Conjoint and extended neural networks for the computation of speech codes: the neural basis of selective impairment in reading words and pseudowords

The computation of speech codes (i.e. phonology) is an important aspect of word reading. Understanding the neural systems and mech- anisms underlying phonological processes provides a foundation for the investigation of language in the brain. We used high-resolution three-dimensional positron emission tomography (PET) to investigate neural systems essential for phonological processes. The burden of neural activities on the computation of speech codes was maximized by three rhyming tasks (rhyming words, pseudowords and words printed in mixed letter cases). Brain activation patterns associated with these tasks were compared with those of two baseline tasks involving visual feature detection. Results suggest strong left lateralized epicenters of neural activity in rhyming irrespective of gender. Word rhyming activated the same brain regions engaged in pseudoword rhyming, suggesting conjoint neural networks for phonological processing of words and pseudowords. However, pseudoword rhyming induced the largest change in cerebral blood flow and activated more voxels in the left posterior prefrontal regions and the left inferior occipital-temporal junction. In addition, pseudoword rhyming activated the left supramarginal gyrus, which was not apparent in word rhyming. These results suggest that rhyming pseudowords requires active participation of extended neural systems and networks not observed for rhyming words. The implications of the results on theories and models of visual word reading and on selective reading dysfunctions after brain lesions are discussed.     

Endoscopic removal of a suprasellar arachnoid cyst: an anatomical study with special reference to skull base

Background  

Suprasellar arachnoid cysts are rare entities in adults, representing 10% of all cysts. Endoscopic treatment is now preferred for this pathology, allowing a new anatomical approach to skull base structures.     

Select Acetophenones Modulate Flagellar Motility in Chlamydomonas

Acetophenones were screened for activity against positive phototaxis of Chlamydomonas cells, a process that requires co-ordinated flagellar motility. The structure–activity relationships of a series of acetophenones are reported, including acetophenones that affect flagellar motility and cell viability. Notably, 4-methoxyacetophenone, 3,4-dimethoxyacetophenone, and 4-hydroxyacetophenone induced negative phototaxis in Chlamydomonas, suggesting interference with activity of flagellar proteins and control of flagellar dominance.     

Internal structure of sleep cycles in a healthy population

A large body of data has been gathered on the sleep characteristics of normal subjects. The evolution of each sleep stage within each NREM/REM cycle is presented in detail, showing stage intensities minute by minute. There is a three-phase pattern in each stage intensity diagram: an initial phase of rapid change; a central phase of relative stability; and a terminating phase, again, of rapid change. The details of this pattern change progressively during the night. Throughout all cycles, there is a complementary relationship between the intensities of stage 2 sleep and the other stages that underlines the central role of stage 2 sleep in all stage transitions. Stage intensity diagrams for two groups, one group with and one group without stage 4 sleep, were compared. Subjects without stage 4 sleep tended to have a shorter duration and greater latency of stage 3 sleep. Surprisingly, cycles interrupted by abnormally long periods of continuous wake showed a negative correlation between the intensities of wake and slow wave sleep, and these interruptions did not appear to reset the cycle clock to zero. Sleep stage intensity diagrams may be useful to study the sleep patterns of populations of insomniac and depressive patients, as well as the effect of drugs on sleep.     

Hemoglobin/hematocrit and other erythrocyte parameters

The authors review erythrocyte physiology, blood collection, and laboratory methodology for enumerating blood cells. The clinical interpretation of abnormal erythrocyte parameters is discussed, and the emergency department approach to anemia and polycythemia is detailed.     

Postbiopsy renal transplant arteriovenous fistulas: color Doppler US characteristics

Color Doppler ultrasound (US) with point-spectral analysis was performed on eight patients with postbiopsy renal transplant arteriovenous fistulas. Waveform analysis of the supplying artery documented decreased resistive indices in all cases and increased flow velocities in seven. The peak-systolic flow velocity in the arteries supplying the fistulas ranged from 55 to 180 cm/sec (mean, 92 cm/sec), while the range in normal arteries was 20-52 cm/sec (mean, 32 cm/sec). The resistive indices of the arteries supplying the fistulas ranged from 0.31 to 0.50 (mean, 0.45), while the resistive indices of the normal arteries ranged from 0.60 to 0.92 (mean, 0.74). Arterialization of the venous waveform from the draining vein was also documented in all cases. In six cases, the increased flow velocities resulted in increased color saturation toward white in the supplying artery (n = 2) or in both the artery and the draining vein (n = 4), which was detectable on the realtime image. In six cases, flow turbulence resulted in localized tissue vibration, which appeared as random color assignment in extravascular renal parenchyma adjacent to the fistula. Knowledge of these imaging and Doppler characteristics should aid in the identification of renal transplant arteriovenous fistulas with color Doppler US.     

Task and driving performance of patients with a severe concussion of the brain

Patients who had sustained a severe concussion of the brain more than 2 years earlier were tested in choice reaction time tasks in the laboratory in order to investigate their impaired reactive capacity. The focus of investigation was whether specific stages in the chain of the information process are affected by the injury. In addition, driving skills were measured in an instrumented car to determine if reaction time performance is predictive of car driving. In general, patients were much slower than control subjects, both in the reaction time and in the driving tasks. The results obtained in the reaction time tasks provide no conclusive evidence, however, that severe concussion of the brain affects particular stages in information processing. Reaction time tasks appear to have predictive value for the ability to drive a car.     

Stimulation of the hypothalamo-pituitary-adrenocortical axis by the central serotonergic pathway: involvement of endogenous corticotropin-releasing hormone but not vasopressin.

Many reports indicate that serotonin plays a role in the regulation of the hypothalamo-pituitary-adrenocortical axis. The present study was designed to elucidate whether the activation of the central serotonergic pathway enhances adrenocorticotropin and corticosterone secretion, and if so, whether the CRH and vasopressin neuronal systems could be mediating this effect. Intraperitoneal administration of a low dose of L-5-hydroxytryptophan (an aromatic L-amino acid precursor of serotonin synthesis; 20 mg/kg bw, 30 minutes before the sacrifice) in rats pretreated with pargyline (a brain monoamine oxidase inhibitor, which enhances monoamine activity; 75 mg/Kg bw, 16 hours before the sacrifice) and carbidopa (a peripheral active inhibitor of the decarboxylation of aromatic L-amino acids, which would permit more monoamine precursor to be available to the brain; 50 mg/Kg bw, 90 minutes before the sacrifice) increased ACTH and corticosterone secretion in plasma. Such an effect was partially blocked by metergoline (a serotonin type-1 and-2 receptor blocker; 1 mg/Kg bw, 90 minutes before the sacrifice), but not by spiperone (a serotonin type-2 and dopamine receptor antagonist; 0.5 mg/Kg bw. 90 minutes before the sacrifice). The activation of the central serotonergic system enhanced the CRH content in the median eminence, whereas it decreased the content of this neuropeptide in the medial basal hypothalamus. These effects were fully abolished by metergoline, but not by spiperone pretreatment. The activation of the serotonergic pathway did not influence the vasopressinergic neuronal system. In vitro experiments using hypothalamic-median eminence fragments incubated with serotonin solutions indicate that this monoamine possesses a CRH releasing effect at concentrations of 1 microM or more.(ABSTRACT TRUNCATED AT 250 WORDS)