Neuroscience Methodology
Fall 2002

Several problems make studying the nervous system difficult:

1) The nervous system of humans is very complex
2) Neurons are very small
3) Neural activity changes very quickly
4) The brain & spinal cord are protected by bone
Scientists have had to develop several techniques to see soft tissue. Advances in understanding the nervous system are closely associated with advances in technology.

Techniques to see brain structures

1) Surgery: A dangerous way to visualize the brain. Used only for medical treatment (remove tumor or epileptic focal point; implant stimulating electrode).

Stereotaxic surgery makes use of a metal device attached to the head to position things precisely in the brain (e.g., lesion or a tumor) 2) Computerized Axial Tomography (CAT scan): Take x-ray from many points around head. Problem is that the skull is dense. Computer looks at density from each x-ray and makes a map of the brain. Can enhance contrast by injecting dye into the blood stream. Pictures are a bit fuzzy.
 

3) Magnetic Resonance Imaging (MRI): can see soft tissue in amazing detail. The head is placed in a magnetic field which causes all the charged atoms to line up. Water which has 2 H atoms (H20) is especially sensitive. Disruption of field causes atoms to resonate releasing electromagnetic energy. This is a non-invasive way to see tumors, strokes, or other damage to brain tissue (Images of damaged brains).
 

4) Histology: Examination of microscopic structures in dead tissue. Need to stain the tissue to see things. Several types of stain:

Techniques to measure brain activity

Measuring brain activity requires overcoming two problems:

a) Temporal resolution (time)--linking stimuli to brain activity
b) Spatial resolution (location)--linking activity to brain region 1) Electroencephalogram (EEG): Use scalp electrodes to measure the electrical activity of groups of neurons. Great temporal resolution, but poor spatial resolution.
 

2) Positron-emission tomography (PET): Inject radioactively labeled glucose (or other compounds) into the blood. Brain needs a lot of energy to run so blood (and glucose) goes to active regions. Radioactivity gives off positrons that collide with electrons emitting 2 gamma rays. A detector surrounding the head picks up these rays. PET scans are commonly used with MRI scans to localize brain functions. Temporal resolution is relatively good, but spatial resolution is poor.
 

3) Functional MRI (fMRI): Use multiple MRI scans to detect changes in blood flow. Active brain areas use more blood. The MRI measures the resonance of the water in blood. Very goood spatial resolution and decent temporal resolution
 

4) Microelectrode recording: Insert an electrode into the brain and record the activity of neurons. Although this provides great temporal and spatial resolution, it is invasive and only one or a few neurons can be recorded at a time.
 

Researchers use these techniques to determine the location of specific functions. Franz Joseph Gall inspired a lot of interest in the location of brain functions in the 1800s with his work on phrenology. The goal of phrenology was to match personality traits to bumps on the skull (Figure 1.9).

There are several problems with phrenology:

a) The brain has no effect on the shape of the skull.
b) Complex tasks frequently require the use of many brain regions (i.e., they are not well localized). In contrast, simple things like sensory and motor systems are well localized There are three commonly used techniques to localize brain functions: a) Measure brain activity
b) Activate regions of the brain and measure output
c) Lesion parts of the brain and observe deficits     Myths about the brain:

Myth 1: Intelligence is determined by brain size.

Myth 2: A typical human only uses 10% of his or her brain.

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