The results suggest that emotions associated with the PTSD symptomatic state are mediated by the limbic and paralimbic systems within the right hemisphere. Activation of visual cortex may correspond to the visual component of PTSD reexperiencing phenomena.

These findings are consistent with results of previous functional neuroimaging studies and contemporary neurocircuitry models of OCD. The data further implicate orbitofrontal cortex, caudate nucleus, and anterior cingulate cortex in the pathophysiology of OCD and in mediating OCD symptoms.

We used positron emission tomography (PET) to examine the role of the hippocampal formation in implicit and explicit memory. Human volunteers studied a list of familiar words, and then they either provided the first word that came to mind in response to three-letter cues (implicit memory) or tried to recall studied words in response to the same cues (explicit memory). There was no evidence of hippocampal activation in association with implicit memory. However, priming effects on the implicit memory test were associated with decreased activity in extrastriate visual cortex. On the explicit memory test, subjects recalled many target words in one condition and recalled few words in a second condition, despite trying to remember them. Comparisons between the two conditions showed that blood-flow increases in the hippocampal formation are specifically associated with the conscious recollection of studied words, whereas bloodflow increases in frontal regions are associated with efforts to retrieve target words. Our results help to clarify some puzzles concerning the role of the hippocampal formation in human memory.Understanding the role of the hippocampal formation in learning and memory constitutes an enduring problem in cognitive neuroscience. Studies of brain-damaged amnesic patients implicate the hippocampal formation in explicit or conscious memory for past events. By contrast, the hippocampal formation is thought to be uninvolved in a nonconscious or implicit form of memory known as priming (1-4). Yet previous attempts to test these ideas directly by studying the normal human brain with positron emission tomography (PET) have yielded inconclusive results.In an early PET study by Squire et al. (5), subjects studied a list of familiar words (e.g., GARNISH) and were then tested with three-letter word stems (e.g., GAR-). When subjects were instructed to provide a word from the study list on a cued recall test (explicit memory), there were significant blood flow increases in the vicinity of the right hippocampal formation compared with a baseline condition in which subjects responded to stems of nonstudied words. In a separate scan conducted in the same experimental session, subjects were instructed to complete stems of previously studied words with the first word that comes to mind (implicit memory), and a priming effect was observed: subjects preferentially completed the stems with words from the study list. Compared with the baseline condition, priming was associated with decreased blood flow in extrastriate occipital cortex and increased blood flow in the right hippocampus/parahippocampal gyrus. Because amnesic patients with hippocampal damage show intact priming effects (6-8), the former finding is consistent with the idea that such effects are mediated by brain systems outside the

This study used a linear structural relations modeling technique (LISREL) to examine longitudinal data for 1,192 persons from a community-based population. The goal was to test the ability of an a priori model to predict cognitive change over a 2.0- to 2.5-year period in older adults aged 70-79 at the initial evaluation. The model included 22 demographic, physical, and psychosocial variables as predictors of cognitive function and cognitive change. The study used an exploratory-confirmatory design, enabling cross-validation of the model developed in the exploratory set in the confirmatory sample. Structural equation modeling analyses identified 4 endogenous model variable (education, strenuous activity, peak pulmonary expiratory flow rate, and self-efficacy) as direct predictors of cognitive change over the study period.

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