Task 4
Explain different techniques to measure the brain
Evaluating the Behavioral Effects of Brain Damage
Researchers destroy, disable, or inactivate specific brain regions to
observe resulting behavioral changes. By comparing the behavior of
animals with lesions to control animals, investigators infer what functions
the damaged region normally performs. This method helps map brain–
behavior relationships, but conclusions must be made carefully because
multiple brain areas contribute to any behavior.
Producing Brain Lesions
Brain lesion = damage to the brain
Different techniques can create permanent or temporary lesions:
Radio-frequency lesions: electrical current destroys all nearby tissue
non-selectively (through an electrode) (used to induce brain lesions
of subcortical regions)
Excitotoxic lesions: an excitatory amino acid (e.g., kainic acid) kills
cell bodies but spares passing axons (through a canulla).
Saporin–antibody conjugates: extremely selective toxin-based
lesions that kill only neurons expressing a particular receptor.
Local anesthetics or inhibitory drugs: produce temporary, reversible
lesions so the animal can act as its own control.
When do you use each brain imaging technique?
Invasive techniques
Stereotaxic techniques
Stereotaxic techniques allow precise placement of electrodes, cannulas, or
lesion-making tools deep within the brain.
Steps include:
1. Use a stereotaxic atlas to identify coordinates.
2. Place anesthetized animal in a stereotaxic apparatus.
3. Make a scalp incision, drill a hole, and lower the cannula/electrode to
the correct depth.
4. Produce lesion, implant device, or inject substance.
5. Close incision and allow recovery.
This method is also used in humans (e.g., deep brain stimulation: a
surgical procedure that involves implanting electrodes in the brain to
send electrical impulses to targeted areas, fetal cell implants).
,Histological methods
Histological methods are used to slice, stain, and examine the brain after
an experiment to verify that the lesion or implant is exactly where the
researcher intended.
1. Perfusion: blood is removed and replaced with fixative solution.
2. Fixation: brain is preserved to halt decay.
3. Slicing: using a microtome or cryostat to make thin sections.
4. Staining: applying dyes or antibodies to visualize cell bodies, fibers,
proteins, or intracellular structures.
5. Microscopy: light, electron, or confocal microscopes are used depending
on the needed level of detail.
Histology provides the anatomical confirmation required to interpret
behavioral results correctly.
Tracers
, Tracing Neural Connections: Researchers identify the inputs and outputs of
specific brain regions (to see which brain regions work together to create
specific behaviors) Two major classes:
Anterograde tracing (efferent axons)
Chemical (e.g., PHA-L) is injected into a region.
It is taken up by cell bodies and transported to terminals.
After staining, researchers see where neurons send their signals.
Retrograde tracing (afferent axons)
Chemical (e.g., fluorogold) injected into the target region.
Taken up by terminal buttons and transported back to cell bodies.
Reveals which neurons project into the region.
Metabolic (functional methods)
Researchers measure metabolic (metabolism) activity and gene activation
to identify which brain areas were active during a task.
Explain different techniques to measure the brain
Evaluating the Behavioral Effects of Brain Damage
Researchers destroy, disable, or inactivate specific brain regions to
observe resulting behavioral changes. By comparing the behavior of
animals with lesions to control animals, investigators infer what functions
the damaged region normally performs. This method helps map brain–
behavior relationships, but conclusions must be made carefully because
multiple brain areas contribute to any behavior.
Producing Brain Lesions
Brain lesion = damage to the brain
Different techniques can create permanent or temporary lesions:
Radio-frequency lesions: electrical current destroys all nearby tissue
non-selectively (through an electrode) (used to induce brain lesions
of subcortical regions)
Excitotoxic lesions: an excitatory amino acid (e.g., kainic acid) kills
cell bodies but spares passing axons (through a canulla).
Saporin–antibody conjugates: extremely selective toxin-based
lesions that kill only neurons expressing a particular receptor.
Local anesthetics or inhibitory drugs: produce temporary, reversible
lesions so the animal can act as its own control.
When do you use each brain imaging technique?
Invasive techniques
Stereotaxic techniques
Stereotaxic techniques allow precise placement of electrodes, cannulas, or
lesion-making tools deep within the brain.
Steps include:
1. Use a stereotaxic atlas to identify coordinates.
2. Place anesthetized animal in a stereotaxic apparatus.
3. Make a scalp incision, drill a hole, and lower the cannula/electrode to
the correct depth.
4. Produce lesion, implant device, or inject substance.
5. Close incision and allow recovery.
This method is also used in humans (e.g., deep brain stimulation: a
surgical procedure that involves implanting electrodes in the brain to
send electrical impulses to targeted areas, fetal cell implants).
,Histological methods
Histological methods are used to slice, stain, and examine the brain after
an experiment to verify that the lesion or implant is exactly where the
researcher intended.
1. Perfusion: blood is removed and replaced with fixative solution.
2. Fixation: brain is preserved to halt decay.
3. Slicing: using a microtome or cryostat to make thin sections.
4. Staining: applying dyes or antibodies to visualize cell bodies, fibers,
proteins, or intracellular structures.
5. Microscopy: light, electron, or confocal microscopes are used depending
on the needed level of detail.
Histology provides the anatomical confirmation required to interpret
behavioral results correctly.
Tracers
, Tracing Neural Connections: Researchers identify the inputs and outputs of
specific brain regions (to see which brain regions work together to create
specific behaviors) Two major classes:
Anterograde tracing (efferent axons)
Chemical (e.g., PHA-L) is injected into a region.
It is taken up by cell bodies and transported to terminals.
After staining, researchers see where neurons send their signals.
Retrograde tracing (afferent axons)
Chemical (e.g., fluorogold) injected into the target region.
Taken up by terminal buttons and transported back to cell bodies.
Reveals which neurons project into the region.
Metabolic (functional methods)
Researchers measure metabolic (metabolism) activity and gene activation
to identify which brain areas were active during a task.
