Neuromechanistic Model of Auditory Bistability

Sequences of higher frequency A and lower frequency B tones repeating in an ABA- triplet pattern are widely used to study auditory streaming. One may experience either an integrated percept, a single ABA-ABA- stream, or a segregated percept, separate but simultaneous streams A-A-A-A- and -B---B--. During minutes-long presentations, subjects may report irregular alternations between these interpretations. We combine neuromechanistic modeling and psychoacoustic experiments to study these persistent alternations and to characterize the effects of manipulating stimulus parameters. Unlike many phenomenological models with abstract, percept-specific competition and fixed inputs, our network model comprises neuronal units with sensory feature dependent inputs that mimic the pulsatile-like A1 responses to tones in the ABA- triplets. It embodies a neuronal computation for percept competition thought to occur beyond primary auditory cortex (A1). Mutual inhibition, adaptation and noise are implemented. We include slow NDMA recurrent excitation for local temporal memory that enables linkage across sound gaps from one triplet to the next. Percepts in our model are identified in the firing patterns of the neuronal units. We predict with the model that manipulations of the frequency difference between tones A and B should affect the dominance durations of the stronger percept, the one dominant a larger fraction of time, more than those of the weaker percept—a property that has been previously established and generalized across several visual bistable paradigms. We confirm the qualitative prediction with our psychoacoustic experiments and use the behavioral data to further constrain and improve the model, achieving quantitative agreement between experimental and modeling results. Our work and model provide a platform that can be extended to consider other stimulus conditions, including the effects of context and volition.     

Monozygotic and dizygotic twins' retrospective and current bereavement-related behaviors: an evolutionary perspective.

The present study compared bereavement responses of 325 monozygotic (MZ) and 176 dizygotic (DZ) adolescent and adult twins following the loss of their co-twins. A subset of twins completed the Grief Experience Inventory using a retrospective time frame, while a second subset completed it using a current time frame. It was hypothesized that MZ twins (in both retrospective and current groups) would report higher levels of grief-related behavior than DZ twins, consistent with Hamilton's (1964) concept of inclusive fitness. Discriminant function and profile analyses yielded supportive findings, but only for the retrospective MZ and DZ twin comparisons. Females in both groups expressed higher levels of bereavement-related behavior than males. Findings are discussed with reference to theoretical aspects of grief and mourning.     

Regulation of functionally related enzymes during alternative developmental programs

Cell aggregates of Dictyostelium discoideum can either construct fruiting bodies directly at the site of aggregation or transform into migrating slugs and move away. The latter can be induced at any time by appropriate environmental signals to stop migrating and construct fruits. In this and a previous publication (P. C. Newelland M. Sussman, J. Mol. Biol., 49 (1970)627), the patterns of accumulation and disapperance of three enzymes have been examined during these alternative developmental programs. The enzymes are: UDP-glucose pyrophosphorylase (EC 2.7.7.9), UDP-galactose 4-epimerase (EC 5.1.3.2), and UDP-galactose : polysaccharide galactosyl-transferase. The results indicate that:

1.

1. The performances of all three enzymes differ drastically but consistently in these two developmental modes in respect to times at which the activities begin to accumulate, the periods of accumulation, and the periods of disappearance. There is no evidence that the three are coordinately controlled with respect to any of the above.     

Accumulation of uridine diphosphoglucose pyrophosphorylase in Dictyostelium discoideum via preferential synthesis

At the end of the exponential growth phase, the enzyme UDP-glueose pyrophosphorylase is present in the vegetative cells of Dictyostelium discoideum NC4 (haploid) at a low level (about 0.05% of total protein). During the initial stages of fruiting body construction, while the cells are entering into multicellular aggregates, the enzyme level remains constant, but increases dramatically thereafter reaching a peak (about 0.5% of total protein) at the end of fruiting body construction, and then partially decreasing. Previous studies have shown that both the accumulation and disappearance are keyed to the flow of morphogenetic events.In this study, cells were labeled with amino acids for different periods throughout the sequence. The enzyme was quantitatively immune-precipitated from crude cell extracts, the precipitate was washed and redissolved, and the enzyme protein separated by acrylamide gel electrophoresis in order to estimate the differential incorporation ratio, i.e. $\text{disints}\text{min in enzyme protein per 10}{}^8\text{cells}\text{disints}\text{min in total protein per 10}{}^8\text{cells}\text{× 100}$ for each labeling period. During the initial stages, when the enzyme level remained relatively constant, this ratio was about 0.03 to 0.04%. As the enzyme began to accumulate it rose progressively, attaining levels of 0.6 to 0.8% toward the end of fruiting body construction before declining. The data are not consistent with the theory of Gustafson and Wright (1973) that differential turnover controls the level of this enzyme during the development of D. discoideum. They are consistent with the conclusion that directed changes in the differential rate of synthesis of UDP-glucose pyrophosphorylase is the controlling element.The estimates of enzyme content are based on a value for the specific enzyme activity of 100,000 units/mg enzyme, which had been determined previously using samples of the enzyme purified to apparent physical homogeneity. This figure has been confirmed in the present study by quantitative immuneprecipitation of the enzyme from crude extracts of homogeneously labeled cells. The method can be generally used to determine if a specific biological activity estimate obtained with a purified protein is consistent with its activity when measured before or during purification.