contd..

Martin et al. (1996) conducted a study to explore the role of motor region of the neo cortex in observing, remembering and imagining movements. PET images were used to identify brain regions active while various words were silently rehearsed. An increase in blood flow was observed in the hand region of motor cortex when subjects named tools. The researchers concluded that a connection exist between the hand region of motor cortex and knowledge about the tools and its usage.

Frey et al. (2000) performed PET study where the participants heard sound of violent car crash or familiar abstract sounds generated from an electronic keyboard. In another study novel abstract visual designs were presented to the participants and they had to memorize or just view them. Increased activation was observed in area 13 as a response to the unpleasant auditory stimuli. This area is connected to amygdale and hypothalamus. On the other hand, new visual information activated area 11. This has medial temporal cortical connections. A generalized prediction based on the study was that those with damage to area 13 would show weak response to threatening stimuli.

Maguire et al. (1997) performed PET scan for imaging hippocampus of the London taxi drivers. The taxi drivers were supposed to describe the route between two points in greater London and recall landmark buildings not in London and not visited. PET scan was performed while this process was on. Occipitotemporal areas, medial parital cortex, posterior cingulate cortex, parahippocampal gyrus and right hippocampus were activated during this spatial test. These drivers were also supposed to recall plot of a film and the result indicated that the non-spatial task did not activate the right hippocampus. A very important finding of this study was that the right posterior hippocampus increased in size as a function of years spent as a taxi driver. This shows the effect of topographic memory on human brain.

Drevets et al. (1997) studied mood disorder using PET. Cerebral blood flow of unmedicated unipolar, bipola and control subjects was examined using PET. 12% decrease in cerebral blood flow was recorded in the medial frontal region below the anterior region of the corpus callosum. The largest difference was observed in control and depressive groups.

PET scans have also been used for diagnosis of Alzheimer's and Parkinson's disease. It has emerged that certain regions of the brain show reduced blood flow (and hence metabolism) in the early stage of the disease. This pattern can be recorded years before the patient is diagnosed by a physician. The advantage of PET is that it provides visual image analogous to the brain anatomy and is helpful for functional and biochemical studies. It can also be useful to identify specific receptors associated with certain neurotransmitters. However, it exposes you to low levels of radioactivity. Also, it is not able to trail changes faster than 30 seconds. In addition, it has poor resolution as compared to MRI .