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Biomedical subjects

L B Cohen

Publications and source records attributed to L B Cohen.

At least 91 records · Page 5Linked to original sources
PubMed1977

Changes in absorption, fluorescence, dichroism, and Birefringence in stained giant axons: : optical measurement of membrane potential.

The absorption, fluorescence, dichroism, and birefringence of stained squid axons were measured during action potentials and voltage clamp steps in an effort to find large optical signals that could be used to monitor membrane potential. Changes in all four optical properties were found that were linearly related to membrane potential and, with several new dyes, the signal-to-noise ratios were larger than any obtained previously. The problem of photodynamic damage was greatly diminished; with a merocyaninerhodanine dye, the photodynamic damage associated with intense light and the presence of oxygen was negligible. The absorption change obtained with this dye was relatively large; it could be measured with a signal-to-noise ratio of 100:1 during a single action potential.

Action Potentials↗
PubMed1977

An examination of interference effects in infants' memory for faces.

2 experiments with 18-week-old infants employed an interference paradigm to study infant visual memory. The infants were habituated to a repeated stimulus, given several trials with 1 or more interpolated stimuli, and then tested for recognition of the original stimulus. In Experiment 1, both amount of exposure and the similarity of the potentially interfering material to the original habituation stimulus were manipulated. Neither produced a significant interference effect, although some effect may have been shown by subjects who habituated to the interference stimult did demonstrate more clearly long-term retention of the originally remembered material. It was concluded from both studies that infant visual memory is a robust phenomenon, relatively immune to interference under most conditions.

Attention↗
PubMed1975

Purification and properties of a ribosomal protein methylase from Eschericha coli Q13.

Ribosomal protein methylase has been purified from Escherichia coli strain Q13 using methyl-deficient 50S subunits as substrates. The purified enzyme (or enzyme complex) which is devoid of rRNA methylating activity is quite stable and has a pH optimum around 8.0. The Km for S-adenosyl-L-methionine is 3.2 muM. The molecular weight of the enzyme is 3.1 X 10(4); minor methylating activity was also detected for protein peaks with molecular weights of 1.7 X 10(4) and 5.6 X 10(4). Protein L11 is the major protein methylated by the purified enzyme. Product analysis revealed the presence of N epislon-trimethyllysine, a methylated neutral amino acid(s) previously observed in protein L11 and N epislon-monomethyllysine. Free ribosomal proteins were much better substrates for the methylation, indicating that methylation of 50S ribosomal proteins can occur before the complete assembly of the 50S ribosomal subunit.

Escherichia coli↗
PubMed1975

Infants' development of object permanence: a refined methodology and new evidence of Piaget's hypothesized ordinality.

To investigate Piaget's theory of object concept development, a series of 6 tasks was administered in a combined longitudinal/cross-sectional design incorporating a number of methodological controls. The tasks spanned the entire sensorimotor period and included single versus sequential displacements combined with visible or invisible hidings. 36 infants from 5 to 32 months of age at initial testing were drawn equally from day-care and home settings. All infants received the 6 tasks during each of 3 testing sessions over a 6-month period. Clear evidence was obtained for task ordinality as proposed by Piaget, with ordinality coefficients ranging from .71 to .82 for the 3 testing sessions. Performance changes across the 3 sessions were also ordinal in 80% of the cases. Expected age, task, and session effects and accompanying interactions were also obtained.

Age Factors↗
PubMed1975

The effect of stimulus complexity on infant visual attention and habituation.

Infant visual attention and habituation were examined with a procedure providing independent assessment of an infant's latency of orienting to a pattern (attention getting) and his subsequent fixation of that pattern (attention holding). 18 male and 18 female, 17-week-old infants were given 2 trials with a red circle, 16 trials with either a 2 times 2, 8 times 8, or 24 times 24 checkerboard pattern, then 2 more red-circle trials. The major results were that habituation occurred in fixation time with males habituating more than females, and that a general decrease occurred in latency with females selectively increasing or decreasing their latency depending upon the pattern they had previously seen. These results indicated the necessity of separating attention-getting from attention-holding measures and that both sexes remembered something about the visual patterns but demonstrated that memory differently.

Attention↗
PubMed1974

The temperature dependence of the movement of sodium ions associated with nerve impulses.

1. The movement of sodium ions across the membrane of the squid giant axon was measured by the use of radioactive tracers. Unidirectional fluxes were measured at rest and when the nerve was stimulated. The difference was considered the extra flux association with nerve impulses.2. The extra influx in intact axons at room temperature was 5.5 p-mole/cm(2). impulse. At 6 degrees C the extra influx was 6.5 p-mole/cm(2). impulse giving a Q(10) of 1/1.2.3. In perfused axons a Q(10) of 1/1.6 was obtained for the extra sodium influx in bracketed experiments on individual axons.4. The Q(10) of the extra sodium efflux associated with nerve impulses was found to be 1/1.2 in intact axons.5. Hodgkin & Huxley had predicted a much larger temperature dependence for the extra fluxes. If this difference between prediction and experiment does not result from some experimental error, then the class of models for the ion fluxes suggested by Hodgkin & Huxley may be inapplicable.

Animals↗