The cerebral organization of word identification processes in reading was examined using functional magnetic resonance imaging (fMRI). Changes in fMRI signal intensities were measured in 38 subjects (19 males and 19 females) during visual (line judgement), orthographic (letter case judgement), phonological (nonword rhyme judgement) and semantic (semantic category judgement) tasks. A strategy of multiple subtractions was employed in order to validate relationships between structure and function. Orthographic processing made maximum demands on extrastriate sites, phonological processing on a number of frontal and temporal sites, and lexical-semantic processing was most strongly associated with middle and superior temporal sites. Significant sex differences in the cerebral organization of reading-related processes were also observed.

This study linked 2 experimental paradigms for the analytic study of reading that heretofore have been used separately. Measures on a lexical decision task designed to isolate phonological effects in the identification of printed words were examined in young adults. The results were related to previously obtained measures of brain activation patterns for these participants derived from functional magnetic resonance imaging (fMRI). The fMRI measures were taken as the participants performed tasks that were designed to isolate orthographic, phonological, and lexical-semantic processes in reading. Individual differences in the magnitude of phonological effects in word recognition, as indicated by spelling-to-sound regularity effects on lexical decision latencies and by sensitivity to stimulus length effects, were strongly related to differences in the degree of hemispheric lateralization in 2 cortical regions.

Advances in information concerning brain function in animals and advances in analytical neurochemical methods for determining extremely low levels of compounds in physiological fluids have opened great opportunities for clinical neurochemical studies of autism. Nevertheless, the behavioral deficits in autistic individuals are major obstacles to clarification of the relations between symptoms and biochemical dysfunction in the brain. The fundamental preclinical and clinical studies of serotonin, dopamine, and norepinephrine metabolism related to infantile autism are reviewed, and new studies are suggested as examples of the productive strategies that will illuminate features of the autistic syndrome in the next decade.

The relative contribution of dopamine (DA) and norepinephrine (NE) in behavioral arousal was examined in developing rat pups using intracisternal 6-hydroxydopamine (6-OHDA) either alone or following pretreatment with desmethylimipramine (DMI). Such treatments were designed to examine the effects of preferential reduction of DA (DA depletion), NE (NE depletion), or both catecholamines (CA depletion) in the development of motor activity and escape performance. General motor activity increased with age and, over all ages, DA-depleted pups tended to exhibit greater activity. This was most apparent at 15 days of age, where DA-depleted pups were significantly more active than controls, NE-depleted, or CA-depleted pups. DA-depleted pups failed to exhibit the steep decline in activity over time (habituation of activity) demonstrated by the control and NE-depleted pups, while pups depleted of both CA fell into an intermediate position in habituation. Escape latency in a T-maze at 20 days and shuttle box at 26 days of age indicated comparable performance to controls for NE-depleted pups, while those animals in DA-depleted and CA-depleted groups appeared unable to perform the task. Brain CA concentrations (determined by a radioenzymatic assay) indicated preferential reduction of DA in the DA-depleted group to concentrations 25% of controls, reduction of NE to 62% of controls in the NE-depleted group, and reductions of DA to 42% and NE to 60% in the CA-depleted group. These results suggest that preferential reduction of brain DA in the developing rat pup increases motor activity and impairs habituation of activity during the stage of behavioral arousal in week 3 of postnatal life.(ABSTRACT TRUNCATED AT 250 WORDS)

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