The section utilizes positron emission tomography (PET), magnetic resonance imaging (fMRI), and transcranial magnetic stimulation (rTMS) to map planning processes, representational knowledge, reasoning processes, time perception, reward systems, number processing and calculation, and many other cognitive processes to brain. For example, over the last year, we have determined with PET that maze traversal does not require the activation of planning processes stored in prefrontal cortex unless part of the maze is hidden from view. Analogical processing studies using PET have indicated that left prefrontal cortex is particularly important for the analogical mapping process itself. Other PET studies have examined the mental imagery of aggressivity and three-dimensional maze traversal. We have confirmed with fMRI the importance of left inferior parietal cortex for subserving calculation processes. On the other hand, we have been unsuccessful in accurately localizing the cognitive processes required for number magnitude estimation. With fMRI, we have noted that the processing of emotional words appears to activate anterior temporal lobe and inferior frontal lobe structures not ordinarily activated by reading non-emotional words. fMRI experiments examining estimation of time duration have found that local areas of cortex may compute their own time constants that are compatible with their information processing capabilities. Neuroplasticity fMRI and PET studies have demonstrated that islands of spared tissue in a damaged hemisphere may inhibit adaptive plasticity in the unaffected hemisphere. However, sensory deprivation fMRI experiments in normal volunteers did not reliably induce neuroplastic changes. rTMS studies have indicated that linguistic processing, independent of speech motor functions, can be interfered with by trains of magnetic stimuli and that this interference affects items in a psycholinguistically systematic way.
