L/M speed-matching ratio predicts reading in children.

PURPOSE: Many behavioral studies have found impaired perception of dynamic visual stimuli in dyslexia and several neuroimaging studies have found reduced activation of the human motion area MT+ in dyslexia. These results are often interpreted as a magnocellular (MC) deficit in dyslexia. It has also been claimed that colored filters can help dyslexics to read. One defining feature of the MC-pathway is a greater weight for L-cone input than M-cone input, and at most very weak S-cone input. We measured the subjective speed matches between L-, M-, and S-cone isolating stimuli in good and poor readers. METHODS: Subjects performed a speed-matching task with drifting cone-isolating stimuli to find the point of subjective equality between two drifting patterns. Such a task is known to activate cortical area MT+, presumably via the MC-pathway. RESULTS: L- to M-cone speed-match ratios were negatively correlated with single-word (r=-0.46) and irregular-word reading (r=-0.56) but not with non-word reading. CONCLUSIONS: Results suggest that relative L-cone sensitivity within the MC-pathway may limit orthographic reading performance.     

Comparative PET studies of the kinetics and distribution of cocaine and cocaethylene in baboon brain.

Recent studies have suggested that cocaethylene, an active metabolite of cocaine found in blood and postmortem brain of individuals self-administering cocaine and alcohol, may play a role in the increased toxicity seen when coadministering these 2 drugs. We have used positron emission tomography (PET) and carbon-11 (t1/2:20.4 min) labeled cocaine and cocaethylene to compare the short-term kinetics of cocaine and cocaethylene in baboon brain. The regional uptake of [11C]cocaine cocaethylene in baboon brain. The regional uptake of [11C]cocaine ([11C]COC) and [11C]cocaethylene ([11C]CE), 5-8 mCi and 4-6 micrograms, in baboon brain (n = 7) were similar but clearance from whole brain (global, GL) and from striatum (SR), thalamus (TH), and cerebellum (CB) was slower for cocaethylene. Steady-state distribution volumes (DV) were not significantly different in the striatum but were greater for cocaethylene in the thalamus, cerebellum, and whole brain. Debenzoylation of cocaethylene proceeded at about one-third the rate of cocaine, as determined by in vitro incubation of labeled cocaethylene and labeled cocaine with baboon plasma and with purified horse butyryl-cholinesterase (EC 3.1.1.8). Even though the slower clearance of cocaethylene could lead to longer tissue exposures and potentially accentuated or different physiological effects relative to cocaine, the difference between the 2 drugs is not large. Thus it is more likely that the direct actions of cocaine and alcohol on some organs, rather than cocaethylene, account for this enhanced toxicity.     

A portable system for measuring cutaneous thresholds for warming and cooling.

Measurement of cutaneous thermal thresholds is a valuable technique for detecting small fibre neuropathy. A robust and portable microcomputer controlled system, which separately measures thresholds for warming and cooling, is described. Thresholds at three sites have been measured; the cheek, the dorsum of the hand and the sole of the foot. Regional variability and a correlation with age have been found, indicating the sensitivity of this system.     

'What do you notice?' Using posters containing questions and general instructions to guide preschoolers' science and mathematics learning

To increase preschoolers' science and mathematics learning experiences both within and outside the classroom, we developed age-appropriate materials containing general questions and instructions that teachers and parents could use when interacting with their students and children. The questions and instructions were related to a specific science or mathematics skill (e.g., classifying), but were general enough so that they could be applied to a variety of situations. Observations of three classrooms and interviews with the classroom teachers and aides, and the parents of the children in the classrooms suggested that use of these materials was beneficial to the children, teachers, and parents, and resulted in increasing the amount of science and mathematics activities and discussions in two of the classrooms as well as outside the classrooms.     

Nontuberculous mycobacteria in bronchiectasis: Prevalence and patient characteristics.

The aim of the current study was to investigate the prevalence and clinical associations of nontuberculous mycobacteria (NTM) in a well-characterised cohort of patients with adult-onset bronchiectasis. The sputum of all patients attending a tertiary referral bronchiectasis clinic between April 2002 and August 2003 was examined for mycobacteria as part of an extensive diagnostic work-up. NTM-positive patients subsequently had further sputa examined. A modified bronchiectasis scoring system was applied to all high-resolution computed tomography (HRCT) scans from NTM-positive patients, and a matched cohort without NTM. Out of 98 patients attending the clinic, 10 had NTM in their sputum on first culture; of those, eight provided multiple positive cultures. Three patients were treated for NTM infection. A higher proportion of NTM-positive than -negative patients were subsequently diagnosed with cystic fibrosis (two out of nine versus two out of 75). On HRCT scoring, more patients in the NTM-positive group had peripheral mucus plugging than in the NTM-negative group. In the current prospective study of a large cohort of patients with bronchiectasis, 10% cultured positive for nontuberculous mycobacteria in a random clinic sputum sample. Few clinical parameters were helpful in discriminating between groups, except for a higher prevalence of previously undiagnosed cystic fibrosis and of peripheral mucus plugging on high-resolution computed tomography in the nontuberculous mycobacteria group.     

Fructose metabolism in the adult mouse optic nerve, a central white matter tract.

Our recent report that fructose supported the metabolism of some, but not all axons, in the adult mouse optic nerve prompted us to investigate in detail fructose metabolism in this tissue, a typical central white matter tract, as these data imply efficient fructose metabolism in the central nervous system (CNS). In artificial cerebrospinal fluid containing 10 mmol/L glucose or 20 mmol/L fructose, the stimulus-evoked compound action potential (CAP) recorded from the optic nerve consisted of three stable peaks. Replacing 10 mmol/L glucose with 10 mmol/L fructose, however, caused delayed loss of the 1st CAP peak (the 2nd and 3rd CAP peaks were unaffected). Glycogen-derived metabolic substrate(s) temporarily sustained the 1st CAP peak in 10 mmol/L fructose, as depletion of tissue glycogen by a prior period of aglycaemia or high-frequency CAP discharge rendered fructose incapable of supporting the 1st CAP peak. Enzyme assays showed the presence of both hexokinase and fructokinase (both of which can phosphorylate fructose) in the optic nerve. In contrast, only hexokinase was expressed in cerebral cortex. Hexokinase in optic nerve had low affinity and low capacity with fructose as substrate, whereas fructokinase displayed high affinity and high capacity for fructose. These findings suggest an explanation for the curious fact that the fast conducting axons comprising the 1st peak of the CAP are not supported in 10 mmol/L fructose medium; these axons probably do not express fructokinase, a requirement for efficient fructose metabolism.