Regional activation of human cerebral cortex upon an adaptation in mirror drawing.

To elucidate cerebral regions involved in adaptation to mirror drawing, changes in regional cerebral blood flow were measured using positron emission tomography at different levels of adaptation. A significant signal in subtraction images was localized in left Brodmann's area 45 (ventral sub-region of Broca's area) in the initial phase of the mirror drawing. This activity decreased as adaptation proceeded, and a small cluster in area 19 of the medial extrastriate cortex became significantly active. An after-effect of ca. 30 min of mirror-drawing was also detected in the right area 21 of the temporal association cortex. The results first demonstrated visuo-cortical regions where neurons might change their activity to evoke plastic response to the inverted vision.

Interpersonal influences in adolescent drug use--the role of older siblings, parents, and peers.

Drawing data from the first year of a longitudinal study of 508 families with focal adolescents aged 11 to 13 years and their older siblings (14 to 18 years), the investigators examined the influence of older siblings' drug-using attitudes and behaviors, in comparison with parental and peer drug-using attitudes and behaviors, on focal adolescents' nonuse and use of substances. Older siblings are frequently a source of drugs and use substances with their young siblings, though peers remain the primary source and the most frequent coursers. For most substances, frequency of use was predicted by older sibling and peer substance use, each after controlling for the other. Parental drug use was found to be minimal in comparison to older siblings and peers. Findings relative to the potentially important role of older siblings in influencing their younger siblings' drug-using behavior are discussed.

Brain activation in young and older adults during implicit and explicit retrieval.

Positron emission tomography was used to study regional cerebral blood flow (H2(15)O method) in groups of young and older adults during implicit and explicit retrieval, following a procedure devised by Squire et al. (1992). At study, subjects were exposed to four lists of words. Following list presentation, subjects were presented with three-letter word stems under four conditions: (1) silent viewing, (2) completion of word stems that could not form words from the study list, with the instruction to provide the first word that came to mind (baseline), (3) completion of word stems, half of which could form words from the study list, with the instruction to provide the first word that came to mind (priming), and (4) completion of word stems, half of which could form words from the study list, with the instruction to use the stems as cues for recall of list words (memory). The behavioral data indicated an agerelated deficit in cued recall that was reduced in priming. Both age groups showed a similar decrease of blood flow in right posterior cortex during priming relative to baseline. During cued recall, bilateral increases of blood flow were observed in prefrontal cortex and anterior cingulate gyrus for both age groups. The young adults showed selective increases of activity in left cerebellum and Wernicke's area, whereas the older adults showed a selective bilateral activation in the perirhinal region of the medial-temporal cortex during cued recall. The results suggest a simiiar biological basis of priming in both age groups: a decrease in the neural activity required to process a particular stimulus during a subsequent encounter compared with a previous one. In addition, the importance of prefrontal regions for conscious retrieval was substantiated and extended to late adulthood. Finally, the agedifferential activations observed during cued recall were discussed relative to prominent concepts in the current literature on cognitive aging (e.g., speed of processing, self-initiated operations, cross-modal recoding).