Assignment: Neuroscientific Research Methods
Assignment: Modern Neuroscientific Research Methods
1.5 Modern Neuroscientific Research Methods
Early investigators used two techniques to study the brain: lesioning and stimulation. Lesioning involves damaging or disrupting the function of a particular area of the brain. If a region of the brain is destroyed, then it cannot perform its usual function. The investigator would typically produce a lesion in an area of interest in the brain of an anesthetized animal. When the experimental subject recovered from the surgery, the investigators observed its behavior for any signs of impairment. Lesioning, then, demonstrates what happens when a brain structure is not functioning normally.
Most of the earliest lesioning studies involved ablation, or removal of a part of the brain. In the first studies, the brain region to be removed was merely ladled out with a sharp spoon. However, this rather crude procedure created a bruised area in the brain that became scarred and prone to produce epileptic seizures. Karl Lashley, the American psychologist you learned about earlier in this chapter, used a technique called hot wire thermocautery. After preparing his subject for the procedure, which involved anesthetizing it and opening its skull, Lashley placed the tip of a red-hot wire in the brain to burn away the area to be lesioned. This technique produced a neat lesion with little bleeding, but it did not eliminate scarring, which caused uncontrollable seizures.
Wilder Penfield perfected a suctioning technique to lesion the brains. He used a pipette, which looks like a medicine dropper, to draw out the brain tissue. This technique was superior to Lashley’s because it produced minimal, if any, scarring. All brain cells that did not have a good blood supply were easily removed, which meant that no dead tissue was left in the brain after surgery. Penfield’s suctioning technique is still used today by neurosurgeons and neuroscience investigators to remove brain matter.
Ablation techniques work fine when a cortical area of the brain is under investigation. However, an entirely different technique is needed when lesioning a structure beneath the cortex, called a subcortical brain structure. Think about the problems that would be encountered in lesioning a subcortical structure. First of all, the subcortical structure is not visible when the skull is opened, and it has to be located underneath the overlying cortex. In addition, care must be taken to lesion the subcortical structure without damaging the overlying brain. How is it possible to locate and lesion subcortical structures?
Think about how you might get to a city that you have never visited before. For starters, you might ask a friend how to get there, or you could pick up a road atlas and locate the city. And that’s exactly how brain investigators find unfamiliar brain structures: They consult with a colleague or read a published paper that describes another scientist’s research on that structure, or they use a stereotaxic brain atlas. A stereotaxic brain atlas contains dozens of maps of the brain, each map representing a slice through a particular region of the brain. There are atlases for human brains, dog brains, cat brains, rat brains, monkey brains, and even several species of bird brains.
An apparatus called the stereotaxic instrument was developed in 1908 by Victor A. H. Horsley and Robert H. Clarke to enable investigators to locate brain structures with precision. Because subcortical structures can be quite small, they are easy to miss if measurements are not precise.
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