181-184 of 184 Results

Article

Visual Shape and Object Perception  

Anitha Pasupathy, Yasmine El-Shamayleh, and Dina V. Popovkina

Humans and other primates rely on vision. Our visual system endows us with the ability to perceive, recognize, and manipulate objects, to avoid obstacles and dangers, to choose foods appropriate for consumption, to read text, and to interpret facial expressions in social interactions. To support these visual functions, the primate brain captures a high-resolution image of the world in the retina and, through a series of intricate operations in the cerebral cortex, transforms this representation into a percept that reflects the physical characteristics of objects and surfaces in the environment. To construct a reliable and informative percept, the visual system discounts the influence of extraneous factors such as illumination, occlusions, and viewing conditions. This perceptual “invariance” can be thought of as the brain’s solution to an inverse inference problem in which the physical factors that gave rise to the retinal image are estimated. While the processes of perception and recognition seem fast and effortless, it is a challenging computational problem that involves a substantial proportion of the primate brain.

Article

What Is a Neuronal Ensemble?  

Luis Carrillo-Reid and Rafael Yuste

Despite over a century of neuroscience research, the nature of the neural code, that is, how neuronal activity underlies motor, sensory, and cognitive functions, remains elusive. Understanding the causal relation between neuronal activity and behavior requires a new conceptual paradigm that considers groups of neurons, instead of individual neurons, as the functional building blocks of the brain. These “neuronal ensembles,” defined as groups of neurons with coordinated activity that are reliably recalled by sensory stimuli, motor programs, or cognitive states, could be basic modular functional units of neural circuits. This hypothesis is consistent with past and present neuroscience results and could provide a broader framework to more effectively decipher the neural code in normal brains and provide new insights into how abnormal brain activity could lead to mental and neurological disease.

Article

What is a Sequence? The Neural Mechanisms of Perceptual, Motor, and Task Sequences Across Species and Their Interaction with Addiction  

Theresa M. Desrochers and Theresa H. McKim

Sequences permeate daily life. They can be defined as a discrete series of items or states that occur in a specific order with a beginning and end. The brain supports the perception and execution of sequences. Perceptual sequences involve tracking regularities in incoming stimuli, such as the series of sounds that make up a word in language. Executed sequences range from the series of muscle activations used by a frog to catch a fly to a chess master mapping her next moves. How the brain controls sequences must therefore scale to multiple levels of control. Investigating how the brain functions to accomplish this task spans from the study of individual cells in the brain to human cognition. Understanding the neural systems that underlie sequential control is necessary to approach the mechanistic underpinnings of complex conditions such as addiction, which may be rooted in difficult-to-extinguish sequential behaviors. Current research focuses on studies in both animal and human models and spans the levels of complexity of sequential control and the brain systems that support it.

Article

Xenacoelomorpha Nervous Systems  

Pedro Martínez, Volker Hartenstein, and Simon G. Sprecher

The emergence and diversification of bilateral animals are among the most important transitions in the history of life on our planet. A proper understanding of the evolutionary process will derive from answering such key questions as, how did complex body plans arise in evolutionary time, and how are complex body plans “encoded” in the genome? the first step is focusing on the earliest stages in bilaterian evolution, probing the most elusive organization of the genomes and microscopic anatomy in basally branching taxa, which are currently assembled in a clade named Xenacoelomorpha. This enigmatic phylum is composed of three major taxa: acoel flatworms, nemertodermatids, and xenoturbellids. Interestingly, the constituent species of this clade have an enormously varied set of morphologies; not just the obvious external features but also their tissues present a high degree of constructional variation. This interesting diversity of morphologies (a clear example being the nervous system, with animals showing different degrees of compaction) provides a unique system in which to address outstanding questions regarding the parallel evolution of genomes and the many morphological characters encoded by them. A systematic exploration of the anatomy of members of these three taxa, employing immunohistochemistry, in situ hybridization, and high-throughput transmission electron microscopy, will provide the reference framework necessary to understand the changing roles of genes and gene networks during the evolution of xenacoelomorph morphologies and, in particular, of their nervous systems.