Construction of direction selectivity in V1: from simple to complex cells

Despite detailed knowledge about the anatomy and physiology of the primary visual cortex (V1), the immense number of feed-forward and recurrent connections onto a given V1 neuron make it difficult to understand how the physiological details relate to a given neuron’s functional properties. Here, we focus on a well-known functional property of many V1 complex cells: phase-invariant direction selectivity (DS). While the energy model explains its construction at the conceptual level, it remains unclear how the mathematical operations described in this model are implemented by cortical circuits. To understand how DS of complex cells is constructed in cortex, we apply a nonlinear modeling framework to extracellular data from macaque V1. We use a modification of spike-triggered covariance (STC) analysis to identify multiple biologically plausible "spatiotemporal features" that either excite or suppress a cell. We demonstrate that these features represent the true inputs to the neuron more accurately, and the resulting nonlinear model compactly describes how these inputs are combined to result in the functional properties of the cell. In a population of 59 neurons, we find that both simple and complex V1 cells are selective to combinations of excitatory and suppressive motion features. Because the strength of DS and simple/complex classification is well predicted by our models, we can use simulations with inputs matching thalamic and simple cells to assess how individual model components contribute to these measures. Our results unify experimental observations regarding the construction of DS from thalamic feed-forward inputs to V1: based on the differences between excitatory and inhibitory inputs, they suggest a connectivity diagram for simple and complex cells that sheds light on the mechanism underlying the DS of cortical cells. More generally, they illustrate how stage-wise nonlinear combination of multiple features gives rise to the processing of more abstract visual information

Alien Registration- Goulette, Blanche A. (Dexter, Penobscot County)

https://digitalmaine.com/alien_docs/11270/thumbnail.jp

Wilson March

https://digitalcommons.library.umaine.edu/mmb-ps/2493/thumbnail.jp

Alien Registration- Haines, Blanche A. (Medway, Penobscot County)

https://digitalmaine.com/alien_docs/8250/thumbnail.jp

Tuberculosis and Poverty: Why Are the Poor at Greater Risk in India?

Background: Although poverty is widely recognized as an important risk factor for tuberculosis (TB) disease, the specific proximal risk factors that mediate this association are less clear. The objective of our study was to investigate the mechanisms by which poverty increases the risk of TB. Methods: Using individual level data from 198,754 people from the 2006 Demographic Health Survey (DHS) for India, we assessed self-reported TB status, TB determinants and household socioeconomic status. We used these data to calculate the population attributable fractions (PAF) for each key TB risk factor based on the prevalence of determinants and estimates of the effect of these risk factors derived from published sources. We conducted a mediation analysis using principal components analysis (PCA) and regression to demonstrate how the association between poverty and TB prevalence is mediated. Results: The prevalence of self-reported TB in the 2006 DHS for India was 545 per 100,000 and ranged from 201 in the highest quintile to 1100 in the lowest quintile. Among those in the poorest population, the PAFs for low body mass index (BMI) and indoor air pollution were 34.2% and 28.5% respectively. The PCA analysis also showed that low BMI had the strongest mediating effect on the association between poverty and prevalent TB (12%, p = 0.019). Conclusion: TB control strategies should be targeted to the poorest populations that are most at risk, and should address the most important determinants of disease—specifically low BMI and indoor air pollution

Developing Elementary Science Concepts by an Individualized Approach

In developing a concept of the universe at the elementary level many learning aids are utilized. Visual presentations, direct observations, experimentations and critical reading accompanied by discussions serve to enhance a child\u27s understanding of a concept. Moreover, it is apparent that all elementary school children do not arrive at the same level of understanding of scientific phenomena. There are many children who do not respond effectively to experimentation and critical reading and thus must rely on direct observations and visual presentation in arriving at a lower level of conceptual development. Other children who are more sophisticated may understand the orderliness of scientific phenomena and display knowledge of the vastness and complexities of our universe. Branley (1), Sheckles (13), and Vinacke (14) have pointed out that differentiation and gradual progression take place in concept development as one matures. Further credence is given to this belief by Russell (12) who states that concept development seems to move along a continuum from simple to complex, from concrete to abstract, from undifferentiated to differentiated, from discrete to organized, from egocentric to more social

Blanche A. Sawyer Correspondence

Entries include brief biographical information and a handwritten biographical letter of reply to the Maine State Library from a New York lawyer on receipt of a letter forwarded by her former classmate who had corresponded with the Maine state librarian on Sawyer\u27s behalf