Assessing Brain Methods

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Methods for Cellular Anatomy

Nissl and Golgi staining

Assessing Gross Anatomy

Computerized Tomography (CT), Magnetic Resonance Imaging (MRI), and Diffusion Tensor Imaging (DTI)

CT Scan

Static 3D imaging made from multiple X-ray beams. Based on tissue density. White areas are bone; dark areas are fluid.
Advantages: Non-invasive, accessible, fast for diagnosis, widely available.
Disadvantages: Shows only structure, radiation exposure, doesn’t differentiate white or gray matter, moderate spatial res (~1mm)

MRI Scan

Static 3D imaging made from radio frequencies and magnetic fields. Resolution depends on the magnetic field.
Advantages: Higher resolution than CT, non-invasive, no radiation, good spatial resolution.
Disadvantages: Expensive, extensive setup, limited movement, bad temporal resolution.

DTI Scan

Type of MRI imaging that shows neural tracts (diffusion of water tissue)
Advantages: Good for networks and degeneration of axons, same as MRI.
Disadvantages: Can’t show directionality, same as MRI.

Assessing Function

Positron electron tomography (PET), Functional Magnetic Resonance Imaging (fMRI), Electroencephalography (EEG), and Transcranial magnetic stimulation (TMS)

PET Scan

Dynamic 3D images made from biochemical activity. Radioactive molecules that have particles detected by camera. Uses multiple trials (subtractive analysis). Measures blood flow change/chemistry, inferring neural activity. (Types of tracers; glucose = glucose metabolism, amyloid = alzheimer’s, dopamine = parkinsons/SAD)
Advantages: Can see changes in biochemical activity. Can choose many different radiochemicals to track different things
Disadvantages: invasive, not a direct measure of neuronal activity, poor temporal and spatial res, expensive, can’t specify location?

fMRI Scan

Static AND dynamic 3D images made from blood oxygenation levels (oxyhemoglobin is higher after neural activation). Discovered the default mode network.
Advantages: Noninvasive. Repeatable. Good spatial res. No averaging required. Can display BOLD

Disadvantages: Expensive, extensive, limited movement, can be uncomfortable, poor temporal res., a little subjective

EEG Scan

Electrodes attached to the skull. Measures thousands of graded potentials. Show states of consciousness or abnormal activity patterns (in sleep studies, anesthesia, epilepsy). ERP: brief change in EEG signal in response to stimulus; used to localize activity associated with particular sensory event
Advantages: Simple, noninvasive, inexpensive, repeatable. Free movement. Good temporal res

Disadvantages: limited precision. Limited spatial res. Limited to scalp.

TMS Scan

Dynamic 3D images based on magnetic fields from a wire attached to the head. Can disrupt behaviour and cause temporary lesions. Lesions allow comparison between stimulated and non-stimulated conditions.

Advantages: Non-invasive, simple, inexpensive. Provides info on functional activity or findings from lesion method.

Disadvantages: Can’t do people with brain injury, limited precision, doesn’t allow localization of effects