Module 6 - Biopsychology Methods

scientific method Ideas:

based on prior research, observations, and curiosity

scientific method Hypothesis:

• a prediction about an outcome (often written as an if–then statement)

  • Must be falsifiable → meaning it can be proven wrong with evidence

scientific method Observation stage:

collect data (experiments, case studies, archival data, etc.)

scientific method Conclusions:

analyze data using statistics and interpret results

scientific method Repeat cycle:

science is self-correcting; findings are refined over time

What is the logic of studying brain damage?

If damage to a specific brain area causes a specific deficit → that area is involved in that function

Why are Double Dissociation used?

to prove that a brain area controls a behavior and to rule out alternative explanations

Dissociation #1 (Area specificity)

○ Damage to one area impairs a behavior

○ Damage to a different area does NOT impair that same behavior

○ Example: Damage to the occipital lobe impairs vision, but damage to the auditory cortex does not

Dissociation #2 (Behavior specificity)

○ Damage affects one specific behavior, not all behaviors

○ Example: Occipital damage impairs vision but does NOT affect memory, hearing, or touch

Semantic memory + location

memory for facts and general knowledge - Left anterior temporal cortex

Episodic memory + location

memory for personal experiences and events - Hippocampus

What if you want to establish that an area controls a behavior?

You must demonstrate a double dissociation

How do scientists induce controlled damage

lesions/ablations

What are the advantages to lesions/ablations

• Allows researchers to target specific brain areas precisely

• Provides high control over variables (species, timing, genetics, extent of damage)

What are the disadvantages to lesions/ablations

Used only in animal research (ethical limitations)

Behavior changes may be caused by confounds

Diaschisis

temporary disruption in activity of undamaged brain regions (often due to swelling)

What are the Three Permanent lesions

Mechanical, Electrical, and Chemical lesions

What are the Three Temporary lesions

Hypothermia, Drug-induced lesions, Virtual lesions

Mechanical lesions

physically remove or destroy tissue (e.g., aspiration using suction)

Electrical lesions

pass electrical current through an electrode to destroy neurons

Chemical lesions

inject neurotoxic substances that selectively kill neurons

Hypothermia

cooling a brain area to temporarily disrupt its function

Drug-induced lesions

substances like sodium amobarbital temporarily inactivate brain regions

Virtual lesions

non-invasive techniques like TMS or tDCS

How do scientists create precise brain damage?

Through neuroanatomical atlas and stereotaxic apparatus

What is a stereotaxic apparatus?

• A device that holds the animal’s head in a fixed position

• Allows researchers to accurately guide instruments to exact brain locations

What is a neuroanatomical atlas?

• A detailed map of the brain that provides coordinates for specific regions

• Coordinates are often referenced relative to bregma (a skull landmark where sutures meet)

How are lesioned areas verified?

Histology

How is the brain removed and hardened (Histology)?

• Animal is given a lethal dose of anesthetic

• Brain is perfused with formalin, which preserves and hardens tissue

What is a microtome?

A device that slices the brain into extremely thin sections (micrometers thick) for microscopic analysis

What are neural stains? Why are they needed?

Neurons are naturally transparent → stains are used to make structures visible under a microscope

Golgi stain

stains the entire neuron, including dendrites and axons

Nissl (cresyl violet) stain

stains cell bodies (somas), allowing visualization of neuron density

Weigert-Weil stain

stains axons, especially myelinated fibers, making pathways visible

Meningiomas

• Grow between the meninges (protective layers of the brain)

• Affect the brain by applying pressure

• Usually benign → can often be surgically removed and do not spread

Infiltrating tumors

• Grow diffusely through brain tissue

• Usually malignant (cancerous)

• Treatments:

  • Surgery

  • Radiation therapy → uses high-energy waves to kill cancer cells

  • Chemotherapy → uses drugs that target and destroy rapidly dividing cells

• Tumors in critical areas (e.g., brainstem) are often difficult or impossible to remove

What are cerebrovascular disorders (strokes)?

Disorders involving blood flow disruption to the brain

Intracerebral hemorrhage

• A blood vessel ruptures and bleeds into brain tissue

• Causes damage by:

  • Depriving neurons of oxygen and glucose

  • Blood toxicity damaging surrounding tissue

• Treatment often involves surgery

Cerebral ischemia

○ A blood clot blocks an artery

○ Prevents oxygen and glucose from reaching neurons

○ Treatment includes clot-dissolving drugs or surgery

Aneurysm

• Weakening and ballooning of a blood vessel wall

• Can rupture and cause hemorrhage

• Treated using procedures like the Guglielmi detachable coil, which blocks the aneurysm

Contusion

More severe brain injury involving bruising of brain tissue that can lead to permanent damage

Encephalitis

Inflammation of the brain typically caused by infections

Bacterial infections (brain)

Infections such as meningitis (infection of protective membranes) and syphilis (can remain dormant and later damage the brain)

Viral infections (brain)

Infections caused by viruses such as neurotropic and pantropic viruses

Neurotropic viruses

Viruses that specifically target the nervous system (e.g., rabies, West Nile virus)

Pantropic viruses

Viruses that affect multiple body systems, including the nervous system (e.g., mumps)

Neurotoxins

Substances that damage or destroy neurons

Heavy metals

Neurotoxins such as lead and mercury that impair brain development and function

MPTP

A neurotoxin converted in the brain to MPP+ that selectively destroys dopamine neurons

PCBs (polychlorinated biphenyls)

Environmental toxins linked to cognitive deficits when exposure occurs during development

Virtual lesion

A temporary disruption of normal brain function without physical damage

Transcranial Magnetic Stimulation (TMS)

A non-invasive technique using magnetic pulses to temporarily disrupt brain activity

Single-pulse TMS

TMS method delivering one pulse, generally considered safe

Repetitive TMS (rTMS)

TMS method delivering repeated pulses; higher frequencies increase seizure risk

TMS strengths

Provides evidence a brain region is necessary for behavior and supports imaging studies

TMS weaknesses

Limited precision, possible side effects, seizure risk (rare), mechanisms not fully understood

Transcranial Direct Current Stimulation (tDCS)

A non-invasive method using weak electrical current to alter brain activity

Cathodal stimulation

Negative electrode that decreases neuronal activity (inhibitory effect)

Anodal stimulation

Positive electrode that increases neuronal excitability

tDCS effects

Subtle changes in brain activity that are still being researched

Microelectrode recording logic

Increased neuron firing during a behavior suggests involvement in that behavior

Microelectrode recording method

Involves inserting an electrode into the brain to record real-time activity of single neurons

Microelectrode recording strengths

Extremely high precision, can record from single neurons

Microelectrode recording weaknesses

Records only a small number of neurons and lacks large-scale brain activity

Microelectrode stimulation logic

Stimulating neurons should produce or alter behavior, showing causation

Microelectrode stimulation method

Applying electrical current through an implanted electrode to activate neurons

Microelectrode stimulation strength

Demonstrates causal relationships

Microelectrode stimulation weakness

Artificial stimulation may not reflect natural brain activity

tDCS vs microelectrodes

tDCS is non-invasive and less precise, while microelectrodes are invasive and highly precise

Spatial resolution

How precisely a technique can locate brain activity

Temporal resolution

How accurately a technique tracks changes in brain activity over time

Averaging

A method that reduces noise by combining repeated trials to improve signal reliability

Event-related designs

Experimental designs that isolate brain responses to specific stimuli or actions

Subtraction method

A technique comparing task and baseline conditions to isolate specific brain activity

Task condition

Experimental condition that includes the behavior of interest

Baseline condition

Condition that includes everything except the target behavior

Imaging environment effects

fMRI environment can impair memory, attention, and performance due to noise, confined space, and unnatural setting

Ecological validity

The extent to which behavior in a lab reflects real-life behavior; often low in imaging studies

Subtraction logic (imaging)

Compares task condition and control (baseline) condition to isolate brain regions responsible for a function

Task condition

Experimental condition that includes the behavior of interest

Control (baseline) condition

Condition that includes everything except the target behavior

Interpretation issue (brain activity)

Brain activity does not imply causation or necessity for a behavior

CT scan (CAT)

Imaging technique using X-rays to create structural brain images

CT scan mechanism

Uses X-rays passing through the head; different tissues absorb different amounts and a computer reconstructs a 3D image

CT scan uses

Commonly used for head injuries, bleeding, and tumors

CT scan strengths

First noninvasive imaging method and still useful clinically

CT scan weaknesses

Only structural information and poor spatial resolution (~0.5–1 cm)

PET scan

Functional imaging technique using radioactive tracers to measure brain activity

PET scan tracers

Substances like glucose, water (O-15), or gases used to track brain activity

PET scan mechanism

Tracer decays emit positrons that collide with electrons, producing gamma rays detected to map brain activity

Regional cerebral blood flow (rCBF)

Measure of blood flow used in PET; more blood flow indicates more activity

Hemodynamic technique

A method that measures blood flow as an indirect indicator of neural activity

PET indirect measurement

PET measures blood flow, not neurons directly

PET strengths

First functional imaging technique with decent spatial and temporal resolution

PET weaknesses

Expensive, poor temporal resolution (~1–1.5 sec), and requires block designs

fMRI

Functional imaging technique measuring brain activity using magnetic fields and blood oxygen levels

MRI vs fMRI

MRI measures structure while fMRI measures brain function/activity