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Biomedical subjects

K Specht

Publications and source records attributed to K Specht.

24 records · Page 2Linked to original sources
PubMed1999

Functional anatomy of intrinsic alertness: evidence for a fronto-parietal-thalamic-brainstem network in the right hemisphere.

Alertness, the most basic intensity aspect of attention, probably is a prerequisite for the more complex and capacity demanding domains of attention selectivity. Behaviorally, intrinsic alertness represents the internal (cognitive) control of wakefulness and arousal; typical tasks to assess optimal levels of intrinsic alertness are simple reaction time measurements without preceding warning stimuli. Up until now only parts of the cerebral network subserving alertness have been revealed in animal, lesion, and functional imaging studies. Here, in a 15O-butanol PET activation study in 15 right-handed young healthy male volunteers for this basic attention function we found an extended right hemisphere network including frontal (anterior cingulate-dorsolateral cortical)-inferior parietal-thalamic (pulvinar and possibly the reticular nucleus) and brainstem (ponto-mesencephalic tegmentum, possibly involving the locus coeruleus) structures, when subjects waited for and rapidly responded to a centrally presented white dot by pressing a response key with the right-hand thumb.

Adult↗
PubMed1998

A parametric analysis of the 'rate effect' in the sensorimotor cortex: a functional magnetic resonance imaging analysis in human subjects.

We studied the effects of different movement speeds of unimanual right hand movements on functional magnetic resonance signal changes in the sensorimotor cortex using echo planar imaging (EPI). Six healthy right-handed subjects were scanned at rest and while executing a finger tapping task with their right index finger. Movement frequency was visually paced at rates ranging from 0.5 to 5 Hz, separated by 0.5 Hz steps. The blood oxygen level dependent (BOLD) response within the left sensorimotor cortex was linearly and positively related to movement frequency. However, this relation holds (r2 = 0.91) only for movement frequencies faster than 1 Hz (1.5-5 Hz). For the slower frequencies there was an initial sharp increase of the BOLD response from 0.5 to 1 Hz followed by an activity drop for 1.5 Hz. These results are compatible with the idea that two different motor control modes are operative during slow or fast movements. During slow movements a computational demanding on-line feedback control mode is operative resulting in strong BOLD signals indicating extensive neural activity. During faster movements on the other hand a program-like motor control mode is operative resulting in less demanding neural computations. The amount of neural computation for the latter control mode increases with increasing movement speed.

Adult↗
PubMedDate not supplied

Synergistic activity of benzoyl peroxide and erythromycin.

BACKGROUND: Benzoyl peroxide (BP) is the most widely used topical agent for acne since its introduction in the 1960s. Concomitant topical treatment of BP and erythromycin is stated to be superior to BP alone. However, no synergistic activity has been found with this combination. Instead, such combination therapies are hypothesized to gain their efficacy by the coupled action of two effective treatments. The antibiotic kills all susceptible bacteria and the BP eliminates the resistant strains. OBJECTIVE: The purpose was to compare radical production by BP alone and with various antibiotics to determine whether certain antibiotics increase radical formation by BP, as the antibacterial activity of BP may correlate with the amount of radicals it forms. METHODS: Polymerization of tetraethylene glycol dimethacrylate was used as a test of BP radical activity. RESULTS: The results suggest that radical activity increases upon addition of certain antibiotics, such as erythromycin, to a solution of BP. CONCLUSION: Radical activity of BP in tetraethylene glycol dimethacrylate is increased when tested in consort with several antibiotics, such as the macrolides. We propose that the tertiary amines contained on certain antibiotics are responsible for catalysis of BP radical formation. If increased radical formation correlates with enhanced biological effect, then these data reveal the possibility of a biological synergism in mixtures of BP and antibiotics. An understanding of the mechanism of catalysis of BP radical formation by antibiotics may lead to the discovery of improved treatments for acne.

Acne Vulgaris↗