There are approximately 30 visual areas after V1. The functional specialization hypothesis drives much of the research about these areas. Some areas seem specialized for processing a certain aspect of visual information. E.g., MT - motion, V4 - color (?).
- Cortical areas dedicated to vision are densely interconnected, and can seem quite confusing at first glance.
- However, a more general organization is evident in a pair of parallel pathways.
- What pathway. Temporal lobe; recognition of objects.
- Where pathway. Parietal lobe; motion, spatial orientation, localization.
Interlude. Methods for Measuring Brain Activity
- Methods of historical interest. Blood flow is selectively increased in parts of the brain that are active. Mosso (late 1800s) measured "brain pulsations" in infants, and found larger pulsations during periods of mental activity.
- Electrophysiology. Can be done at the single-cell level in research animals. Invasive technique using an electrode implanted into cortex to measure neuronal spikes.
- Optical imaging. Measure of blood flow. By opening the animal's skull, pointing a video camera at the exposed cortex, and collecting images that reflect the amount of oxygenated and deoxygenated blood researchers can measure the activity of a section of brain.
- PET = "positron emission tomography". Subject is injected with a mild radioactive substance and lies in a PET scanner. Because blood is directed to areas of increased activity, more radioactive substance ends up in the active areas, and the PET scanner detects this.
- fMRI = "functional magnetic resonance imaging". Just as a regular MRI machine can be used to image soft tissue in your knee, it can be fine-tuned to detect relative changes in the concentration of oxygenated and deoxygenated blood in the brain. Therefore, we can detect areas of increased neural activity. This technique is non-invasive (no surgery, no radiation), so it is the current technique of choice for measuring brain activity in humans.
- EEG = "electroencephalograph". Electrodes placed on the scalp detect small changes in electrical activity. However, it is difficult to localize the source of these electrical signals.
Last modified: Tue Jun 29 10:58:53 PDT