPu

AP 0.7 mm

ML 2.0 mm

DV 4.4 mm

Step 1b: Determine the coordinates of the point in Step 1b: Determine the coordinates of the point in the brain where the electrode tip is to be positioned.the brain where the electrode tip is to be positioned.

Suggestion – it is always a good idea to check the Suggestion – it is always a good idea to check the literature to see what coordinates others have used.literature to see what coordinates others have used.

AP (anterior-posterior)AP (anterior-posterior)ML (media-lateral)ML (media-lateral)DV (dorsal-ventral)DV (dorsal-ventral)

CPu

Step 2: Use an approved surgical protocol to Step 2: Use an approved surgical protocol to anesthetize the animal and prepare for surgery.anesthetize the animal and prepare for surgery.

Step 3: Mount the animal in the stereotaxic Step 3: Mount the animal in the stereotaxic apparatus by placing incisors over the incisor bar apparatus by placing incisors over the incisor bar and gently inserting the ear bars so that they enter and gently inserting the ear bars so that they enter the auditory canal and meatus.the auditory canal and meatus.

Step 4: Clean and incise the scalp exposing the Step 4: Clean and incise the scalp exposing the skull surface.skull surface.

Step 5: use the 3 dials on the stereotaxic Step 5: use the 3 dials on the stereotaxic manipulator to place the tip of the electrode at the manipulator to place the tip of the electrode at the Bregma.Bregma.

DV dialDV dial

ML dialML dial

AP dialAP dial

Step 6: Read the 3 vernier scales corresponding to Step 6: Read the 3 vernier scales corresponding to the AP, ML and DV dials.the AP, ML and DV dials.

DV dialDV dial

ML dialML dial

AP dialAP dial

Main Scale

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

How to read a Vernier scaleHow to read a Vernier scale

How to read a Vernier scaleHow to read a Vernier scale

Now lets read the ML coordinate.

Vernier Scale

ML = 10.2 mm

Main Scale

And now the DV coordinate.

DV = 23.7 mm

Vernier Scale

Main Scale

How to read a Vernier scaleHow to read a Vernier scale

Coordinates from Coordinates from the stereotaxic atlasthe stereotaxic atlas

Coordinates just read Coordinates just read from the stereotaxic from the stereotaxic manipulatormanipulator

23.7 mmDV

10. 2 mmML

31.5 mmAP

BregmaPlane

4.4 mmDV

2.0 mmML

0.7 mmAP

Medial CPu

Plane

++/-- 19.3 mmDV

11.2, 8.2 mm ML

32.2 mmAP

Medial CPuPlane

===

NEW CoordinatesNEW Coordinates

Step 7: Calculate the new coordinates within the Step 7: Calculate the new coordinates within the brain relative to the bregmabrain relative to the bregma

Step 8: Use the new coordinates to reposition the Step 8: Use the new coordinates to reposition the electrode. First, do the AP, then the ML on each electrode. First, do the AP, then the ML on each side marking each spot.side marking each spot.

DV dialDV dial

ML dialML dial

AP dialAP dial

AP = 32.2

ML = 11.2 ML = 8.2Step 9: Drill holes through the skull at each Step 9: Drill holes through the skull at each mark.mark.

Step 10: Now lower the electrode into the brain at Step 10: Now lower the electrode into the brain at the new DV coordinate.the new DV coordinate.

DV dialDV dial

ML dialML dial

AP dialAP dial

Step 11: Either pass current or inject chemical to Step 11: Either pass current or inject chemical to make a lesion. Repeat on other side of brain.make a lesion. Repeat on other side of brain.

Step 12: Suture wound and follow postoperative Step 12: Suture wound and follow postoperative care procedures. Surgery Complete!care procedures. Surgery Complete!

With all the rights and privileges hereto forth bestowed

This will open the door to many techniques including:This will open the door to many techniques including:

1)1)Lesion methodsLesion methods

2)2)Electrical stimulation and recordingElectrical stimulation and recording

3)3)Central drug infusionsCentral drug infusions

Lesion MethodsLesion Methods

Current is passed through an electrode to heat the exposed Current is passed through an electrode to heat the exposed tip and destroy adjacent tissue.tip and destroy adjacent tissue.

A B C

Electrolytic and radiofrequency currentElectrolytic and radiofrequency current

Electrolytic lesions of the CPu

Lesion MethodsLesion Methods

A chemical is infused through a cannula to selectively A chemical is infused through a cannula to selectively destroy cells and spare fibers of passage.destroy cells and spare fibers of passage.

Neurotoxin lesionsNeurotoxin lesions

Ibotenic acid lesion of hippocampus

Lesion MethodsLesion Methods

Cortical tissue is drawn off by suction through a Cortical tissue is drawn off by suction through a fine-tipped glass pipette.fine-tipped glass pipette.

Aspiration LesionAspiration Lesion

Aspiration lesion of amygdala and entorhinal cortex (monkey)

Lesion MethodsLesion MethodsKnife cutKnife cut Cutting a nerve or tract without Cutting a nerve or tract without

severely damaging surrounding severely damaging surrounding tissue.tissue.

8

7

6

54

3

1

2Knife cut of the perforant path input to the hippocampus

Lesion MethodsLesion MethodsCryogenic Cryogenic blockadeblockade

A method of temporary inactivation A method of temporary inactivation (reversible lesion). Coolant is pumped (reversible lesion). Coolant is pumped through a cryoprobe causing neurons near through a cryoprobe causing neurons near the tip stop firing. The temperature is the tip stop firing. The temperature is maintained above freezing so that there is maintained above freezing so that there is no structural damage.no structural damage.

Electrical stimulationElectrical stimulationBipolar Bipolar electrodeelectrode

Two insulated wires wound tightly together Two insulated wires wound tightly together are are used to deliver weak pulses of current used to deliver weak pulses of current to increase the firing of neurons near the to increase the firing of neurons near the tiptip. Electrical stimulation often elicits . Electrical stimulation often elicits behavioral responses such as eating, behavioral responses such as eating, drinking, sleeping, attacking and copulation. drinking, sleeping, attacking and copulation. The behavioral effects are usually opposite The behavioral effects are usually opposite to those produced by a lesion.to those produced by a lesion.

Electrical recordingElectrical recordingIntracellular Intracellular unit recordingunit recording

Used to study the electrophysiological Used to study the electrophysiological responses of a single neuronresponses of a single neuron. Records . Records graded graded fluctuations in the neuron’s membrane fluctuations in the neuron’s membrane potentialpotential. Usually performed on chemically . Usually performed on chemically immobilized animals because it is hard to keep immobilized animals because it is hard to keep the tip of a microelectrode positioned inside a the tip of a microelectrode positioned inside a neuron in a freely moving animal.neuron in a freely moving animal.

ExtracellularExtracellularunit recordingunit recording

Records the action potentials of a neuronRecords the action potentials of a neuron through a microelectrode whose tip is positioned in through a microelectrode whose tip is positioned in the extracellular fluid next to it. It provides no the extracellular fluid next to it. It provides no information on the neuron’s membrane potential.information on the neuron’s membrane potential.

Multiple unitMultiple unitrecordingrecording

Large electrodes are used to pick up Large electrodes are used to pick up signals from signals from many neuronsmany neurons, adding the total number of action , adding the total number of action potentials per unit of time.potentials per unit of time.

O’Keefe & Dostrovsky (1971)

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.

Preliminary evidence

A process of elimination… Place units in the hippocampus A process of elimination… Place units in the hippocampus respond to an animal’s location within the environment, not to a respond to an animal’s location within the environment, not to a specific sensory stimulus, motor behavior or motivational specific sensory stimulus, motor behavior or motivational incentive.incentive.

A Demonstration of Place Cell Firing

Central drug infusionsCentral drug infusionsIntracerebro-Intracerebro-ventricular ventricular (i.c.v.)(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.

IntracerebralIntracerebral (i.c.)(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.