Practice of a novel task leads to improved performance. The brain mechanisms associated with practice-induced improvement in performance are largely unknown. To address this question we have examined the functional anatomy of the human brain with positron emission tomography (PET) during the naive and practiced performance of a simple verbal response selection task (saying an appropriate verb for a visually presented noun). As a control state, subjects were asked to repeat the visually presented nouns. Areas of the brain most active during naive performance (anterior cingulate, left prefrontal and left posterior temporal cortices, and the right cerebellar hemisphere), compared to repeating the visually presented nouns, were all significantly less active during practiced performance. These changes were accompanied by changes in the opposite direction in sylvian-insular cortex bilaterally and left medial extrastriate cortex. In effect, brief practice made the cortical circuitry used for verbal response selection indistinguishable from simple word repetition. Introduction of a novel list of words reversed the learning-related effects. These results indicate that two distinct circuits can be used for verbal response selection and normal subjects can change the brain circuits used during task performance following less than 15 min of practice. One critical factor in determining the circuitry used appears to be the degree to which a task is learned or automatic.

Regional cerebral blood flow, an index of local neuronal activity, was measured using positron emission tomography (PET) during the performance of the classic Stroop color/word task in eight healthy right-handed subjects.In the first condition of this paradigm, subjects name the color of the words presented on a video monitor. All the words are the color names congruent to the color presented (e.g., the noun "red" displayed in red color). In the second condition, subjects also name the color of the words presented on the monitor. However, during these trials all words are color names incongruent to the color presented (e.g., the noun "red" displayed in green color). The difference in brain activity between these two conditions (i.e., incongruent minus congruent) could reveal brain systems involved in the attentionally mediated resolution of the conflict between the habitual response of reading words vs. the task demands of naming the color of the words-i.e., the Stroop interference effect. The most robust responses occurred in the anterior cingulate cortex. Other responses noted were in the left premotor cortex, left postcentral cortex, left putamen, supplementary motor area, right superior temporal gyrus, and bilateral peristriate cortices. These data provide support for the role of the anterior cingulate cortex in attentional processing through the selection and recruitment of processing centers appropriate for task execution. Furthermore, the extensive distributed network of activated regions suggests that the Stroop interference effect cannot be explained simply in terms of stimulus encoding or response interference.The Stroop task (1, 2) is a classic experimental paradigm used in behavioral neuroscience in both clinical and research settings. Subjects note the strong interference of word reading upon color naming, called the Stroop interference effect, when a noun presented is a color name displayed visually using a different color (see Fig. 1 What are the likely anatomical loci and associated cognitive operations involved in attentional conflict paradigms such as the Stroop task? Two general areas are suggested on the basis of data from several sources: the prefrontal cortex and the anterior cingulate. The prefrontal cortex, based on experimental evidence from both monkeys as well as humans (4, 5), has been demonstrated to be important not only for memory buffering to permit "on-line" processing but also for inhibition of "prepotent" habitual, albeit sometimes inappropriate, responses. Lesions of the left prefrontal cortex result in impaired performance in the Stroop task (6). Linguistic tasks requiring the inhibition of reading a noun and the generation of a verb appropriate to the noun result not only in activation of the left prefrontal cortex but also the anterior cingulate (7,8). Some human diseases, such as schizophrenia, involving prefrontal (9) and anterior cingulate abnormalities (10) result in impairments in attentional conflict paradigms (11).Recent technological advances in nuclear medi...

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Electrophysiologic and lesion studies of animals increasingly implicate the amygdala in aspects of emotional processing. Yet, the functions of the human amygdala remain poorly understood. To examine the contributions of the amygdala and other limbic and paralimbic regions to emotional processing, we exposed healthy subjects to aversive olfactory stimuli while measuring regional cerebral blood f low (rCBF) with positron emission tomography. Exposure to a highly aversive odorant produced strong rCBF increases in both amygdalae and in the left orbitofrontal cortex. Exposure to less aversive odorants produced rCBF increases in the orbitofrontal cortex but not in the amygdala. Change of rCBF within the left amygdala and the left OFC was highly intercorrelated, indicating a strong functional interaction between these brain regions. Furthermore, the activity within the left amygdala was associated significantly with subjective ratings of perceived aversiveness. These findings provide evidence that the human amygdala participates in the hedonic or emotional processing of olfactory stimuli.

We have found that vinculin is localized at the sarcolemma of skeletal muscle cells in a two-dimensional orthogonal lattice. Perpendicular to the longitudinal axis of the cell, bands of vinculin encircle the muscle cell and repeat along its length with a periodicity corresponding to the subjacent sarcomeres. Because oftheir appearance and probable function, we call the transverse elements of the lattice "costameres" (Latin costa, rib; Greek meros, part). Costameres have a substructure consisting of densely clustered patches of vinculin; the patches are segregated into two rows which flank the Z line and overlie the I band of the underlying sarcomere. It is likely that the costameres are physically coupled to the underlying myofibrils because: (i) the costameres broaden and narrow in concert with the underlying I band in stretched and contracted muscle, and (ii) adjacent but misaligned myofibrils are mirrored by corresponding discontinuities in the overlying costameres. We hypothesize that the sarcolemmal lattice, detected because vinculin is one of its molecular components, integrates the contractile apparatus with the sarcolemma during lengthening and shortening of the muscle cells.Vinculin (1) has been implicated in cytoskeleton-to-membrane attachment because the smooth muscle protein binds actin (2, 3) and because, in a variety of cell types, vinculin is located at specialized regions where microfilaments abut the plasma membrane. Some examples ofthese specialized regions include the plasma membrane-associated dense plaques ofsmooth muscle cells (4), the fascia adherens ofcardiocytes (5), focal adhesion plaques offibroblasts (1,(6)(7)(8), and the zonulae adherens of the junctional complex in epithelial cells (9).In this paper, we report that vinculin defines a striking, twodimensional lattice associated with the sarcolemma of skeletal muscle cells. Like the hoops and staves of a barrel, this cortical lattice has both longitudinal elements and transverse circumferential elements. We present evidence that the transverse elements of the sarcolemmal lattice ("costameres," from Latin costa, rib, and Greek meros, part) are coupled to the myofibrils.MATERIALS AND METHODS Vinculin was purified to at least 93% homogeneity from frozen (-20°C) glycerinated central muscles of chicken gizzards (10) and used to purify vinculin antibody from rabbit antisera (11). The antibody was tested on immunoblots of total NaDodSO4-soluble muscle proteins separated by NaDodSO4/polyacrylamide gel electrophoresis (12, 13). Thaw-mounted 4-pkm cryostat sections were fixed in phosphate-buffered 3% (wt/vol) paraformaldehyde for 5 min and stained as will be described elsewhere, except that p-phenylenediamine was used to delay fluorescence quenching (14). In control staining protocols, affinity-purified anti-keyhole limpet hemocyanin was used as the first-step antibody. Affinity-purified, fluorescein-coupled, goat anti-rabbit IgG was purchased from Boehringer Mannheim and used as the second-step antibody. Some 4-,um cryostat sections o...