Week 3 B

Behavioral Neuroscience Research methods

  • correlation tests: relation, ex. to see if a certain neurons activity is correlated with the behavior

    • ex. touching a crayfish which causes a depolarization of the LGI neuron leads to a tail reflex

      • We can say that the LGI activity is correlated with the tail flick; involved in the tail flick behavior

  • necessity: to see if the activity of neurons is necessary to cause activity even when the cell is not acitivated

    • dam

    • ex. We hyperpolarized the LGI neuron and it cant fired the action potential, if we touch the crayfish there is no tail flex

      • We can then say that the acitivty of the LGI is necessary to cause the behavior

  • Sufficiency: to see if the activity of neurons are sufficient enough to cause behavior

    • if the behavior occurs when the neurons are stimulated even when not though possible

    • ex. We cause an action potential to the LGI neuron artificially to see if we can cause the tail flick

      • Passes the test since when activity there is a tail flick

Classic Methods

Old Way: Brain Lesions → Tests for Correlation

  • damage to neural tissue (stereotaxic surgery) → using heat or electricity

  • Traumatic Injury

    • Stroke, removal of tissue

  • Goal: if a certain part of the brain was responsible for a behavior then damage will impair that function

    • Damage to the same part of the brain across patients leading to the same impairment show connection to function

Pharmacology → Tests for Sufficiency

  • Use of lidocaine and glutamate agonists

  • The inactivation → Tests for necessity

    • Using GABA and Lidocaine

  • The Activation → tests for sufficiency

    • Glutamate Agonists

Other Sufficiency

  • Electrical Stimulation to activate nearby cells

Other Correlation Examples

  • Testing with electrodes and brain imaging to see what regions are active when the behavior occurs

    • electrodes record the action potentials but only indirect measures of activity

Limitations

  • A single brain region will have a big diversity of different cell types which makes the older methods insufficient

  • There is no specificity to these methods since they will always effect more than one of the cells that are being studied

  • Solution: The use of modern methods

Optogenetics

optogenetics

  • Discovered through the opsin in algae in bacteria

  • Uses genetic tools to insert light sensitive ion channels into neurons

  • use lasers to inactivate/activiate neurons in the brain

  • Channelrhodopsin → responds to blue light and allows for Na+ ions to depolarize

  • Halorhodopsin → responds to yellow light and allows for Cl- ions to hyperpolarize

Six Steps to Optogenetics → adding the channels into mammals to study them

  1. Make a genetic sequence for the encoded gene and a promoter sequence which will be for a specific gene

  2. We insert the genetic sequence into a virus

  3. injection of the virus into the brain region of interest; Virus infects the specific cells and creates channelrhodopsin/halorhodopsin in them

  4. Implant a fiberoptic cable connect to a light source into the specific brain region

  5. The light will either open or close the channels

  6. We can record the activity of the cells to see how they cause specific behaviors

Example:

  • The rat had a virus inserted into the VAG region which is response for the freezing response in them when they’re in danger

  • The promoters for the channelrhodposion was glutamatergic and when the blue light shone through the fiber-optic then we can see that the freezing response had been initiated

Chemogenetics *

  • Using engineered receptors (DREADDs) to activate or inhibit

    • Dreadd receptors are derived from acetylcholine receptors to now bind the clozapine-N-Oxide

    • DREADD: Desiner Receptor Exclusively Activated by Designer Drugs

    • Use the system to target genes of interest

  • Uses Clozapine N Oxide

  • We will also use a virus and promoter sequence to insert these modified receptors

  • We can just inject the virus into the specific brain region

    • We will then inject clozapine-N-oxide to the bloodstream to express the receptor that can be excitatory or inhibitory

    • When active the channel will activate a g protein cascade which leads to the opening of a specific channel

      • Excitation: HM3Dq Receptor

      • Inhibition: HM3Di Receptor

example: Inhibiting Pain with Dredds

  • neurons in the PAG that control pain

    • clozapine-n-oxide caues no action potentinal and leads to no pain perception

Selectivity

  • both dredd receptors and optogenetics target specific proteing and specific regions of the brain

  • can target specific regions of the brain by using a promoter of a specific neuron and the virus sequence

  • help us control only a specific function by targetting a specific group of cells

Calcium Imaging

  • records specific neuron types in a given brain area

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Correlating Brain Activity to Behavior

Comparison of Neccessity and Sufficiency Methods

  • Brain Lesions → destroying parts of the brain

    • con: permanent, no cell type specificity

  • Intracranial Drug Infusions → temporarily inactivates neurons in the brain with the use of a drug

    • temporary and slow,no cell type specificity

  • electrode stimulation → disruption of neurons through electircal currecent

    • pros: is temporary and fast,no cell type specificity

  • Chemogentics (DREADDS) → genetically engineers a designer drugs to be injected into the body

    • selective, temporary, and slow

  • Optogenetic → the use of a laser light connected to a fiber-optic to target neurons

    • temporary, fast, selective, you need to implant the fiber-optic in the brain of the organism which is invasive and permanent

Neural Recordings in Humans

EEG (Electroencephalography)

  • Putting electrode beads on the skin of the skull

  • Records combined neural activity in an entire brain region

    • ex. hearing a crowd making noise but being unable to hear individual screams

  • Pros: noninvasive, accurately classifies brain states (awake or sleeping), diagnosing, fast

  • Cons: unable to record individual action potentials

PET (Positron Emission Tomography) Scan

  • Radioactive ligands (glucose) are injected into the bloodstream

  • The scanner will detect the concentration of the radioactive ligands in the brain while individuals are doing a task to see what parts are active

  • We can contrast the concentrations between patients

  • Pros: provides infomration regardinthe whoel brain

  • Cons: injection is invasive

Other Tests

  • fMRI: (expensive) noninvasive test which provides high spatial resolution and we could tell where each signal comes from but is also slow to detect which brain regions are active during certain tasks

    • Detect the tissues that are consuming the most oxygen

  • In Vivo Recording: recording invdividual cells with electrodes in the brain but does not provide entire brain activity

  • electrodes: (cheap) recording lots of indivudal neurons in a brain region but we can only record that specific brain region and is fast

Other Methods of Studying Anatomy/Structure

CAT/CT Scan

  • Computerized Axial tomography Scanning: produces a series of x rays from different angles from the planes to brain a 3D image

    • involves radiation

MRI → Noninvasive

  • Magetic resonance imaging: produces information on what brain regions are active baased on blood oxygenation levels

    • provides anatomical brain information

  • Works by measuring the radiofrequency waves emitted by H atoms when exposed to a magnetic field

  • Measures shapes and sizes of brain regions across individuals

  • Gives us information of anatomy changes due to degneration and location of damgetion to see that damage is associated with a behavior

Ex Vivo (previously living tissues) Analyses in extracted brain tissues

Anatomical Staining:

  • To detect specific proteins in a tissue

  • Process: Using antibodies that will bind to those proteins and then make a treatment that will make those antibodies flourescent

  • You can overlap the stains to see what proteins are in specific cells in a brain region

  • Characterizies which proteins are found in specific regions in the brain

In Situ Hybridization

  • Using a radioactive probe to detect neurons with a specific RNA/DNA to see where the gene is activated

  • see where certain mRNA is being produce in certain brain regions

  • to see where and when a certain gene is being expressed

  • see the activated genes in a neuron

  • allows to see which neurons are activated in specific brain regions

Things to Consider

  • INvasiveness

  • experimental or correlation

  • in vivo (living) or ex vivo (extracted tissue)