Functional Neuroanatomy

What is neuroanatomy?

the study of the brain/behavior relationship

What do clinical neuropsychologists focus on?

• clinical neuropsychologists focus on the impact of BOTH NORMAL and ABNORMAL brain functioning (on cognition, emotion, and behavior)

• data is collected from several sources:

  • standardized testing

  • behavioral observations

  • collateral information (info collected from sources OTHER THAN the patient to provide a fuller idea or picture of what is going on)

What is functional neuroanatomy?

A description of the central and peripheral nervous system that focuses on BEHAVIOR that correlates, or is associated with, SPECIFIC neuronal structures OR systems (the way these structures are connected)

In what way do individuals living with acquired brain disorders provide INSTRUMENTAL evidence of why we have to consider neuroanatomical structure AS WELL AS the function of these structures?

People with acquired brain injuries, like stroke, TBIs/traumatic brain injuries, tumors, etc.) often show deficits that don’t match up to a “clean textbook picture” of what a damaged structure SHOULD do, or how this disease SHOULD manifest.

• someone with damage in the frontal lobe might not ONLY show poor planning (a part of executive functioning), but ALSO memory issues. This is because the frontal lobe communicates with the hippocampus/SELECTIVELY retrieves relevant or important memories from it

• so, damage to ONE area of the brain can ALSO impact circuitry or a network (a system) that goes BEYOND what those specific structures are traditionally known for

IMAGING: What is a CT (computed tomography) scan? Is it used for clinical applications (patients) or within research (research subjects)?

Uses X-rays to create cross-sectional images of the brain that are DETAILED (brain, skull, sinuses, even eye sockets)

Pro: quick, so often one of the first scans or imaging techniques used in the emergency room (to detect strokes or head trauma) —> as soon as a person comes in, think CT scan!!!!

Con: not highly sensitive (good for gross anatomy, not so good for small or subtle details), and exposes people to radiation (via the X-ray), even if it is non-invasive

IMAGING: What is a MRI (magnetic resonance imaging) scan? Is it used for clinical applications (patients) or within research (research subjects)?

Uses a large magnet, radio waves, and a computer to create DETAILED images of the brain’s structures.

Pros: No radiation needed (safer than CT scans for repeated imaging)

• high soft tissue contrast (contrast between the gray matter, or neurons, and white matter, or axons)

• if you change sequences (T1-weighted, T2-weighted, T3-weighted), you can highlight DIFFERENT tissue properties —> this makes MRI scans extremely versatile + applicable to clinical settings

• we can even capture subtle lesions with MRI scans!! also useful for tumors and multiple sclerosis (where the myelin sheath of axons, an insulator, is attacked - people with MS have “leaky” axons where transmission is disrupted or takes longer as a result)

Cons: People with irremovable metal in the body (like pacemakers or prosthetic limbs) can’t really use this test….

What are the differences between T1, T2, and FLAIR sequences for MRI scans?

T1 weighted: fat appears bright, fluid (CSF) appears dark, and white matter looks gray.

• helps see the overall structure of the brain

T2 weighted: the opposite - fat appears dark, CSF/fluid appears light

• helps identify brain lesions that contain a LOT of water, or fluids

FLAIR: a special version or sequence of T2

• this is where “normal” CSF, such as any found in the ventricles or sulci (grooves or folds of the brain), is DARK or suppressed.

  • this allows us to easily see CSF abnormalities (ex. brain lesions) without “caring” about any normal places where we expect to see high volumes of fluid, such as ventricles

IMAGING: What is a fMRI (magnetic resonance imaging) scan? Is it used for clinical applications (patients) or within research (research subjects)?

fMRI scans measure brain activity by detecting changes in BLOOD FLOW (think f as in ferritin/IRON) —> blood oxygenation helps us tell what neurons are active

fMRI scans are not often used in clinical settings (more in a research context).

By tracking and comparing brain activity to what the patient was doing at the time, the fMRI can help “map” brain activity

• basically, during the scan, the patient can do a task

• the fMRI will show us (via measuring changes in blood oxygenation) which SECTIONS OF THE BRAIN were most active while the patient was doing the task

• however, fMRIs aren’t that fast. GREAT spatial resolution (identifying and isolating active brain structures), NOT SO GREAT temporal resolution (blood oxygenation changes are slower than action potentials)

• fMRIs are also expensive, and mostly used in research (NOT clinical!)

IMAGING: What is a PET (positron emission topography) scan? Is it used for clinical applications (patients) or within research (research subjects)?

This imaging technique uses radiotracers to create 3D images. These radioactive tracers bind chemically to compounds of interest, like glucose and dopamine.

Pros: PET scans are really good for letting us see what is going on (neuro)chemically or metabolically. Works in both clinical or research contexts, but it’s specialized clinical (ex. for disorders that are neurotransmitter-deficiency based, like Parkinson’s, and involve excitotoxicity like Alzheimer’s) and mostly used in research to study neurotransmitters.

Cons: Not great for seeing precise anatomy/structural detail, LOW temporal resolution (not great for detecting quick changes). Also, this is invasive because of the radioactive tracers: so we get exposed to radiation AND the tracers are inside the brain.

IMAGING: What is an angiogram? Is it used for clinical applications (patients) or within research (research subjects)?

Angiograms use X-rays (immediate con because this implies exposure to radiation) and a special dye to examine blood flow + blood vessels in the brain. So this is also invasive.

• imaging blood flow via angiograms can tell us about blockages (ex. what happens in strokes, where that triggers the neural excitotoxicity that strokes are known for)

• can also detect other vascular (=to do with the veins AND arteries) abnormalities

• detects aneurysms (which leads to blood vessels ballooning and possibly rupturing)

These are primarily clinical, and used for patients instead of research subjects.

IMAGING: What is a DTI (diffusion tensor imaging) scan? Is it used for clinical applications (patients) or within research (research subjects)?

DTI measures the direction and speed at which water molecules move between cells.

—> this helps us create COLOR-CODED images that show the orientation/appearance of white matter fibers

So this helps us look at axonal disruptions or damage, and examine the brain’s connectivity. Great for helping us look at TBIs or strokes BUT are expensive so are not used very much in clinical contexts (more for research)

IMAGING: What is an EEG (electroencephalogram)? Is it used for clinical applications (patients) or within research (research subjects)?

Measures the electrical activity of the brain (very widely used in research contexts)

• high temporal resolution (can detect very quick changes in the electrical activity of the brain)

• non-invasive and kind of inexpensive

BUT they have poor spatial resolution (very hard to isolate or identify the activity of certain brain structures relative to other brain structures)

• it’s mostly good for surface level activity, because EEGs can’t really penetrate to “inside” the brain (signals from deeper brain structures are weaker + harder to isolate thanks to the relatively poorer spatial resolution)

Can be used in both a clinical (for epilepsy and sleep disorders) and research context (ex. to detect brain rhythms).