Brain Structure and Function: Research Methods

Posted on Jan 17, 2025 in Biology

Brain Structure and Function

Olfactory/gustatory systems do not have contralateral organization.
The primary motor cortex controls the contralateral side of the body.
Left hemisphere: Speech and comprehension.
Right hemisphere: Non-verbal spatial abilities.
Lateralization: Functional differences between hemispheres.
Corpus callosum: Connects hemispheres.
Basal ganglia: Includes the caudate nucleus, putamen (striatum), and globus pallidus.
Lesions to this area result in uncontrolled movements (e.g., Parkinson’s and Huntington’s disease).

The limbic system plays a role in emotions and memory formation.

Nuclei include:

Thalamus: Relays sensory information from the brainstem to the forebrain/cortex.
Hypothalamus: Controls the endocrine and autonomic nervous systems (controls fighting, fleeing, feeding, and mating).
Pituitary: Connected to the hypothalamus, the “master gland”, controls the endocrine system of the body.

Metencephalon:
- Cerebellum (little brain, motor coordination)
- Pons (has fibers that are relayed from the forebrain to the cerebellum)
Myelencephalon:
- Medulla oblongata (base of the brainstem; many nuclei that are vital for breathing and cardiovascular function)

Experimental Ablation: Removing or destroying tissue of a lab animal to observe behavior; the oldest method; lesion studies.
Radiofrequency lesion: Passing an alternating current through a wire electrode; heat kills cell bodies and axons.
Excitotoxic lesions: Injecting a chemical through a cannula, applying a glutamate receptor agonist (kainic acid); stimulates neurons to death, kills cell bodies, not axons.
Reversible lesion: Temporary disruption, injecting muscimol through a cannula; blocks action potentials by stimulating GABA receptors.
Sham group: Animals have surgery that inserts an electrode or cannula, but no current or chemical is injected; controls for incidental damage.

Bregma: Junction of sagittal and coronal bones of the skull, anterior fontanelle during infancy, closes in the first 36 months of life in humans (soft spot); reference point.

Goal: Visualize tissue as it was when the organism was alive.

Place the brain in a fixative (formalin), which prevents decay, preserves tissue close to its natural state, and prepares tissue to be processed.
Cut into thin sections (10-80µm thick) 0.001 mm.
Immunohistochemistry: Antibodies bind to antigens in tissue; antibodies are made by injecting a protein of interest and isolating antibodies from serum; tissue is incubated.
CT Scan: Computerized tomography, the oldest method, passing X-ray beams through the head; blood absorbs a lot of radiation and looks white.
MRI Scan: Magnetic resonance imaging, higher resolution than CT Scan, no X-rays, passing a strong magnetic field through the head and radio waves.
Diffusion Tensor Imaging: Modification of MRI, based on information about the movement of water molecules; visualize bundles of axons.

Single-unit: Implant microelectrodes, record the activity of individual neurons; the location of electrodes can be moved.
Multi-unit: Implant macroelectrodes, record postsynaptic potentials of thousands of cells in one location; EEG-like hum.
Immediate Early Gene Expression: Turn on when neurons are active, can be behaviorally induced or directly through current; common IEGs are Fos and Arc.

Positron Emission Tomography (PET): The first functional imaging method, involved the administration of a radioactive tracer (2-deoxyglucose); the tracer is taken up by active cells and emits a signal (positron); very expensive, poor spatial and temporal resolution.
- Increased uptake of 2-deoxyglucose in areas involved in movement.
- Indicates an increased metabolic rate in these regions.
Functional MRI (fMRI): Best spatial and temporal resolution, detects levels of oxygen in the brain’s blood vessels.
- BOLD signal: Blood oxygen level-dependent.

Mutated genes can be produced in the laboratory and inserted into the chromosomes of mice.

Constitutive Knockout Mice: The target of the mutation prevents the production of a certain protein.
- Limitations: Compensatory mechanisms.
Conditional Knockout Mice: Temporal controls over the genes.
- Advantage: Mice can develop normally.